Applied Science, Faculty of
Engineering, School of (Okanagan)
DSpace
UBCO
Lindsay, Tobias
Master of Applied Science - MASc
University of British Columbia
With the increasing interest of electric vehicles as a form of clean transportation, automotive manufacturers are pushing to release attractive electric vehicle models for consumers. The main limitation for electric vehicle development, is developing a battery with high energy density as well as a high power density without sacrificing the cycle life of the battery. One of the proposed solutions is using a hybrid energy storage system, which combines an energy storage device with a high power density, such as a supercapacitor, along with one with a high energy density, such as a lithium ion battery. This combination creates a more ideal energy storage system for use in electric vehicles, improving the batteries cycle life without sacrificing performance or range. This document discusses the supercapacitor hybrid energy storage system and the challenges involved in implementing a practical system, focusing on the DC-DC converter required to connect the supercapacitor to the battery. A novel startup technique and application of the flying capacitor multi-level, multi-phase bi-directional DC-DC converter will be presented and the simulation results of a practical prototype discussed. This includes the design, component selection, startup sequence and programing of the converter.
A Multilevel-Multiphase DC-DC Converter for use inBattery-Supercapacitor Hybrid Energy Storage SystemsbyTobias LindsayElectronics Engineering Technology Diploma, Okanagan College , 2013B.A.Sc, The University of British Columbia , 2016A THESIS SUBMITTED IN PARTIAL FULFILLMENTOF THE REQUIREMENTS FOR THE DEGREE OFMASTER OF APPLIED SCIENCEinTHE COLLEGE OF GRADUATE STUDIES(Electrical Engineering)THE UNIVERSITY OF BRITISH COLUMBIA(Okanagan)July 2019c© Tobias Lindsay, 2019The following individuals certify that they have read, and recommend to the Faculty ofGraduate and Postdoctoral Studies for acceptance, a thesis/dissertation entitled:A Multilevel-Multiphase DC-DC Converter for use in Battery-Supercapacitor Hybrid En-ergy Storage SystemsSubmitted by Tobias Lindsay in partial fulfillment of the requirements for thedegree of Master of Applied Science .Dr. Wilson Eberle, Faculty of Applied Science, UBC OkanaganSupervisor, ProfessorDr. Liwei Wang, Faculty of Applied Science, UBC OkanaganSupervisory Committee Member, ProfessorDr. Martin Ordonez, Faculty of Electrical and Computer Engineering, UBC VancouverSupervisory Committee Member, ProfessorDr. Alexander Uhl, Faculty of Applied Science, UBC OkanaganAdditional ExamineriiAbstractWith the increasing interest of electric vehicles as a form of clean transportation, automo-tive manufacturers are pushing to release attractive electric vehicle models for consumers.The main limitation for electric vehicle development, is developing a battery with high en-ergy density as well as a high power density without sacrificing the cycle life of the battery.One of the proposed solutions is using a hybrid energy storage system, which combines anenergy storage device with a high power density, such as a supercapacitor, along with onewith a high energy density, such as a lithium ion battery. This combination creates a moreideal energy storage system for use in electric vehicles, improving the batteries cycle lifewithout sacrificing performance or range.This document discusses the supercapacitor hybrid energy storage system and the chal-lenges involved in implementing a practical system, focusing on the DC-DC converterrequired to connect the supercapacitor to the battery. A novel startup technique and appli-cation of the flying capacitor multi-level, multi-phase bi-directional DC-DC converter willbe presented and the simulation results of a practical prototype discussed. This includesthe design, component selection, startup sequence and programing of the converter.iiiLay SummaryElectric vehicles typically rely on batteries to provide the energy storage needed to providepower to move the vehicle. Electric vehicle manufacturers are considering using multipleenergy storage types to optimize power output, range and battery cycle life. Howeverthe main challenge in this strategy is connecting the two sources in an efficient and lowweight manner. This thesis proposes a novel startup sequence to make multi-level DC-DCconverters capable of bi-directional operation possible. This results in a converter with veryhigh efficiency in a lightweight package, making it ideal for use in electric vehicles.ivPrefaceThis dissertation is original, unpublished, independent work by the author, Tobias Lindsay.vTable of ContentsAbstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iiiLay Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ivPreface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vTable of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viList of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xList of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiiList of Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xivList of Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviAcknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xviii1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.1 Electric Vehicle Batteries . . . . . . . . . . . . . . . . . . . . . . . 21.1.2 Hybrid Energy Storage Systems . . . . . . . . . . . . . . . . . . . 51.2 Power Electronics for Hybrid Energy Storage Systems . . . . . . . . . . . 8vi1.3 Thesis Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.2 Half-Bridge Synchronous Buck DC-DC Converter . . . . . . . . . . . . . . 102.3 Half-Bridge DC-DC Converter Topology Variations . . . . . . . . . . . . . 112.3.1 Soft Switched Converters . . . . . . . . . . . . . . . . . . . . . . . 112.3.2 Specialty Inductor Converters . . . . . . . . . . . . . . . . . . . . 122.4 Increased Power Density Strategies . . . . . . . . . . . . . . . . . . . . . . 142.4.1 Multiphase Converters . . . . . . . . . . . . . . . . . . . . . . . . 142.4.2 Multilevel Converters . . . . . . . . . . . . . . . . . . . . . . . . . 152.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 Design of the Bi-Directional Four-Level Two-Phase Flying Capacitor DC-DC Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.2 Flying Capacitor Comverter Theory . . . . . . . . . . . . . . . . . . . . . 193.3 Four Level Two Phase Flying Capacitor Circuit Operation and ComponentSelection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.3.1 Four-Level Converter and 2-Phase Operation . . . . . . . . . . . . 223.4 Four Level Two Phase Flying Capacitor Component Selection . . . . . . . 253.4.1 Switch Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 253.4.2 Inductor Selection and Design . . . . . . . . . . . . . . . . . . . . 283.4.3 Flying Capacitor Selection . . . . . . . . . . . . . . . . . . . . . . 323.4.4 Filter Capacitor Selection . . . . . . . . . . . . . . . . . . . . . . . 333.5 Ancillary Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363.5.1 Control Card . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37vii3.5.2 Start Up Relays . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373.5.3 Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383.5.4 Boot-strap and Gate Drivers . . . . . . . . . . . . . . . . . . . . . 383.5.5 Summary of Selected Components . . . . . . . . . . . . . . . . . . 403.6 Startup Sequence for Flying Capacitor Converters . . . . . . . . . . . . . . 424 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454.2 Bi-Directional Half-Bridge Simulation Circuit . . . . . . . . . . . . . . . . 454.3 Four Level Two Phase Simulation Circuit . . . . . . . . . . . . . . . . . . 484.4 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494.4.1 Operational Functionality . . . . . . . . . . . . . . . . . . . . . . . 494.4.2 Bi-Directional Operation . . . . . . . . . . . . . . . . . . . . . . . 504.4.3 Current Control Strategy . . . . . . . . . . . . . . . . . . . . . . . 514.4.4 Four Level Startup Results . . . . . . . . . . . . . . . . . . . . . . 534.4.5 Efficiency Across Duty Cycle and Load Range . . . . . . . . . . . 554.5 Discussion Comparing Converter Designs . . . . . . . . . . . . . . . . . . 574.5.1 Converter Power Densities . . . . . . . . . . . . . . . . . . . . . . 574.5.2 Converter Component Area Comparisons . . . . . . . . . . . . . . 594.5.3 Converter Cost Comparisons . . . . . . . . . . . . . . . . . . . . . 604.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615 Conclusions and Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . 625.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625.2 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625.3 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 635.3.1 Prototype Testing and Re-Design . . . . . . . . . . . . . . . . . . . 63viii5.3.2 Efficiency Optimization . . . . . . . . . . . . . . . . . . . . . . . . 64Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65A 4-Level 2 Phase DC-DC Converter Schematic . . . . . . . . . . . . . . . . . . 69B Bill of Materials for the 4-Level 2-Phase DC-DC Converter and Half BridgeConverter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71B.1 4-Level 2-Phase DC-DC converter Bill of Materials . . . . . . . . . . . . . 72B.2 Half Bridge Bill of Materials . . . . . . . . . . . . . . . . . . . . . . . . . 73C Four Level Two Phase Converter Start-up Sequence C Code . . . . . . . . . 74D Printed Circuit Board Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 79D.1 Top Layer of the PCB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80D.2 Second Layer of the PCB . . . . . . . . . . . . . . . . . . . . . . . . . . . 81D.3 Third Layer of the PCB . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82D.4 Bottom Layer of the PCB . . . . . . . . . . . . . . . . . . . . . . . . . . . 83ixList of TablesTable 1.1 Comparisons of currents and losses within a battery . . . . . . . . . . . 5Table 2.1 States of operation for a 4-Level converter . . . . . . . . . . . . . . . . 17Table 3.1 Required phase shifts for Four-Level Two-Phase (4L2P) converter oper-ation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Table 3.2 Bi-directional DC-DC converter required parameters . . . . . . . . . . . 25Table 3.3 Inductor design parameters . . . . . . . . . . . . . . . . . . . . . . . . 29Table 3.4 Inductor core properties . . . . . . . . . . . . . . . . . . . . . . . . . . 31Table 3.5 Inductor design summary for the 4L2P design . . . . . . . . . . . . . . 32Table 3.6 Flying capacitor summary for the 4L2P design . . . . . . . . . . . . . . 33Table 3.7 Input capacitor summary for the 4L2P design . . . . . . . . . . . . . . . 36Table 3.8 Control card input and output requirements. . . . . . . . . . . . . . . . . 37Table 3.9 Selected components summary . . . . . . . . . . . . . . . . . . . . . . 41Table 3.10 Required pre-charge voltages for 4-Level 2-Phase flying capacitor con-verter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43Table 4.1 Half-bridge simulation parameters . . . . . . . . . . . . . . . . . . . . . 46Table 4.2 4L2P simulation parameters . . . . . . . . . . . . . . . . . . . . . . . . 49Table 4.3 Proportional Integral (PI) controller response results and comparisons . . 52xTable 4.4 Required pre-charge voltages . . . . . . . . . . . . . . . . . . . . . . . 55Table 4.5 Efficiency comparisons between Half-Bridge (HB) and 4L2P converters . 56Table 4.6 Loss comparisons between HB and 4L2P converters . . . . . . . . . . . 57Table 4.7 Inductor Size and cost comparisons between HB and 4L2P converters . . 58Table 4.8 Size and cost comparisons between capacitors . . . . . . . . . . . . . . 58Table 4.9 Size comparisons between heat sinks . . . . . . . . . . . . . . . . . . . 59Table 4.10 Component Printed Circuit Board (PCB) area comparisons . . . . . . . . 60Table 4.11 Component prototype cost comparisons between the 4L2P converter andthe HB converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61xiList of FiguresFigure 1.1 Basic equivalent circuit for an Electric Vehicle (EV) battery . . . . . . . 3Figure 1.2 UDDS drive cycle example . . . . . . . . . . . . . . . . . . . . . . . . 4Figure 1.3 HESS topologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Figure 2.1 Bi-directional Synchronous Buck . . . . . . . . . . . . . . . . . . . . . 11Figure 2.2 2 Phase DC-DC converter . . . . . . . . . . . . . . . . . . . . . . . . 13Figure 2.3 Variable Inductor DC-DC converter . . . . . . . . . . . . . . . . . . . 14Figure 2.4 2-Phase bidirectional converter . . . . . . . . . . . . . . . . . . . . . . 15Figure 2.5 Split Capacitor 3-Level . . . . . . . . . . . . . . . . . . . . . . . . . . 16Figure 2.6 Flying Capacitor 4-Level converter . . . . . . . . . . . . . . . . . . . . 17Figure 3.1 Relative ripple currents for N-Level converters up to 5-Levels . . . . . . 20Figure 3.2 Generalized 4L2P Flying Capacitor (FC) converter . . . . . . . . . . . 23Figure 3.4 FOM comparisons of GaN, SiC and Si Switches . . . . . . . . . . . . . 27Figure 3.5 Minimum inductance for the 4-Level converter prototype . . . . . . . . 30Figure 3.6 Minimum input capacitance . . . . . . . . . . . . . . . . . . . . . . . 35Figure 3.7 Complete 4-Level 2-Phase bi-directional DC-DC converter circuit show-ing bootstrap and startup components . . . . . . . . . . . . . . . . . . 39Figure 4.1 Half Bridge PSIM Circuit used for simulation results . . . . . . . . . . 47xiiFigure 4.2 Key Waveforms for half-bridge converter . . . . . . . . . . . . . . . . 47Figure 4.3 4L2P PSIM circuit used for simulation results . . . . . . . . . . . . . . 48Figure 4.4 Key waveforms for the four-level two-phase converter . . . . . . . . . . 50Figure 4.5 Sweep from -60A to 60A showing bi-directional operation . . . . . . . 51Figure 4.6 Half bridge and 4L2P step response . . . . . . . . . . . . . . . . . . . 52Figure 4.7 Complete 4L2P bi-directional DC-DC converter circuit showing all thecapacitors that require pre-charging . . . . . . . . . . . . . . . . . . . 54Figure 4.8 Half bridge and 4L2P converter efficiency comparisons . . . . . . . . . 56xiiiList of Acronyms4L2P Four-Level Two-PhaseBDC Bi-Directional DC-DC ConverterBOM Bill of MaterialsCO2 Carbon DioxideDSP Digital Signal ProcessorESL Equivalent Series InductanceESR Equivalent Series ResistanceESS Energy Storage SystemEV Electric VehicleFOM Figure of MerritFC Flying CapacitorGAN Galium NitrideHB Half-BridgeHESS Hybrid Energy Storage SystemxivHV High VoltageICE Internal Combustion EngineLI-ION Lithium-IonLV Low VoltageMOSFET Metal Oxide Semiconductor Field Effect TransistorMPP Molypermalloy PowderPCB Printed Circuit BoardPI Proportional IntegralPSIM PowerSim (software)PWM Pulse Width ModulationRMS Root Mean SquareSI SiliconSIC silicon CarbideSC SupercapacitorsUDDS Urban Dynamometer Driving ScheduleZCS Zero Current SwitchingZVS Zero Voltage SwitchingxvList of SymbolsCFC Flying Capacitor CapacitanceCin Required Input Capacitor CapacitanceCLVmin Low Voltage Side Required CapacitanceD Duty CycleDe f f Effective Duty CyclefindRipple Inductor Ripple FrequencyfL Inductor Frequencyfsw Switching FrequencyIDC DC Current∆iL Inductor Ripple CurrentILavg Average Inductor Current∆iLmax Peak Inductor CurrentILpk−pk Peak to Peak Inductor Ripple CurrentImin Minimum CurrentIrms RMS currentLHal f Bridge Half Bridge InductanceL4Level 4-Level InductanceMaxFCripple Max Voltage Ripple on the Flying CapacitorsxviN Number of Converter Levelsηconv Converter efficiencyNphases Number of Converter PhasesPloss Converter Power LossRint Internal ResistanceRv Cooling Constant∆T Allowable Temperature DifferenceVbat Battery VoltageVcap Capacitor VoltageVC1 Voltage of Input Capacitor C1Vds Drain-Source VoltageVheatsink Volume of Heat SinkVHV High Voltage Side Voltage∆Vinpp Peak to Peak Input Voltage RippleVLmax Maximum Inductor Voltage∆VLV Low Voltage Side VoltageVmin Minimum VoltageVSC Supercapacitor VoltagexviiAcknowledgmentsI would like to thank my fiance´ Megan Ruesgen and my family for their support duringmy studies. Also I would like to thank Ford Motor Co. for providing the funding for thisproject. I would also like to thank my supervisor Dr. Wilson Eberle for his support andexpertise throughout the project.xviiiChapter 1Introduction1.1 MotivationWith the stricter Carbon Dioxide (CO2) emission standards being implemented by govern-ments around the world, auto manufacturers are considering alternatives over the traditionalInternal Combustion Engine (ICE) [1]. Currently the best alternative is the Electric Vehi-cle (EV), as they have zero tailpipe emissions, are up to three times more efficient thanstandard ICE vehicles and can be powered by renewable energy sources. EVs also havesimpler mechanical systems, increasing reliability and reducing maintenance cost. Thereare however still many challenges in EV development, the main one being electrical energystorage. Current EVs rely on Lithium-Ion (LI-ION) batteries for energy storage, while thesebatteries are capable of giving EVs 150km+ all electric range with sufficient power for goodperformance, they are expensive, costing about a third of the total vehicle cost, and due tobattery degradation, require replacement after about 10-15 years [2]. This degradation andreplacement cost, effectively eliminates the financial benefits from owning an EV (fuel &maintenance savings), making them less attractive to consumers [3]. This makes the de-velopment of economical and efficient electrical energy storage a priority for automotive1manufacturers.1.1.1 Electric Vehicle BatteriesWhen automotive manufactures design EVs, they must balance three key parameters whenselecting a battery chemistry. The first is the power density, which is the power that abattery can deliver per unit mass and partially determines the performance of an EV. Thesecond is the energy density, which is how much energy a battery can store per unit mass.The last is the cycle life of the battery, which is how many complete charge-dischargecycles the battery can go through before it’s capacity is reduced to 80% of its originalcapacity. Looking at the various battery chemistries available, most will have desirablecharacteristics in two of these categories while sacrificing the third [4]. Since range, cyclelife and performance are important to consumers, manufactures will typically use a highenergy density battery and then oversize it to achieve the desired performance and cyclelife. This increases the cost, size and weight of the electric vehicle, limiting their adoption.1.1.1.1 Current Electric Vehicle BatteriesAs of 2019 the best commercially available battery for use in electric vehicles is the LI-IONbattery, as they have the best energy density (100-250 Wh/kg), good power density (up to2 kW/kg) and a good cycle life (1000+ full charge/discharge cycles) [5]. Recently batterymanufacturing cost have reduced significantly and are predicted to continue dropping incost due to increased demand and the implementation of mass production for EV batteries[6]. Despite this reduction in cost the battery remains the most expensive component inEVs and are prone to degradation.1.1.1.2 Battery Degradation FactorsResearch has identified several degradation factors that cause batteries to lose capacityover time [2], [3]. One of the main factors that has been identified is that high temperatures2accelerate the degradation of batteries [2]. Looking at the basic equivalent circuit for abattery as seen in Figure 1.1, they have a Equivalent Series Resistance (ESR) at the output.This shows that as electrical current demand increases, batteries are prone to heating. Thepower loss in the battery can be approximated using Equation 1.1, where Irms is the RootMean Square (RMS) current in amperes and Rint is the internal resistance of the batterypack.BATRintLoadFigure 1.1: Basic equivalent circuit for an EV batteryP= I2rmsRint (1.1)1.1.1.3 Effects of Driving Dynamics on Battery DegradationThere are many factors which determine how much power is required of the motor, invert-er/controller and the vehicles Energy Storage System (ESS) in an EV. These are calledpower dynamics and are effected by the vehicles acceleration/deceleration rates, travelspeed, vehicle aerodynamics and the gradient/slope of the road. An example of this isgiven in Figure 1.2, which shows a simulated current based on a Ford Focus EV, drivingthe first 150 seconds of the Urban Dynamometer Driving Schedule (UDDS) drive cycle.During acceleration events the vehicles power demand peaks, causing large spikes in cur-rent demand. During deceleration events, EVs can recover some of the kinetic energy ofthe vehicle, sending power back into the batteries, hence the negative current and during3cruising the power requirements are relatively small and more constant. So due to thesedriving dynamics the current drawn is also highly dynamic. This dynamic current causesIRMS to be significantly greater than the average DC current (IDC). An example of this isdemonstrated in Table 1.1 which is based off the example in Figure 1.2, it shows that theRMS current is about 1.6 times higher than the average DC current, causing an 2.54 timesgreater internal power loss. These additional losses cause the battery temperature to in-crease more than if just IDC were drawn from the battery. This increased temperature cancause significant thermal stress on the battery reducing its cycle life, potentially requiringearly replacement. This however, presents an opportunity to reduce the electrical currentdynamics on the battery, by combining a LI-ION battery with a second energy storage de-vice with a very low ESR, such as a Supercapacitors (SC). This combination makes a moreideal ESS, which is good for delivering highly dynamic currents, while drawing a currentmuch closer to IDC, reducing internal battery losses. This combination is called a HybridEnergy Storage System (HESS).50 100 150-20Accel. Accel. Accel. Accel. Const.Const. Decel.Decel. Decel. Aux.Aux.020406080Speed (km/h) Iload (A)Figure 1.2: Simulated currents for the first 150 seconds of the UDDS drive cycle for aFord Focus EV, where acceleration events are highlighted in blue,deceleration in yellow, constant speed in green and auxiliary loading in red4Table 1.1: Comparisons of currents and losses within a battery assuming a Rint = 0.3ΩParameter Current Approx LossesIDC 12.81A 49.22WIRMS 20.42A 125.09WIncrease 1.59x 2.54x1.1.2 Hybrid Energy Storage SystemsA HESS is comprised of a combination of energy storage technologies. Typically the goalof a HESS is to combine one energy storage technology with a good energy density, withanother which has a good power density. Maximizing range and improving battery cyclelife, without sacrificing performance. Typical combinations include fuel cell-battery, fuelcell-supercapacitors and battery-supercapacitor combinations. Since this thesis is focusedon the applications of a HESS in a battery electric vehicle, this section will focus on thebattery-supercapacitor combination.1.1.2.1 SupercapacitorsUnlike electrochemical batteries, supercapacitors store electricity directly in an electricfield. They use the high surface area of activated carbon to store the charge, giving them ahigh energy storage capability, compared with traditional capacitors and a very high powerdensity, when compared to batteries. Typical energy densities of 5-10 Wh/kg [7] can beachieved compared to traditional capacitors 0.15-1.2 Wh/kg [8] and power densities up to11 kW/kg, which is less than capacitors 270kW/kg-1000kW/kg but much greater than bat-teries 100W/kg-900W/kg [8]. They also have a very low ESR, and are capable of rechargingat the same rate as they discharge. This combination of high power density, relatively highenergy density, equal charge-discharge rates and low ESR makes supercapacitors ideal for5low frequency (0.1-5 Hz) high-power RMS current reduction for dynamic loads. So bycombining supercapacitors with LI-ION batteries you can form a HESS which has the en-ergy storage of a battery and the power density of a SC.1.1.2.2 Hybrid Energy Storage Systems Setup OptionsThere are various ways to setup a battery-supercapacitor HESS. The four main HESS se-tups that are most common among researchers [9–11] are shown in Figure 1.3. The firststrategy is shown in Figure 1.3a, places a series SC pack with a voltage rating equal to themaximum battery voltage in parallel with the battery. This has the advantage of simplicityand efficiency since it does not require a Bi-Directional DC-DC Converter (BDC), howeverdue to the low voltage variation on the DC bus, only about 5-10% of the SC stored energyis used minimizing its effectiveness [8].The second method is a fully decoupled HESS, shown in Figure 1.3b. This strategyplaces a BDC between the SC pack and the main voltage bus and another between thebattery pack and the main voltage bus. This means that the power flow of both devicescan be fully controlled. This strategy provides the most flexibility in the control strategy,allowing the effective use of 75% of the energy storage of the SC and full control of bothenergy sources. If an ideal BDC existed this method would be the best option, however it isnot an effective solution considering the increased cost, converter losses and weight [12].The third type is a partially decoupled battery HESS, which is shown in Figure 1.3c.This configuration has the advantage that the SC works as a low pass filter simplifyingcontrol and allows increased SC energy usage [12]. However, the voltage swing of the SCcan reduce the efficiency of the DC-AC motor drive and the DC-DC converter for this setuprequires a very high-power rating, with high cost, losses and mass, limiting the benefits.The last setup shown in Figure 1.3d is the partially decoupled SC HESS which uses aBDC to connect the SC to the battery bus, this has the advantages of 75% SC energy usage,6smaller power rating for the BDC and simple control. Most researchers agree that this is thebest setup for a HESS systems as it results in the lowest cost, highest efficiency, smallestoverall package and simplest to control HESS [9, 10, 13].SC BAT 3 PhaseMotorDCDCDCACSCBAT 3 PhaseMotorDCDCDCACSC BAT 3 PhaseMotorDCDCSCBAT 3 PhaseMotorDCACDCDCDCACa)b)c)d)Figure 1.3: a) Passive HESS b) Fully decoupled HESS c) Partially decoupled battery HESSd) Partially decoupled SC HESSDue to the low power requirement for the BDC and the simplest control the partiallydecoupled HESS is considered the most feasible and practical. This method however stillrequires a BDC with high efficiency and high power density.71.2 Power Electronics for Hybrid Energy StorageSystemsFor partially decoupled HESS configuration, the LI-ION battery cannot be directly con-nected to the SC as the SC voltage must vary significantly as it discharges to maximize thestored energy. Also the magnitude and direction of current flow must be fully controllableas to maximize the effectiveness of the HESS. To accomplish this power electronics must beused. There are a variety of bi-directional topologies can be used, which can transfer powerbetween the sources in either direction despite the voltage difference. A bi-directional con-verter can boost the SC voltage to the battery voltage during SC discharge and buck thebattery voltage to the SC voltage during SC recharge.A good selection of a BDC topology and its corresponding components is crucial for asuccessful HESS system as it must transfer all the power that the SC provides twice, oncefor recharge and again for discharge. Therefore, the ideal DC-DC converter for a HESS willhave bi-directional current flow, have 95%+ efficiency over a wide duty cycle range, be lowcost and have a high-power density minimizing mass.One of the main components which determines the characteristics of a BDC is the induc-tor. The inductor effects various aspects of the converter including, the transient response,the quality of the regulated voltage/current, the power density and the efficiency. As suchit is an important component to optimize where a smaller inductor results in better tran-sient response and power density, while larger inductors usually results in better efficiencyand power quality. The main component that affects inductor size is the ripple/switchingfrequency of the converter.81.3 Thesis OrganizationThe thesis is organized into 5 chapters. Chapter 1, presents the need for HESS, the impor-tance of a BDC and an overview of power electronics for HESS applications. Chapter 2,presents an overview and comparison of the different strategies used by other researchersto maximize power density and efficiency of BDCs. Chapter 3 presents the design processfor the Four-Level Two-Phase (4L2P) converter, the control strategy used and the novelaspects of the design. Chapter 4 presents the design and simulation results, verifying theeffectiveness of the 4-Level 2-Phase approach as well as the control and startup sequenceperformance. Finally Chapter 5 presents the conclusions, summarizes the thesis results andpresents opportunities for future work.9Chapter 2Literature Review2.1 OverviewThis chapter is split into four sections, the first section, Section 2.2 discusses the typicalhalf-bridge synchronous buck converter, Section 2.3 discusses the variations of the tradi-tional BDC. Section 2.4, goes into the strategies to increase power density and efficiencyof the BDC, including multi-phase and multi-level topologies. Section 3.2 will discuss themulti-level converter in further detail.2.2 Half-Bridge Synchronous Buck DC-DC ConverterThe ability to have controlled bi-directional current flow is a necessity for a successfulHESS. Traditionally bidirectional current flow is achieved by using buck topologies usingtwo switches operated in synchronously.The synchronous buck converter is the most commonly used BDC in hybrid energy stor-age systems [14–21]. This is mainly due to their low component count and simple control.The topology configuration for a typical Half-Bridge (HB) synchronous buck converter ina SC based HESS is shown in Figure 2.1 along with the key waveforms, showing basic10operation, .C2C1SCBat S1S2 L1b)a)0AS1 Gate SignalsS2 Gate SignalsL1 Inductor CurrentFigure 2.1: a) Bi-directional Synchronous Buck Converter for HESS b) Gating andinductor waveformsThe main advantages of the synchronous buck converter are simple setup, good effi-ciency, simple control and a low component count [14–21]. The main disadvantage, how-ever, is that due to the high voltage and current stresses, the capacitors, inductors and MetalOxide Semiconductor Field Effect Transistor (MOSFET)s end up being large and expensive.2.3 Half-Bridge DC-DC Converter Topology VariationsThe HB BDC topology discussed in the previous section is effective and simple to imple-ment, however this comes at the cost of lower power densities and efficiencies. Thesedisadvantages have been the main focus of researchers for improvement. The solutionspresented in this section use the same HB topology but with some variations to attempt toimprove power density and efficiency. These potential variations will be discussed in thefollowing section, highlighting the advantages and disadvantages of each.2.3.1 Soft Switched ConvertersSoft switched converters are widely used in power electronics to achieve a zero-powertransition for the switches by modifying the current or voltage waveform so that a Zero11Voltage Switching (ZVS) or a Zero Current Switching (ZCS) events can occur. This methodcan virtually eliminate switching losses allowing a converter to use lower cost switches orto operate at higher switching frequencies while maintaining a good efficiency [22, 23].While this is desirable, the current/voltage shaping circuits and control can be complicatedand costly. Soft switched converters are rarely proposed for use in HESS prototypes sinceit becomes increasingly more difficult to modify the current or voltage waveforms in highpowered converters. Also since silicon Carbide (SIC) and Galium Nitride (GAN) deviceshave become economical, reliable and very efficient, similar benefits can be achieved withless complexity and similar cost [22].2.3.2 Specialty Inductor ConvertersHigh power, high current DC-DC converters often require very large inductor cores toprevent saturation during high current demand and to minimize ripple current. This resultsin a very expensive, high volume, heavy inductor, which is undesirable in an EV. Thereare a few potential solutions that have been proposed, that modify the inductor. The first iscoupling inductors and the other is a variable inductor.2.3.2.1 Coupled InductorCoupled inductors are used in multi-phase type converters which place two or more HBconverters in parallel and run their Pulse Width Modulation (PWM) signals out of phase.Coupled inductors use multiple inductor coils wrapped around a common core. By doingthis a mutual inductance is formed resulting in a higher inductance and saturation currentper unit volume than if the two inductors were wrapped on separate cores. A two phase ex-ample of this is shown in Figure 2.2. This type of converter has been used for bi-directionalconverters to help improve power density and reduce cost [20, 24].12C2C1SCBat S1S2S3S4L1L2b)a) S1 & S2 Gate SignalsS3 & S4 Gate SignalsL1 & L2 & Combined Inductor CurrentsFigure 2.2: 2-Phase bi-directional DC-DC converter using coupled inductors b) Gatingand inductor waveforms2.3.2.2 Variable InductorAnother proposed solution to the problem of large inductor requirements is the variableinductor [17]. A variable inductor, is formed by adding a secondary winding on the inductorwrapped in the opposite direction of the primary. This secondary winding is connectedto an auxiliary circuit which provides a bias current proportional to the DC current inthe primary, canceling out the flux generated from the primary. This reduces the coresaturation, allowing a smaller core to be used which only has to manage the AC flux [17].The basic setup for a single-phase system with a variable inductor is shown in Figure 2.3along with the key waveforms demonstrating its operation. While this setup significantlyreduces the core size it adds significant circuit complexity and requires additional power torun the axillary circuit increasing losses.13C2C1SCBat S1S2L1ab)a)0AS1 Gate SignalsS2 Gate SignalsL1a & L1b Inductor CurrentL1bCurrentControlledConverterFigure 2.3: a) Variable inductor based half-bridge bi-directional DC-DC topology [17] b)Gating and inductor waveforms2.4 Increased Power Density StrategiesThe power density of a power converter is important when used in EVs as additional weightcan reduce range and efficiency of the vehicle. This section will discuss some of the powerconverter topologies which can significantly improve the power density of bi-directionalpower converters.2.4.1 Multiphase ConvertersA multiphase converter is derived from the synchronous buck converter, where multipleconverters are placed in parallel and their gate signals are driven out of phase. This shiftsthe inductor waveforms so that when combined they have a canceling effect and multipli-cation of ripple frequency. The 2-phase converter is the simplest example of a multiphaseconverter, and is shown in Figure 2.4 along with its key waveforms demonstrating its basicoperation.The main benefit to this topology is that each phase shares the current equally allowingthe use of switches and inductors with reduced current ratings, potentially saving cost and14the ability to operate at higher power levels.C2C1SCBat S1S2S3S4 L1L2b)a) S1 & S2 Gate SignalsS3 & S4 Gate SignalsL1 & L2 & Combined Inductor CurrentsFigure 2.4: a) A 2-phase multi-phase converter b) Gating and inductor waveformsThe multiphase converter has many advantages including inductor ripple current can-cellation and frequency multiplication minimizing input and output capacitor size, the op-portunity to couple inductors minimizing inductor size, potential redundant phases andcurrent sharing reducing current stresses on components reducing size and cost. The maindisadvantages are the higher component count and the need for high voltage switches. Mul-tiphase converters have also been popular among researcher in for use in HESS systems[13, 14, 25].2.4.2 Multilevel ConvertersMultilevel converters have the potential to significantly increase power densities of powerconverters [26]. With new advanced semiconductors (GAN and SIC), multilevel convertersare beginning to gain popularity for medium to high power applications.2.4.2.1 Split Capacitor Multilevel ConverterThe split capacitor multilevel converter, splits the HV bus voltage using a capacitor divider,giving multiple voltage levels, this can reduces the inductor size by up to 1/(N− 1)2 andreduces switch voltage stress by 1/(N-1) where N is the number of voltage levels. While15split capacitor converters can have more than 3 levels, the 3-level split capacitor topologyshown in Figure 2.5a is the most common [27–29]. The basic operation is demonstrated inFigure 2.5b showing the key waveforms.C3C1SCBATS1S2S3S4L1C2b)0AS1 & S2 Gate SignalsS3 & S4 Gate SignalsL1 Inductor Currenta)Figure 2.5: a) Split Capacitor 3-Level DC-DC converter b) Gating and inductorwaveformsThe split-level converter has the advantages of reduced voltage stresses on the switches,reduced inductor and output capacitor size. The disadvantages include complex control,need to balance the voltage splitting capacitors, and increased component count.2.4.2.2 Flying Capacitor ConvertersThe Flying Capacitor (FC) topology is a popular multilevel converter for researchers [26–28], [30–36]. While this topology is very similar to the split capacitor converter, it has thebenefit of natural balancing on the capacitors, this means that the capacitors will remainat their desired voltage without requiring additional control loops, making it significantlyeasier to have N-level converters higher than three. This allows significant improvementsin power density with simpler control. The Figure of Merrit (FOM) improvements of lowvoltage GAN and high voltage SIC technologies have allowed FC converters to functionat a very high efficiency despite having multiple switches in the conduction path. This16C4C1SCBATC2 C3 L11/3Vi2/3ViS2S4S6S5S3S1b)0AS1 & S6 Gate SignalsL1 Inductor CurrentS3 & S6 Gate SignalsS2 & S5 Gate Signals+ VL -Va+-iC2 iC3VoVi++--+ +- -Figure 2.6: a) Flying Capacitor 4-Level converter b) Gating and inductor waveformsallows very high efficiency, high power density and fast transient response converter to bebuilt for a reasonable cost. A 4-Level example of a FC converter is shown in Figure 2.6.The operation of the 4-Level converter is given in Table 2.1, showing the various switchcombinations and current paths.Table 2.1: States of operation for a 4-Level converterState S1 S2 S3 S4 S5 S6 iC2 iC3 Va VL1 0 0 0 1 1 1 0 0 0 −Vo2 0 0 1 0 1 1 0 - (1/3)Vi (1/3)Vi−Vo3 0 1 0 1 0 1 - + (1/3)Vi (1/3)Vi−Vo4 0 1 1 0 0 1 - 0 (2/3)Vi (2/3)Vi−Vo5 1 0 0 1 1 0 + 0 (1/3)Vi (1/3)Vi−Vo6 1 0 1 0 1 0 + - (2/3)Vi (2/3)Vi−Vo7 1 1 0 1 0 0 0 + (2/3)Vi (2/3)Vi−Vo8 1 1 1 0 0 0 0 0 Vi Vi−Vo17The main advantages to the flying capacitor multilevel converter is that it has high con-version ratios, reduced inductor size/copper losses, reduced low voltage filter capacitance,equal Low Voltage (LV) stress on the switches (allowing the use of low FOM switches) andself-balancing FCs [35]. The main disadvantages are the increased component count andcostly FCs.2.5 SummaryThis chapter reviewed the approach of other researchers to the use of DC-DC converters forelectric vehicle hybrid energy storage systems. It discussed the various topologies proposedin literature, highlighting their advantages and disadvantages. The literature on DC-DCconverters, does not come to a definitive conclusion, however after evaluating the variousadvantages and disadvantages discussed for each topology, the flying capacitor multilevelconverter closely matches the requirements for a HESS converter. This is due to its high-power density, relatively low cost and its high efficiency. This review lead to a decisionto implement a two phase four level flying capacitor multilevel converter, in the partiallydecoupled SC HESS configuration. This combination results in the maximum power density,minimal cost and very high efficiency. The use of a multilevel system also allows the use ofGAN switches which have the best FOM available, allowing high switching frequency andreduced conduction losses. The addition of the HESS with an optimized DCDC converter,will help extend the battery cycle life, improving EV value. This will make them moredesirable consumers and help reduce the environmental impacts of personal transportation.18Chapter 3Design of the Bi-Directional Four-LevelTwo-Phase Flying Capacitor DC-DCConverter3.1 OverviewThis chapter gives a detailed overview into the design of the proposed 4L2P FC converter.It will cover the practical theory of operation, design and selection of the main powercomponents including GaN power switches, power inductors, input and output capacitorsand the flying capacitors. It will also propose the part numbers which match the designedvalues and present a practical prototype design. Additionally a novel startup method isproposed, which allows the FC topology to be used as a bi-directional converter.3.2 Flying Capacitor Comverter TheoryThe theoretical operation of a flying capacitor DC-DC converter is similar to the traditionalhalf bridge converter. The relationship between duty cycle and output voltage is the same19and is given by Equation 3.1.D=VcapVbatηconv(3.1)Multilevel converters are capable of significantly reducing the size of passive compo-nents in a DC-DC converter. This potential for size reduction is demonstrated in Figure 3.1,which shows the relative inductor ripple currents of two to five level multi-level converters.Selection of the number of levels can minimize inductor size even further depending on theduty cycle range.00.10.20.30.40.50.60.70.80.910 0.2 0.4 0.6 0.8 1ΔiL/ΔiLmax2L Duty Cycle 2-Level3-Level4-Level5-LevelFigure 3.1: Relative ripple currents for N-Level converters up to 5-LevelsThe flying capacitor converter uses N − 2 flying capacitors, where N is the number20of levels, to split the input voltage into multiple levels, each flying capacitors voltage isreduced by Equation 3.2 at each stage towards the load. This gives the converter N voltagelevel options.VFCred =VHVN−1 (3.2)The switches use phase shifted pulse width modulated signals to take advantage of themultiple voltage levels to minimize inductor ripple and minimize switch voltage stress.Each switch pair are synchronously switched, and each set of switch pairs are phase shiftedby 360o/(N− 1). This PWM strategy allows the flying capacitors to naturally balance, aseven number FC converters have a improved immunity to capacitor imbalance [36]. Thissimplifies control as there is no need for a capacitor balancing control loop. It also reducesthe switch voltage stress to Equation 3.3.Vds =VHVN−1 (3.3)One of the main advantages to the multi-level converters is the inductor size reduction.This reduction is possible due to the frequency multiplication and the voltage stress reduc-tion. The inductor frequency is given by Equation 3.4. The voltage across the inductor isgiven by Equation 3.5. When these two factors are combined the inductor size reductioncan be approximated by Equation 3.6. This however, will vary depending on duty cyclerange of operation and the inductor design.fL = fsw(N−1) (3.4)VLmax =VHVN−1 (3.5)21L4LevelLHal f Bridge=1(N−1)2 (3.6)3.3 Four Level Two Phase Flying Capacitor CircuitOperation and Component SelectionThe flying capacitor converter can also benefit from having multiple phases in parallel.So the proposed converter for HESS applications is a four level FC converter run in a twophase configuration or 4L2P for short. This section will discuss the operation and designof a practical 4L2P converter.3.3.1 Four-Level Converter and 2-Phase OperationThe proposed 4L2P converter is shown in Figure 3.2, it consists of two 4-Level convertersplaced in parallel, with shared input and output capacitors. Phase A is the master phase andPhase B is the slave phase. The source is modeled as a EV battery and the load is modeledas a SC, allowing for bi-directional operation.22C6C1 SCBATS1S6C2S2S5C3S3S4L1S7S12C4S8S11C5S9S10L2Phase APhase BFigure 3.2: Generalized 4L2P FC converter power circuit highlighting phase A and phaseBTo maximize the benefits of using a multi-phase multi-level combination, it is neces-sary to phase shift the PWM signals precisely. Table 3.1, summarizes the required phasesfor each switch pair. These phase shifts allow the frequency multiplication and correct volt-age combinations to occur in the 4-Level converter and the extra 180o phase shift on thesecond phase allows inductor current cancellation to occur, minimizing the output ripplecurrent, that the LV capacitors must filter. This ripple current cancellation is demonstratedin Figure 3.3, showing that the combined ripple current peak is half of the inductor ripplecurrent in the 4-Level converter.23Table 3.1: Required phase shifts for 4L2P converter operationComplementary Switch Pair Required Phase ShiftS1 & S6 0oS2 & S5 120oS3 & S4 240oS7 & S12 180oS8 & S11 300oS9 & S10 420o02468100 0.2 0.4 0.6 0.8 1Current Ripple (A) Duty Cycle Inductor CurrentOutput Current RippleFigure 3.3: 4L2P inductor current ripple and combined current ripple.243.4 Four Level Two Phase Flying Capacitor ComponentSelectionThe main components of the 4L2P FC converter include twelve switches, two inductors,four flying capacitors, an input capacitor and an output capacitor. To build a high perfor-mance 4L2P FC converter, good component selection is essential. The required parametersfor a prototype HESS systems BDC are found in Table 3.2.Table 3.2: Bi-directional DC-DC converter required parametersParameter Required ValuePeak Power Rating 15kWMinimum Efficiency 95%+Battery Voltage 360VSC Voltage Swing 125-250VDuty Cycle Range 0.35-0.7Inductor Ripple Current 10AInductor DC Current ±30AMaximum Output Current ±60AMax FC voltage ripple 10%Max High Voltage (HV) voltage ripple 3.6VMax LV voltage ripple 1.25V3.4.1 Switch SelectionProper selection of the switches in a multilevel converter is essential to having a successful4L2P converter with high efficiency. The switches must have proper voltage rating, low turnon and turn off losses as well as a very low conduction loss as the current is passing through253 switches at all times in a 4-level converter. The main benefit during switch selection fora 4-Level topology is that the converter can use switches with lower voltage ratings, theseswitches often have significantly better FOMs than HV switches. This also allows the useof GAN devices, which are typically only available in lower voltage levels.3.4.1.1 Voltage RatingThe minimum voltage rating for a switch in a N-Level converter is given by Equation 3.7.Substituting the converter parameters the min voltage is 132V. Looking at the switchesavailable a 200V switch is the minimum voltage with a good safety factor of about 35%.Vmin =VHV (1+MaxFCripple)(N−1) (3.7)3.4.1.2 Current RatingThe current rating of the switches is determined by the peak inductor current which com-bines the average inductor current plus half the inductor ripple current. This is given byEquation 3.8, and using the converter parameters gives a minimum switch current rating of35A.Imin = ILavg+ILpk−pk2(3.8)3.4.1.3 Wide Band-Gap Switching TechnologiesIn recent years, there have been major advancements in switching technologies with theintroduction of wide band-gap switching devices. The two major new technologies aresilicon carbide (SIC) and gallium nitride (GAN) devices. SIC devices are typically used forhigh voltage applications and GAN devices are typically used in lower voltage applications.Figure 3.4 compares the FOM with respect to blocking voltage ratings of Silicon (SI), SIC26and GAN switching technologies. The FOM is the product of the gate charge (Qg), which isan indicator of the switching losses, and on state resistance (Rdson) which is an indicator ofthe conduction losses of a switch. Therefore a lower FOM indicates lower average losses.The FOM of about 10 devices per technology are presented. Looking at the data it canbe seen that GAN devices have significantly lower FOM for voltages up to 650V and SICdevices are best for applications above 900V. The best SI devices only come close to SICaround 650V, but are significantly higher at all other voltages. This plot does not take intoaccount cost or other factors, but does give an idea of which technology will achieve thebest efficiencies given a certain voltage range in hard switching applications.101001000100001000000 200 400 600 800 1000 1200 1400Figure of Merrit (Qg(nC)*Rdson(mΩ)) Drain-Source Voltage Rating (V) SiSiCGaNFigure 3.4: FOM comparisons for current SI MOSFET, SIC MOSFETs and GAN switchingdevices as of September 2018), note that the FOM axis is in a logarithmic scale27Based on the required voltage and current ratings for the 4L2P converter and the avail-able switches from Figure 3.4, the switch that has the best FOM and sufficient voltage andcurrent stress ratings is Efficient Power Conversions 200V 48A GAN switch with the partnumber EPC2034. This switch is also one of the most affordable GAN switch at ten dollarseach.3.4.2 Inductor Selection and DesignInductor selection and design is essential to maximize the efficiency and performance in aDC-DC converter. This selection becomes a challenge, in high current and high frequencyapplications, often requiring a custom inductor design to be used. This section will discussthe sizing and design of high efficiency, low weight inductors for use in the 4L2P prototype.3.4.2.1 Inductor SizingSince the converter is a multiphase multi-level converter the ripple current can be higherthan in a traditional half bridge converter. So the designed ∆iL was selected to be 10Aor about 30%, the slightly higher than normal ripple current is possible due to the 2-Phase topology, which allows ripple cancellation, along with low loss MolypermalloyPowder (MPP) core materials. The design requirements for the inductor are summarizedin Table 3.3.28Table 3.3: Inductor design parametersParameter Required ValueTopology 4-Level 2-PhaseFull load current per phase 30ACurrent Ripple 10APeak Current 35AConverter Switching Frequency 100 kHzSince the converter is required to operate over a wide duty cycle range it is helpful toplot the minimum inductance with respect to duty cycle to ensure proper design. The equa-tion to calculate the required inductance given a certain duty cycle is given in Equation 3.9.The graph generated from this equation is shown in Figure 3.5. Looking at the operat-ing duty cycle range for the converter it is found that the minimum required inductance is10µH.L=VHV (CEILING((N−1)D,1)N−1 −D)(MOD(D, 1N−1)fsw∆iL) (3.9)290246810120 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Min Inductance (uH) Duty Cycle Operating AreaFigure 3.5: Minimum inductance for the 4-Level converter prototype with respect to dutycycle for a ∆iLmax = 10A3.4.2.2 Inductor DesignThe inductor ripple frequency in a multilevel converter is multiplied as shown in Equa-tion 3.10. This indicates that for a 4-Level converter, the inductor current ripple frequencyis three times the converters switching frequency. This makes the inductor ripple frequency300kHz for a 4L2P converter.findRipple = (N−1) fsw (3.10)Looking at the commercially available inductors in the 10µH+ range, most are to large,expensive, high loss or don’t have sufficient saturation current ratings. Therefore a customdesigned inductor is necessary. The most important aspect for inductor design is the core30selection. Table 3.4 summarizes the most common core material properties. The MPP corehas the lowest AC losses and good permeability, saturation and temperature characteristicsmaking it ideal for a high frequency high ripple converter.Table 3.4: Inductor core properties for MPP, High Flux, Kool Mu Iron Powder and Ferritecore typesCore Material MPP High Flux Kool Mu Iron Powder FerriteRelative Permeability 12-300 14-160 12-125 10-100 900-3000Saturation (Bsat) 0.7T 1.5T 1T 1.2-1.4T 0.3-0.5TMax Temp (Celcius) 200 200 200 Varies 200-300AC core loss Lowest Moderate Low Highest ModerateCore Shape(s) Toroid Toroid Varies Varies VariesDC bias Better Best Good Good GoodAlloy Composition Fe Ni Mo Fe Ni Fe Si Al Fe Fe Mn ZnThe inductor design for the 4L2P converter followed the recommended design processfor MPP cores provided on the manufactures website [37]. The final design is summarizedin Table 3.531Table 3.5: Inductor design summary for the 4L2P design using a MPP coreParameter ValueCore Part Number C055083Wire Gauge 18 AWGWire Type Litz WireNumber of Parallel Strands 3Number of turns 14AC core losses @ full load 4.5 WDC losses @ full load 2.83 WTotal losses @ full load 7.33 WCore Mass 86gCore Cost (USD) $10No Load Inductance 18µHFull Load Inductance 12µH3.4.3 Flying Capacitor SelectionThe flying capacitor selection is also important to the proper operation of the converterpreventing excessive voltage stress on the switches. A 10% ripple voltage gives a goodbalance between switch voltage stress and capacitor size/cost. The equation for determin-ing the required capacitance for a given ripple voltage is given in Equation 3.11. Whenthe converter parameters are entered into Equation 3.11, the minimum required value is4.67µF for the 250V FC and 9.72µF for the 120V FC.CFC =imax(N−1)Vripple fsw (3.11)32The selection of the capacitor material is important for successful operation of the FCconverter. Since the FCs must handle very high currents the best option is to use multipleceramic capacitors in parallel, as ceramic capacitors have the lowest ESR and EquivalentSeries Inductance (ESL). It is also necessary to add some low value ceramic decouplingcapacitors to minimize the overshoot cause by the switches by providing a high frequencylow impedance path between the high side and low side switches.While ceramic capacitors have good performance, they are prone to voltage bias capac-itance reduction and often will lose 50% of their rated capacitance at 50% of their ratedvoltage. This must be noted when selecting the capacitors and either a capacitor with a sig-nificantly higher capacitance or voltage rating must be chosen to ensure that the requiredcapacitance is met when the capacitor is fully biased.Table 3.6 summarizes the selected capacitors for the 4L2P converter including the de-coupling capacitors.Table 3.6: Flying capacitor summary for the 4L2P designComponent Part Number Parallel Total Biased Capacitance240V FC CKG57NX7T2W225M500JH 6 6µF240V FC decoupling CGA6M4X7R2J683K200AA 3 0.12µF120V FC C5750X7T2E225K250KA 8 8.8µF120V FC decoupling CGA6M4X7R2J683K200AA 3 0.14µF3.4.4 Filter Capacitor SelectionThe HV and the LV filter capacitors are important to filter the voltage ripple cause by theswitching action of the converter. The allowed ripple is 1% of the voltage at the HV, andLV side.333.4.4.1 High Voltage Filter Capacitor SelectionThe selection of the high voltage filter capacitor is very important to the performance andfunctionality of the 4L2P converter. This is because the HV side capacitor must filter asquare current wave at the converters switching frequency. Additionally the input capac-itors must provide a low impedance path between the high side and low side switches tominimize voltage overshoot. Since the filter is for a multilevel converter the input capaci-tance must be calculated using the effective duty cycle given by Equation 3.12, then placedin the input capacitance equation Equation 3.13. Since the converter operates over a largeduty cycle range, it is helpful to plot the required capacitance over the full range of opera-tion as seen in Figure 3.6, from this graph the minimum Cin is 10.42µF .De f f = (N−1)Mod(D, 1N−1) (3.12)Cin=De f f (1−De f f )ILavg∆Vinpp fswNphases(3.13)340246810120 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Minimum Cin (uF)Duty CycleOperating AreaFigure 3.6: Minimum input capacitance for the 4-Level converter prototype with respectto duty cycleSelecting the right capacitors for the input capacitor is also important as it must supplycurrent during slow current transients as well as filter the main switching frequency. Thisis usually accomplished by using bulk capacitors such as film or electrolytic capacitorsalong with low ESR and ESL capacitors such as ceramic capacitors. It can also be useful toadd some small value ceramic capacitors to aid in minimizing switch overshoot. Table 3.7summarizes the capacitors selected for the input.35Table 3.7: Input capacitor summary for the 4L2P designComponent Part Number Parallel Total Biased CapacitanceBulk Input Caps B32774P6475K000 2 9.4µFCeramic Input Caps CKG57NX7T2J105M500JH 4 2µFDecoupling Input Caps C5750X7T2E225K250KA 4 0.1µF3.4.4.2 Low Voltage Filter Capacitor SelectionThe low voltage filter capacitor is mainly used to smooth out the inductor ripple current toensure a stable output voltage/current. Since the ripple frequency is multiplied significantlyand the two inductor ripples partially cancel out the output capacitors are significantly re-duced and can be comprised solely of ceramic capacitors. This aids in efficiency and powerdensity of the design. Equation 3.14 can be used to determine the minimum capacitancerequired to achieve a selected ripple voltage. This results in a minimum capacitance of1.67µF . Three CKG57NX7T2W225M500JH 2.2µF ceramic capacitors are placed in par-allel to achieve 2.3µF when fully biased satisfying the filtering requirements.CLVmin =∆iLmax8∆VLV fswNPhases(N−1) (3.14)3.5 Ancillary ComponentsTo make a functional prototype there are a variety of ancillary components that are neces-sary. These include a controller, startup relays, voltage and current sensors and bootstrapand gate drivers. This section will cover the selection of these components and provide abrief description of each.363.5.1 Control CardThe control card is necessary to implement any desired control loops and convert the con-trol signals into PWM signals with the proper phase shifts. For a 4L2P design there arespecific requirements for the control card. These input and output requirements of thecontrol card are summarized in Table 3.8. In addition to these requirements, it must becompatible with PowerSim (software) (PSIM) code generation feature and the Digital Sig-nal Processor (DSP) oscilloscope feature. The f28335 control card from Texas Instrumentssatisfies these requirements.Table 3.8: Control card input and output requirements.Requirement Description ValuePWM channels 6Digital Outputs 5Analog to Digital inputs 63.5.2 Start Up RelaysThe startup relays are necessary to implement the proposed startup sequence and they mustbe able to handle the required voltages and currents. The system consists of two main powerrelays and one high voltage startup relays. The high voltage startup relay must switch thefull 360V input voltage with a series resistor to limit pre-charge currents, to implement thisa KT12-1A-40L-SMD 500V reed relay was selected. The power relays must conduct thefull input and output currents, therefore their on state resistance must be low, however theyare only switched when the voltage and current through them are near zero. Therefore theswitch voltage and current ratings don’t need to be very high. To satisfy these requirementsADJH23112 latching relays were selected.373.5.3 SensorsThe proposed startup sequence requires the input and output voltages at both sides of therelays. The current controllers for each phase also needs accurate current readings of theinductor currents.3.5.3.1 Voltage SensorsThe voltage sensors are required to measure the input and output voltages for the battery,SC and the input and output capacitors. These sensors are required for the startup sequence,however they don’t need to be to precise, therefore a basic resistor dividers provide suffi-cient accuracy for the controller. The sensors must drop the voltages down to 3.3V or loweras this is the limit of the built in analog to digital converters of the control card. Basic 1%0805 chip resistor provide sufficient voltage isolation and accuracy for this application.3.5.3.2 Current SensorsThe current sensors are used as feedback for the current control loop and must be reason-ably accurate. The current sensors must also be bi-directional, be capable of sensing at least40A in both directions, output an analog signal with minimal noise. The ACS730KLCTR-40AB-T current sensor meets these requirements, however it outputs a 0-5V signal and thecontrol card can only accept 0-3.3V, therefore a simple voltage divider must be used tobring the voltage within range of the DSP inputs.3.5.4 Boot-strap and Gate DriversThe 4L2P converter requires six gate drivers per phase, five of which are floating gatedrivers. Also GaN devices require well regulated 5V gate drive voltage. To achieve theserequirements a cascaded bootstrap strategy is implemented [36]. The diodes are setupin series, charging a bootstrap capacitor at each stage, Figure 3.7 shows how the bootstrap38circuit interfaces with the rest of the circuit. This method produces floating voltage sources,however the voltages vary due to diode voltage drops and the reverse conduction voltagesof GaN devices. The gate driver selected is the UCC27611, which has an internal 5Vregulator which can accept between 4-18V input voltages.C6C1 SCBATS1S6C2 S2S5C3 S3S4L1Phase APhase BC7 C8 C9C10C11C12ConConD1 D2 D3D5 D4S7S12C4S8S11C5S9S10L2C13 C14 C15C16C17C18ConConD6 D7 D8D10 D9R1 K1K2K3Vbat VC1 VC6 VSCFigure 3.7: Complete 4-Level 2-Phase bi-directional DC-DC converter circuit showingbootstrap and startup components393.5.5 Summary of Selected ComponentsTable 3.9 summarizes the main components selected and discussed in this section for the4L2P converter. A detailed bill of materials is available in Appendix B including all sup-porting components and connectors.40Table 3.9: Selected components summaryComponent Description Value Part NumberGAN Switch 200V 200V 48A EPC2034Inductor Core N/A C55083240V FC 450V 2.2µF CKG57NX7T2W225M500JH120V FC 250V 2.2µF KRM55TR72E225MH01KHV bulk capacitor 630V 1µF B32774P6475K000HV ceramic capacitor 630V 1µF CKG57NX7T2J105M500JHLV capacitor 450V 2.2µF CKG57NX7T2W225M500JHControl Card 150Mhz TMDSCNCD28335Voltage Sensors 8kΩ/1MΩ ERA-6AEB8061V / RT0805BRE071MLCurrent Sensors ±40A ACS730KLCTR?-40AB-TPrinted Circuit Board (PCB) 4-Layer 2oz ALLPCBStartup Relay HV 500V 500mA KT12-1A-40L-SMDStartup Power Relays 450V 60A ADJH23112Digital Isolator N/A ISO7710FDRGate Driver N/A UCC27611Bootstrap Diode 200V ES1DZener Diode 5.6V CZRU52C5V6Capacitor 0.1µF CL10A104KA8NNNCapacitor 1µF CC0805KKX7R8BB1Capacitor 0.22µF EMK107B7224KA-TCapacitor 1µF CL10A105KA8NNN413.6 Startup Sequence for Flying Capacitor ConvertersWhile FC converters have many advantages, they come with some challenges. One of thesechallenges especially in a bi-directional implementation of the FC converter is pre-chargingthe filter capacitors, flying capacitors and bootstrap capacitors to the required voltages atstartup. The main reason for this is that the typical battery voltage is 360V and the SCvoltage will be typically 250V and initially when the FCs are not charged any attempt atswitching will result in either 360V across the switches or 250V accross the switches whichare only rated to 200V, causing failure. Therefore some form of isolation and controlledstartup sequence is necessary to startup a multilevel FC converter without damage.Figure 3.7 shows the full circuit including the startup relays and the capacitors thatrequire pre-charging. The capacitors that require pre-charging can be grouped into 3 cat-egories. First are filter capacitors (C1, C6), second are flying capacitors(C2, C3, C4, C5)and lastly the bootstrap capacitors (C7-C18). The pre-charge voltages that these capacitorsrequire is summarize in Table 3.10.42Table 3.10: Required pre-charge voltages for 4-Level 2-Phase flying capacitor converterCapacitor Relative Voltage Actual VoltageC1 Vbat ∼ 360VC2, C4 23 ∗Vbat ∼ 240VC3, C5 13 ∗Vbat ∼ 120VC6 VSC ∼ 125-250VC7, C13 V12V −Vf wDiode ∼ 12VC8, C14 V12V −2∗Vf wDiode ∼ 11VC9, C15 V12V −3∗Vf wDiode ∼ 10VC10, C16 V12V −4∗Vf wDiode ∼ 9VC11, C17 V12V −5∗Vf wDiode ∼ 8VC12, C18 V12V −6∗Vf wDiode ∼ 7VTo pre-charge the capacitors without damaging the switches it is necessary to isolatethe HV and the LV sources as both sources exceed the maximum ratings of the switches(200V) and there needs to be a controlled pre-charge current to prevent damage to batteries,capacitors and switches. To accomplish this isolation three relays were used, one lowcurrent, high voltage reed relay that switches the input voltage through a startup resistorand two high current relays which turn on once there is near zero voltage across them.The proposed startup process for the 4L2P converter is summarized in the followingfour main steps.1. Start PWM signals with a duty cycle D= VSCVbat this pre-charges the bootstrap capacitors.If the output voltage is zero or near zero, the duty cycle is set to 0.05, which is theminimum duty cycle.432. Continue switching at D = VSCVbat and turn on K1 to start pre-charging through R1which limits startup current and drops the excess voltage across it. Also initialize thecontroller to have a output to D= VSCVbat .3. Once VC1 ≈ Vbat , K2 and K3 turns on, also the controller is enabled with a currentreference of zero amps. This stage is on for the duration of the turn on time of therelays (100ms)4. Now that everything is pre-charged and K2 and K3 are on. K1 turns off and the PIcontroller is fed the variable current reference and normal operation can begin.The C code implementation of the startup sequence can be found in Appendix C.44Chapter 4Simulation Results4.1 OverviewThis chapter will summarize the simulation results of the proposed four-level two-phasebi-directional converter and compare them to a similar traditional half-bridge converterdesign. It will cover the simulation circuits used, the operational functionality, the startupresults, simulated efficiency comparisons, and converter cost comparisons.4.2 Bi-Directional Half-Bridge Simulation CircuitTo help understand the benefits of the proposed 4L2P topology the typical bi-directionalhalf bridge topology will be used as a reference topology. To help make the topologycomparison fair, both converters use GaN switching devices and a MPP inductor core. Bothconverters also use the same switching frequency and input and output current/voltageripple parameters. The half bridge circuit is based off the GaN systems GSP65RXXHB-EVB evaluation board, with higher power components to match the power level of the4L2P design. A bill of materials is available in Appendix B. This Bill of Materials (BOM)is only an approximation as a full design was not completed, however it is sufficient to make45reasonable comparisons. The selected GaN device for these comparison is GaN SystemsGS66516 device. The circuit used for simulations is shown in Figure 4.1.The simulation uses the GS66516 GAN device model to simulate losses and uses a C-block to estimate the inductor losses. The parameters used in the simulation are given inTable 4.1.Table 4.1: Half-bridge simulation parametersParameter ValueSwitching Frequency 100 kHzInput Voltage 360VOutput Voltage 125V-250VDuty Cycle Range 0.35-0.7Output Current Range -60 to 60AInput Capacitance 130µFOutput Capacitance 20µFInductance 45µHGaN switches GS6651646C11130u360VVAAASH1SH245uL4C1220uVA1803.1SC3Figure 4.1: Half Bridge PSIM Circuit used for simulation resultsFigure 4.2 shows the basic operational waveforms of the HB converter.4045505560657075I(L4)0100200300VSH1VSH20 7.81u 15.62u 23.4u 31.24uTime (s)240260280300320340360Vin1Vout1Figure 4.2: Key Waveforms for half-bridge converter474.3 Four Level Two Phase Simulation CircuitThe 4L2P circuit has a similar setup to the HB circuit. It uses a simulation model forthe EPC2034 GaN devices and a C-block to calculate the inductor losses. The simulationparameters for the 4L2P converter is given in Table 4.2. Figure 4.3 shows the simulationcircuit for the 4L2P converter. All simulations were performed using PSIM, which is apower electronics simulation tool.L110uC5C620uC73604uC8VASC23.1S1 S2 S3S6 S5 S4VA10uL2C9C10SW1 SW2 SW3SW6 SW5 SW4AFigure 4.3: 4L2P PSIM circuit used for simulation results48Table 4.2: 4L2P simulation parametersParameter ValueSwitching Frequency 100 kHzInductor Frequency 300 kHzInput Voltage 360VOutput Voltage 125V-250VDuty Cycle Range 0.35-0.7Output Current Range -60 to 60AInput Capacitance 20µFOutput Capacitance 4µFInductance 10µHGaN switches EPC20344.4 Simulation Results4.4.1 Operational FunctionalityThe HB and the 4L2P topologies operate in a similar way. Their duty cycles are both afunction of input and output voltage and both have bidirectional capabilities. Howeverthe 4L2P has a few key differences, the inductor frequency is multiplied by three and itrequires that the FCs be balanced at 240V and 120V. Figure 4.2 shows the operation of thehalf bridge at full load operating as expected.The operation of the 4L2P converter is shown in Figure 4.4. The inductor currents areone of the main differences as they have a 300kHz switching frequency and passes onlyhalf of the total current. This is one of the main benefit of the 4L2P converter which allows49the use of a significantly reduced inductor size. Another difference is the converter usesFCs to split the input voltage, which, naturally balance to 240V and 120V as expected. Theother important factor is that the PWM signals are phase shifted by 120 degrees betweenswitch pairs and 180 degrees between phases to ensure proper operation.30405060I(L1)I(L2)Ioo0255075100125VS1VS60255075100125VS2VS50255075100125VS3VS4238240242244246VC2VC4118120122124126VC3VC50 7.81u 15.62uTime (s)240280320360VinVoutFigure 4.4: Key waveforms for the four-level two-phase converter4.4.2 Bi-Directional OperationSince the HB and the 4L2P converters are being used to charge and discharge SCs, theymust have bi-directional current flow and remain stable at all possible currents between the-60 to 60 ampere range of operation. The simulation results of a sweep between -60 to 60amps is shown in Figure 4.5. This demonstrates that the both the half bridge and the 4L2P50converters are stable throughout the full range of currents in both HV to LV and LV to HVdirections.0-25-50-75255075Ioo0-25-50-75255075I(L4)0.001 0.002 0.003 0.004 0.005Time (s)250275300325350VinVoutFigure 4.5: Sweep from -60A to 60A showing bi-directional operation4.4.3 Current Control StrategyThe current controllers used to regulate and control current flow, use a Proportional Inte-gral (PI) controller tunned using PowerSims SmartCtrl software. Figure 4.6 shows eachconverters response for a -60A to 60A step. This shows one of the other benefits of the4L2P topology, due to its small inductance and the inductors increased inductor ripple fre-quency it responds very quickly to changes in required current with minimal overshoot andsimple control. For the half bridge the settling time and overshoot were significantly largerthan the 4L2P converter.510-25-50255075 IoFC (A)Iref (A)0-50-10050100150 ILHB (A)Iref (A)0 31.25u 62.5u 93.75u 125u 156.25u 187.5u 218.75uTime (s)a)b)Figure 4.6: Step Response for Vbat=360V Vcap=250V from -60A to 60A a) The 4-Level2-Phase converter step response b) Half Bridge converter step responseTable 4.3 summarizes the performance of each converter with the PI controller, showingthat on average the 4L2P converter is over four times faster with four times less overshoot.This is desirable in a HESS system as it ensures the converter can deliver any requestedcurrent from the HESS controller, maximizing its effectiveness.Table 4.3: PI controller response results and comparisonsConverter Topology Rise Time Settling Time OvershootHalf Bridge 28.5µs 183.8µs 50.6A4L2P 6.57µs 44.5µs 11.1ARelative Improvement 4.37x 4.13x 4.56x524.4.4 Four Level Startup ResultsThe simulated results of the proposed 4L2P startup process is shown in Figure 4.7. Thisshows that the proposed startup sequence successfully pre-charges all required capacitancesto their respective voltages in a controlled manner. It is especially important to note that allswitch voltages remain well below the 200V limit of the GAN devices.Table 4.4 shows the desired pre-charge levels as well as the achieved levels before thecontroller was enabled. The results are as expected and very close to the desired values,there is a parameter that is set in the code which determines when the relays are turned on.So if necessary it can be set to a smaller number getting the values even closer, however itwill take longer to complete the pre-charge sequence.530-10-2010203040I(L2)I(L3)0100200300400VCinVCout050100150200250300VCFCHV1VCFCHV20255075100125150VCFCLV1VCFCLV204812VCBS0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18Time (s)050100150VS1-VS12Figure 4.7: Complete 4L2P bi-directional DC-DC converter circuit showing all thecapacitors that require pre-charging54Table 4.4: Required pre-charge voltages for 4-Level 2-Phase flying capacitor converterCapacitor Desired Voltage Simulated VoltageC1 ∼ 360V 335VC2, C4 ∼ 240V 223VC3, C5 ∼ 120V 111VC6 ∼ 250V 232VC7, C13 ∼ 12V 12VC8, C14 ∼ 11V 11VC9, C15 ∼ 10V 10VC10, C16 ∼ 9V 9VC11, C17 ∼ 8V 8VC12, C18 ∼ 7V 7V4.4.5 Efficiency Across Duty Cycle and Load RangeThe efficiency of DC-DC converters is one of the most important converter parameters,especially in battery powered applications, such as EVs. Figure 4.8 shows the simulatedtotal losses of the GaN switches of both the 4L2P converter and the HB converters acrossthe duty cycle range and at various output currents from -60A to 60A. The total GaNswitch losses of the 4L2P converter are significantly less than the HB over the full rangeof operation. Table 4.5 summarizes the efficiency differences between the two topologies.The 4L2P converter has a significantly improved average efficiency of 1.12% higher thanthe HB converter. This improvement is due to two main factors, the first is the FOM of theHB switch is higher than the 4L2P swiches and the limited availability of higher voltageswitches meant the selected HB switch must be operated nearer to it’s current limit which55can increase losses. Another factor that increases losses in the half bridge configuration isthe inductor is much larger so the winding and core losses are significantly increased. Thisis shown with the loss summary in Table 4.6.9797.59898.59999.5100EfficiencyFC EfficiencyHB0-25-50-75255075ILHBILcFC0.005 0.01 0.015 0.02 0.025 0.03Time (s)100150200250300350VinVoutFigure 4.8: Efficiency comparisons between HB converter and the proposed FC converterover the full duty cycle range at various loads (60A, 30A, 15A, -15A, -30Aand -60A)Table 4.5: Efficiency comparisons between HB and 4L2P convertersConverter Topology Peak Efficiency Minimum Efficiency Average Efficiency4L2P 99.8% 99.0% 99.53%Half Bridge 99.0% 97.1% 98.41%Difference 0.8% 1.9% 1.12%56Table 4.6: Loss comparisons between HB and 4L2P convertersConverter Topology Average Switch Losses Average Inductor Losses4L2P 27.7W 6.7WHalf Bridge 77.4W 29.2WDifference 2.8x 4.4x4.5 Discussion Comparing Converter Designs4.5.1 Converter Power DensitiesSince the proposed converter is to be used in EV applications, it is important to minimize thesize and weight of the converter while maintaining a good power output and efficiency. Themain components that effect a converters power density are the filter inductors, capacitorand the cooling components.4.5.1.1 Inductor Size ReductionThe inductor size and cost reduction is one of the main benefits of using the 4L2P topol-ogy. Table 4.7 shows an approximate comparison between the inductor design discussedin Chapter 3 for the 4L2P converter and a similarly designed inductor using the same corematerial and wire for the HB converter. This reduction in size of the inductor significantlyimproves the power density of the converter.57Table 4.7: Size and cost comparisons between inductors for HB and 4L2P converterdesigns, the 4L2P inductor numbers include both inductors for the 2-phasedesignConverter Topology Mass (g) PCB Area (cm2) Approx. Cost (USD)4L2P 215 16.1 ∼ $29Half Bridge 777 30.36 ∼ $100Relative Improvement 3.61x 1.88x 3.45x4.5.1.2 Capacitor Size ReductionFilter capacitor can be a significant contributor to converter weight and PCB board area.Table 4.8 compares the inductor mass,PCB board area and the approximate costs of therequired capacitors for the 4L2P and the HB reference design.Table 4.8: Size and cost comparisons between capacitors for HB and 4L2P converterdesigns, the 4L2P.Converter Topology Mass (g) PCB Area (cm2) Approx. Cost (CAD)4L2P 71 20.6 ∼ $160Half Bridge 366 84.8 ∼ $100Relative Improvement 5.15x 4.11x 0.63x4.5.1.3 Cooling Size ReductionHeat sinks are often one of the largest components of a power converter. The approximatevolume of a heat sink can be estimated using Equation 4.1 based on the estimated losses inthe previous section. Table 4.9 compares the estimated volumes and approximated mass ofthe required heat sinks.58Table 4.9: Size comparisons between heat sinks for the HB and 4L2P converter designsConverter Topology Volume (cm3) Approx. Mass (g)4L2P 228 207Half Bridge 630 566Relative Improvement 2.76x 2.76xVheatsink =PlossRv∆T(4.1)4.5.2 Converter Component Area ComparisonsSince a full design of the HB converter was not completed the PCB board area can’t bedirectly compared. However since we have a BOM for the HB, it is possible to comparethe component areas, which should approximately be proportional to the PCB area, whichpartially relates to power density. Table 4.10 compares the component areas, showing thatthe main area savings for the 4L2P converter are from the capacitors and inductors. The”Other” category is significantly higher, due to the addition of the startup components,however the total is about half that of the HB converter.59Table 4.10: Component PCB area comparisons between the 4L2P converter and the HBconverterComponent Category 4L2P Component Area HB Component Area DifferenceSwitches 1.44 1.36 1.06Power Capacitors 19.95 84.78 0.24Inductors 16.1 30.36 0.53Gate Drivers/Components 0.97 4.264 0.23Controller 8.05 8.05 1Sensors 1 0.56 1.78Other 24.03 5.588 4.30Total 77.40 134.96 0.574.5.3 Converter Cost ComparisonsThe cost of the converter is also an important factor in making a power converter for usein EVs. Table 4.11 shows the prototype cost of each component category based off theBOMs in Appendix B. The capacitor cost of the 4L2P converter is increased due to the FCs,which are ceramic capacitors, also the gate driver cost is significantly higher as the 4L2Pconverter requires twelve of them. The ”Sensor” and ”Other” costs are also increased asthe startup method requires additional sensors and components. Overall however the 4L2Pconverters component costs about 10% more overall, but the inductor cost for the HB wasestimated, since they are custom ordered and may be significantly more than the estimatedcost in which case the cost could be similar if not cheaper for the 4L2P converter.60Table 4.11: Component prototype cost comparisons between the 4L2P converter and theHB converterComponent Category 4L2P Cost HB Cost Rel. DifferenceSwitches $119.16 $153.38 0.78Power Capacitors $156.73 $97.18 1.61Inductors $24.7 ∼ $100 0.25Gate Drivers and Components $82.19 $27.02 3.04Controller $100 $100 1Sensors $20.38 $11.20 1.82Other $55.54 $20.378 2.78Total $558.70 $509.16 1.104.6 SummaryThe simulation verify that the proposed 4L2P converter is capable of operating across allrequired voltages and currents required of a battery-supercapacitor HESS system. It alsoachieves a very high relatively stable efficiency across all currents and voltages. The powerdensity is also greatly improved. The cost is also marginally different between the HBand the 4L2P converters, making the 4L2P converter a feasible alternative with improvedefficiency and power density.61Chapter 5Conclusions and Future Work5.1 OverviewSection 5.2 will give a a brief overview and the conclusions of the thesis. Section 5.3 willpresent some suggestions for future work to keep the project going.5.2 SummaryChapter 1 presented the importance and challenges of electric vehicle development. Italso presented the various challenges involved in developing an effective energy storagesystem, and introduced the idea of a hybrid energy storage system. It concluded discussingthe necessity of a bi-directional DC-DC converter and discussed the desirable properties ofthe converter and the challenges involved.Chapter 2 presented the previous strategies used by researchers to develop bi-directionalDC-DC converters for use in hybrid energy storage systems. It also discussed the strategiesto reduce inductor size and maximize the converters power density.Chapter 3 proposed the use of a four-level two-phase converter which allows the useof significantly smaller passive filter components and more efficient low voltage GaN62switches, improving power density and efficiency. It also provided a stress analysis andproposed real component part numbers which matched the design parameters and stresses.It concluded by proposing a novel startup method to pre-charge all converter capacitors,making the use of multi-level converters feasible for bi-directional operation.Chapter 4 presented the simulation results of the 4L2P topology and compared it to asimilarly designed half bridge topology. It also compared the estimated power densitiesand efficiencies of the converters. The proposed startup method was also simulated andverified to work effectively.5.3 Future WorkThis section presents potential future work that could help improve the design.5.3.1 Prototype Testing and Re-DesignA prototype was designed, built and tested, however due to issues with the GAN devicesin a multilevel configuration the converter was unable to function at its designed high volt-age input without failing. Further investigation is required to achieve full functionality andperformance. The likely cause is due to parasitic inductance of the PCB in combinationwith insufficient decoupling capacitors, causing excessive ringing on the floating grounds,which cause false triggering of the gate drivers, resulting in a short circuit between the syn-chronous switches causing failure. Potential solutions include adding more low inductance,low capacitance ceramic capacitors to help with decoupling. Another potential solution isto use a gate driver with ground noise protection which can prevent false triggering.As the issues are likely at least partially due to the PCB design, a new PCB will needto be designed. The current PCB design is based off the schematic in Appendix A and isavailable in Appendix D. The current board design is a 4 layer PCB with 2 oz copper onthe top and bottom layer and 1 oz copper in the middle layers. The layout was designed to63minimize the loop inductance between the switches and between the switches and the gatedrivers, however increasing copper thickness (3oz) and optimizing the layout could helpfurther minimize parasitic inductance and maximize efficiency. The current layout is alsooptimized for maximum power density as space and weight are important factors, howeversome changes would be necessary to make the design easier to manufacture, includingmaking the FCs non stacked and possibly reducing the number of components mounted onthe back of the board.Once the issues are corrected the converter should be fully tested for performance acrossthe full load and duty cycle ranges and tested for bi-directionality. After this the startupsequence and controller could be tested for their real world performance and functionality.5.3.2 Efficiency OptimizationSince the 4-Level topologies inductor current ripple varies with duty cycle, there is a po-tential opportunity to vary the frequency of the converter with respect to duty cycle andripple current to optimize the losses. This strategy could potentially increase the averageefficiency of the converter over the full range of operation for HESS applications and reducethe size and cost of cooling components and or increase the reliability of the converter.64Bibliography[1] McKinsey & Company. Boost! Transforming the powertrain value chain a portfoliochallenge. page 22, 2011. → page 1[2] J. Vetter, P. Nova´k, M. R. Wagner, C. Veit, K. C. Mo¨ller, J. O. Besenhard, M. Winter,M. Wohlfahrt-Mehrens, C. Vogler, and A. Hammouche. Ageing mechanisms inlithium-ion batteries. 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Inductor design with magnetics powder cores. → page 3168Appendix A4-Level 2 Phase DC-DC ConverterSchematic691122334455667788DDCCBBAATitleNumberRevisionSize A2Date:03/08/2018Sheet ofFile:C:\Users\..\4LevelSchmRev2.SchDocDrawn By:EPC2034Q6EPC2034Q1EPC2034Q2EPC2034Q3EPC2034Q4EPC2034Q5ViGND10uHL11uFC4110uFC1910uFC20EPC2034Q12EPC2034Q7EPC2034Q8EPC2034Q9EPC2034Q10EPC2034Q11ViGND10uHL210uFC3910uFC40VoV+1GND2J1 VbatInV+1GND2J3 VcapinVbatVcapGNDGNDPhaseAPhaseBPhaseBPhaseAGND4.7uFC45V+1GND2J2 12Vin12VGND10R11R20.22uFC3Vdd11A12N/C3GND14GND25B16N/C7Vdd28Si8610U1Isolator5VGNDSW11uFC1D1VDD1IN-2IN+3OUTL4OUTH5VREF6GND7UCC27611U2Gate Driver1uFC210R31R40.22uFC6Vdd11A12N/C3GND14GND25B16N/C7Vdd28Si8610U3Isolator5VGNDSW21uFC4D2VDD1IN-2IN+3OUTL4OUTH5VREF6GND7UCC27611U4Gate Driver1uFC510R51R60.22uFC9Vdd11A12N/C3GND14GND25B16N/C7Vdd28Si8610U5Isolator5VGNDSW31uFC7D3VDD1IN-2IN+3OUTL4OUTH5VREF6GND7UCC27611U6Gate Driver1uFC810R71R80.22uFC12Vdd11A12N/C3GND14GND25B16N/C7Vdd28Si8610U7Isolator5VGNDSW41uFC10D4VDD1IN-2IN+3OUTL4OUTH5VREF6GND7UCC27611U8Gate Driver1uFC1110R91R100.22uFC15Vdd11A12N/C3GND14GND25B16N/C7Vdd28Si8610U9Isolator5VGNDSW51uFC13D5VDD1IN-2IN+3OUTL4OUTH5VREF6GND7UCC27611U10Gate Driver1uFC1410R111R120.22uFC18Vdd11A12N/C3GND14GND25B16N/C7Vdd28Si8610U11Isolator5VGNDSW61uFC16VDD1IN-2IN+3OUTL4OUTH5VREF6GND7UCC27611U12Gate Driver1uFC1712V10R131R140.22uFC21Vdd11A12N/C3GND14GND25B16N/C7Vdd28Si8610U14Isolator5VGNDSW71uFC23D6VDD1IN-2IN+3OUTL4OUTH5VREF6GND7UCC27611U13Gate Driver1uFC2210R151R160.22uFC24Vdd11A12N/C3GND14GND25B16N/C7Vdd28Si8610U16Isolator5VGNDSW81uFC26D7VDD1IN-2IN+3OUTL4OUTH5VREF6GND7UCC27611U15Gate Driver1uFC2510R171R180.22uFC27Vdd11A12N/C3GND14GND25B16N/C7Vdd28Si8610U18Isolator5VGNDSW91uFC29D8VDD1IN-2IN+3OUTL4OUTH5VREF6GND7UCC27611U17Gate Driver1uFC2810R191R200.22uFC30Vdd11A12N/C3GND14GND25B16N/C7Vdd28Si8610U20Isolator5VGNDSW101uFC32D9VDD1IN-2IN+3OUTL4OUTH5VREF6GND7UCC27611U19Gate Driver1uFC3110R211R220.22uFC33Vdd11A12N/C3GND14GND25B16N/C7Vdd28Si8610U22Isolator5VGNDSW111uFC35D10VDD1IN-2IN+3OUTL4OUTH5VREF6GND7UCC27611U21Gate Driver1uFC3410R231R240.22uFC36Vdd11A12N/C3GND14GND25B16N/C7Vdd28Si8610U24Isolator5VGNDSW121uFC38VDD1IN-2IN+3OUTL4OUTH5VREF6GND7UCC27611U23Gate Driver1uFC37IP+1IP+2IP-3IP-4GND5VZCR6VIout7Vcc8ACS730U26IP+1IP+2IP-3IP-4GND5VZCR6VIout7Vcc8ACS730U25GNDGNDIPAIPB5V5VV33D-ISO1RX-RS2322N/A3N/A4N/A5GND_ISO6ADCIN-B07GND8ADCIN-B19GND10ADCIN-B211GND12ADCIN-B313GND14ADCIN-B415N/A16ADCIN-B517GPIO-5818ADCIN-B619GPIO6020ADCIN-B721GPIO6222PWM1A23PWM2A24PWM3A25PWM4A26GND27PWM5A28PWM6A29GPIO4830GPIO8431GPIO8632GPIO1233GPIO1534GPIO2435GPIO2636GND37GPIO1638GPIO1839GPIO2040GPIO2241GPIO8742GPIO2843GPIO3044GPIO3245GPIO3446GND47TCK48TMS49EMU150V33D-ISO51TX-RS23252N/A53N/A54N/A55GNS_ISO56ADCIN-A057GND58ADCIN-A159GND60ADCIN-A261GND62ADCIN-A363GND64ADCIN-A465N/A66ADCIN-A567GPIO5968ADCIN-A669GPIO6170ADCIN-A771GPIO6372PWM1B73PWM2B74PWM3B75PWM4B76+5V in77PWM5B78PWM6B79GPIO4980GPIO8581+5V in82GPIO1383GPIO1484GPIO2585GPIO2786+5V in87GPIO1788GPIO1989GPIO2190GPIO2391+5VIn92GPIO2993GPIO3194GPIO3395+5V in96TDI97TDO98TRSTn99EMU0100U28F28335 Control CardTMS1TDI3VCCS5TRST2GND4NC6TDO7GND8RTCK9GND10TCK11GND12EMU013EMU114J4 JTAG connectorGNDGNDGNDGNDGNDGNDGNDGNDGNDGNDGNDGND5V 5V 5V5V5VTMSTDI5VTDORTCKTCKEMU0EMU1TRSTTMSTCKEMU1TDITDOTRSTEMU0SW1SW6SW2SW5SW3SW4SW7SW12SW8SW11SW9SW10IPAIPB1MR25Res18kR26Res1GNDTX1GND2RX3J5 sciGNDRxTxTxRxVin1Vout2GND3U29LDO5VGND4.7uFC49Cap4.[binary]-SPSTVoVcapVbatViGND10R41Res1ViGNDVset-Vreset-12VK1relayVset-Vreset-12VK2relayQ15MOSFET-NQ16 MOSFET-NQ14 MOSFET-NQ13MOSFET-NQ17MOSFET-NGNDGNDGNDGND12V12V12VHVrelSetHVrelResetLVrelResetLVrelSetSSrelHVrelSetHVrelResetLVrelSetLVrelResetSSrelTPTP1TPTP2TPTP3TPTP4 TPTP5TPTP6TPTP7 TPTP8TPTP9TPTP10 TPTP11TPTP12TPTP13TPTP14TPTP15TPTP16TPTP17TPTP18TPTP19TPTP20TPTP21TPTP22TPTP23TPTP24TPTP25TPTP26TPTP27TPTP28 TPTP29 TPTP30 TPTP31 TPTP32 TPTP33TPTP34TPTP35TPTP36TPTP37TPTP38TPTP39TPTP42 TPTP43TPTP44TPTP45TPTP46TPTP47TPTP48TPTP49TPTP50TPTP51TPTP52TPTP53TPTP54TPTP55TPTP561uFC421uFC431uFC444.7uFC461uFC471uFC481MR42Res18kR43Res1GNDViLVViLVi240Vi240Vi240Vi360Vi360V i360Vi360Vi360V i360Vi360Vi240Vi360Vi360Vi360Vi360Vi360Vi360Vi240Vi240Vi120Vi120Vi120Vi120ViLViLViLVGNDi LVi LVi LVi LVi LVi LVi LVi LVi LVi LVi LVi LVi LVi LViLVi LV i LViLViLViLViLViLViLViLViLViLViLViLViLViLViLViLViLViLViLViLViLViLViLV iLViLViLV i LVi120V i120Vi120Vi120V i120Vi240V i240Vi240V i240Vi240Vi360V i360Vi360Vi360V i360Vi360V i360Vi360V i360Vi360Vi360Vi360Vi360V i360Vi360Vi360Vi360V i360Vi360V i360V i360V i360Vi360V i360Vi360Vi360V i360Vi360V i360Vi360Vi240V i240Vi240V i240Vi240Vi120V i120Vi120V i120Vi120ViLViLViLV i LViLV12Vi360VVC39i LViLVi360Vi360Vi360VV+1GND2J7 FanConV+1GND2J8 FanCon12V12VGNDGNDi360Vi360Vi360Vi240Vi120Vi120Vi240Vi360Vi360Vi360VTPTP40TPTPTP41TPiLVF1 Fuse 2F2 Fuse 24.7uFC51CapGND2kR44Res12kR45Res12kR47Res12kR48Res1GNDGNDGNDGNDD11TranzorbGNDD12D ZenerD13D ZenerD14D ZenerD15D ZenerD16D ZenerD17D ZenerGNDGNDGNDGNDGNDGNDD18D ZenerD19D ZenerGNDGNDD20TranzorbGNDS1 SW-SPSTA1K2D21LED0200R49Res1GNDLVrelReset2kR50Res1GNDTPCPUPIC101 PIC102 COC1 PIC201 PIC202 COC2 PIC301 PIC302 COC3 PIC401 PIC402 COC4 PIC501 PIC502 COC5 PIC601 PIC602 COC6 PIC701 PIC702 COC7 PIC801 PIC802 COC8 PIC901 PIC902 COC9 PIC1001 PIC1002 COC10 PIC1101 PIC1102 COC11 PIC1201 PIC1202 COC12 PIC1301 PIC1302 COC13 PIC1401 PIC1402 COC14 PIC1501 PIC1502 COC15 PIC1601 PIC1602 COC16 PIC1701 PIC1702 COC17 PIC1801 PIC1802 COC18 PIC1901 PIC1902 COC19 PIC2001 PIC2002 COC20 PIC2101 PIC2102 COC21 PIC2201 PIC2202 COC22 PIC2301 PIC2302 COC23 PIC2401 PIC2402 COC24 PIC2501 PIC2502 COC25 PIC2601 PIC2602 COC26 PIC2701 PIC2702 COC27 PIC2801 PIC2802 COC28 PIC2901 PIC2902 COC29 PIC3001 PIC3002 COC30 PIC3101 PIC3102 COC31 PIC3201 PIC3202 COC32 PIC3301 PIC3302 COC33 PIC3401 PIC3402 COC34 PIC3501 PIC3502 COC35 PIC3601 PIC3602 COC36 PIC3701 PIC3702 COC37 PIC3801 PIC3802 COC38 PIC3901 PIC3902 COC39 PIC4001 PIC4002 COC40 PIC4101 PIC4102 COC41 PIC4201 PIC4202 COC42 PIC4301 PIC4302 COC43 PIC4401 PIC4402 COC44 PIC4501 PIC4502 COC45 PIC4601 PIC4602 COC46 PIC4701 PIC4702 COC47 PIC4801 PIC4802 COC48 PIC4901 PIC4902 COC49 PIC5001 PIC5002 COC50 PIC5101 PIC5102 COC51 PICPU01 COCPU PID101 PID102 COD1 PID201 PID202 COD2 PID301 PID302 COD3 PID401 PID402 COD4 PID501 PID502 COD5 PID601 PID602 COD6 PID701 PID702 COD7 PID801 PID802 COD8 PID901 PID902 COD9 PID1001 PID1002 COD10 PID1101 PID1102 COD11 PID1201 PID1202 COD12 PID1301 PID1302 COD13 PID1401 PID1402 COD14 PID1501 PID1502 COD15 PID1601 PID1602 COD16 PID1701 PID1702 COD17 PID1801 PID1802 COD18 PID1901 PID1902 COD19 PID2001 PID2002 COD20 PID2101 PID2102 COD21 PIF101 PIF102 COF1 PIF201 PIF202 COF2 PIJ101 PIJ102 COJ1 PIJ201 PIJ202 COJ2 PIJ301 PIJ302 COJ3 PIJ401 PIJ402 PIJ403 PIJ404 PIJ405 PIJ406 PIJ407 PIJ408 PIJ409 PIJ4010 PIJ4011 PIJ4012 PIJ4013 PIJ4014 COJ4 PIJ501 PIJ502 PIJ503 COJ5 PIJ701 PIJ702 COJ7 PIJ801 PIJ802 COJ8 PIK101 PIK102 PIK103 PIK104 PIK105 COK1 PIK201 PIK202 PIK203 PIK204 PIK205 COK2 PIK301 PIK302 PIK303 PIK304 COK3 PIL101 PIL102 COL1 PIL201 PIL202 COL2 PIQ101 PIQ102 PIQ103 COQ1 PIQ201 PIQ202 PIQ203 COQ2 PIQ301 PIQ302 PIQ303 COQ3 PIQ401 PIQ402 PIQ403 COQ4 PIQ501 PIQ502 PIQ503 COQ5 PIQ601 PIQ602 PIQ603 COQ6 PIQ701 PIQ702 PIQ703 COQ7 PIQ801 PIQ802 PIQ803 COQ8 PIQ901 PIQ902 PIQ903 COQ9 PIQ1001 PIQ1002 PIQ1003 COQ10 PIQ1101 PIQ1102 PIQ1103 COQ11 PIQ1201 PIQ1202 PIQ1203 COQ12 PIQ1301 PIQ1302 PIQ1303 COQ13 PIQ1401 PIQ1402 PIQ1403 COQ14 PIQ1501 PIQ1502 PIQ1503 COQ15 PIQ1601 PIQ1602 PIQ1603 COQ16 PIQ1701 PIQ1702 PIQ1703 COQ17 PIR101 PIR102 COR1 PIR201 PIR202 COR2 PIR301 PIR302 COR3 PIR401 PIR402 COR4 PIR501 PIR502 COR5 PIR601 PIR602 COR6 PIR701 PIR702 COR7 PIR801 PIR802 COR8 PIR901 PIR902 COR9 PIR1001 PIR1002 COR10 PIR1101 PIR1102 COR11 PIR1201 PIR1202 COR12 PIR1301 PIR1302 COR13 PIR1401 PIR1402 COR14 PIR1501 PIR1502 COR15 PIR1601 PIR1602 COR16 PIR1701 PIR1702 COR17 PIR1801 PIR1802 COR18 PIR1901 PIR1902 COR19 PIR2001 PIR2002 COR20 PIR2101 PIR2102 COR21 PIR2201 PIR2202 COR22 PIR2301 PIR2302 COR23 PIR2401 PIR2402 COR24 PIR2501 PIR2502 COR25 PIR2601 PIR2602 COR26 PIR2701 PIR2702 COR27 PIR2801 PIR2802 COR28 PIR2901 PIR2902 COR29 PIR3001 PIR3002 COR30 PIR3101 PIR3102 COR31 PIR3201 PIR3202 COR32 PIR3301 PIR3302 COR33 PIR3401 PIR3402 COR34 PIR3501 PIR3502 COR35 PIR3601 PIR3602 COR36 PIR3701 PIR3702 COR37 PIR3801 PIR3802 COR38 PIR3901 PIR3902 COR39 PIR4001 PIR4002 COR40 PIR4101 PIR4102 COR41 PIR4201 PIR4202 COR42 PIR4301 PIR4302 COR43 PIR4401 PIR4402 COR44 PIR4501 PIR4502 COR45 PIR4701 PIR4702 COR47 PIR4801 PIR4802 COR48 PIR4901 PIR4902 COR49 PIR5001 PIR5002 COR50 PIS101 PIS102 COS1 PITP101 COTP1 PITP201 COTP2 PITP301 COTP3 PITP401 COTP4 PITP501 COTP5 PITP601 COTP6 PITP701 COTP7 PITP801 COTP8 PITP901 COTP9 PITP1001 COTP10 PITP1101 COTP11 PITP1201 COTP12 PITP1301 COTP13 PITP1401 COTP14 PITP1501 COTP15 PITP1601 COTP16 PITP1701 COTP17 PITP1801 COTP18 PITP1901 COTP19 PITP2001 COTP20 PITP2101 COTP21 PITP2201 COTP22 PITP2301 COTP23 PITP2401 COTP24 PITP2501 COTP25 PITP2601 COTP26 PITP2701 COTP27 PITP2801 COTP28 PITP2901 COTP29 PITP3001 COTP30 PITP3101 COTP31 PITP3201 COTP32 PITP3301 COTP33 PITP3401 COTP34 PITP3501 COTP35 PITP3601 COTP36 PITP3701 COTP37 PITP3801 COTP38 PITP3901 COTP39 PITP4001 COTP40 PITP4101 COTP41 PITP4201 COTP42 PITP4301 COTP43 PITP4401 COTP44 PITP4501 COTP45 PITP4601 COTP46 PITP4701 COTP47 PITP4801 COTP48 PITP4901 COTP49 PITP5001 COTP50 PITP5101 COTP51 PITP5201 COTP52 PITP5301 COTP53 PITP5401 COTP54 PITP5501 COTP55 PITP5601 COTP56 PIU101 PIU102 PIU103 PIU104 PIU105 PIU106 PIU107 PIU108 COU1 PIU201 PIU202 PIU203 PIU204 PIU205 PIU206 PIU207 COU2 PIU301 PIU302 PIU303 PIU304 PIU305 PIU306 PIU307 PIU308 COU3 PIU401 PIU402 PIU403 PIU404 PIU405 PIU406 PIU407 COU4 PIU501 PIU502 PIU503 PIU504 PIU505 PIU506 PIU507 PIU508 COU5 PIU601 PIU602 PIU603 PIU604 PIU605 PIU606 PIU607 COU6 PIU701 PIU702 PIU703 PIU704 PIU705 PIU706 PIU707 PIU708 COU7 PIU801 PIU802 PIU803 PIU804 PIU805 PIU806 PIU807 COU8 PIU901 PIU902 PIU903 PIU904 PIU905 PIU906 PIU907 PIU908 COU9 PIU1001 PIU1002 PIU1003 PIU1004 PIU1005 PIU1006 PIU1007 COU10 PIU1101 PIU1102 PIU1103 PIU1104 PIU1105 PIU1106 PIU1107 PIU1108 COU11 PIU1201 PIU1202 PIU1203 PIU1204 PIU1205 PIU1206 PIU1207 COU12 PIU1301 PIU1302 PIU1303 PIU1304 PIU1305 PIU1306 PIU1307 COU13 PIU1401 PIU1402 PIU1403 PIU1404 PIU1405 PIU1406 PIU1407 PIU1408 COU14 PIU1501 PIU1502 PIU1503 PIU1504 PIU1505 PIU1506 PIU1507 COU15 PIU1601 PIU1602 PIU1603 PIU1604 PIU1605 PIU1606 PIU1607 PIU1608 COU16 PIU1701 PIU1702 PIU1703 PIU1704 PIU1705 PIU1706 PIU1707 COU17 PIU1801 PIU1802 PIU1803 PIU1804 PIU1805 PIU1806 PIU1807 PIU1808 COU18 PIU1901 PIU1902 PIU1903 PIU1904 PIU1905 PIU1906 PIU1907 COU19 PIU2001 PIU2002 PIU2003 PIU2004 PIU2005 PIU2006 PIU2007 PIU2008 COU20 PIU2101 PIU2102 PIU2103 PIU2104 PIU2105 PIU2106 PIU2107 COU21 PIU2201 PIU2202 PIU2203 PIU2204 PIU2205 PIU2206 PIU2207 PIU2208 COU22 PIU2301 PIU2302 PIU2303 PIU2304 PIU2305 PIU2306 PIU2307 COU23 PIU2401 PIU2402 PIU2403 PIU2404 PIU2405 PIU2406 PIU2407 PIU2408 COU24 PIU2501 PIU2502 PIU2503 PIU2504 PIU2505 PIU2506 PIU2507 PIU2508 COU25 PIU2601 PIU2602 PIU2603 PIU2604 PIU2605 PIU2606 PIU2607 PIU2608 COU26 PIU2801 PIU2802 PIU2803 PIU2804 PIU2805 PIU2806 PIU2807 PIU2808 PIU2809 PIU28010 PIU28011 PIU28012 PIU28013 PIU28014 PIU28015 PIU28016 PIU28017 PIU28018 PIU28019 PIU28020 PIU28021 PIU28022 PIU28023 PIU28024 PIU28025 PIU28026 PIU28027 PIU28028 PIU28029 PIU28030 PIU28031 PIU28032 PIU28033 PIU28034 PIU28035 PIU28036 PIU28037 PIU28038 PIU28039 PIU28040 PIU28041 PIU28042 PIU28043 PIU28044 PIU28045 PIU28046 PIU28047 PIU28048 PIU28049 PIU28050 PIU28051 PIU28052 PIU28053 PIU28054 PIU28055 PIU28056 PIU28057 PIU28058 PIU28059 PIU28060 PIU28061 PIU28062 PIU28063 PIU28064 PIU28065 PIU28066 PIU28067 PIU28068 PIU28069 PIU28070 PIU28071 PIU28072 PIU28073 PIU28074 PIU28075 PIU28076 PIU28077 PIU28078 PIU28079 PIU28080 PIU28081 PIU28082 PIU28083 PIU28084 PIU28085 PIU28086 PIU28087 PIU28088 PIU28089 PIU28090 PIU28091 PIU28092 PIU28093 PIU28094 PIU28095 PIU28096 PIU28097 PIU28098 PIU28099 PIU280100 COU28 PIU2901 PIU2902 PIU2903 COU29 PIC201 PIC501 PIC801 PIC1101 PIC1401 PIC1701 PIC5102 PID1102 PI5 PU28PIC1602 PIC4902 PID501 PID1001 PID2002 NLEMU0 NLEMU1 PIC202 PIC502 PIC802 PIC1102 PIC1402 PIC1601 PIC1702 PIC1801 PIC3601 PIC4101 PIC4201 PIC4301 PIC4501 PIC4601 PIC4701 PIC4801 PIC4901 PIC5001 PIC5101 PID1101 I3 P11ID0PID1601 PID1701 PID1801 PID1901 PID2001 PID2102 PIJ202 PIQ1203 PIQ1303 PIQ1403 PIQ1503 PIQ1603 PIQ1703 PIR2601 IR0PIR3401 IR0PIR3701 PIR4301 PIR4401 PIR4501 PIR4701 PIR5001 PIU1207 PIU2307 PI25 U205PIU2903 PIR5002 NLHVrelReset PIR4702 NLHVrelSet P12 NLIPA ID0R302R301NLIPB PIR4402 NLLVrelReset PIR4502 NLLVrelSet PIC101 PIC301 I00 PI103 PI202PR22PITP101 PIU207 PIC102 PID102 PIC302 PIC401 PIC601 PIQ03 PI302IR0PIU407 PIC402 PID101 PID202 PIC602 PIC702 PID201 PID302 PIC902 PIC1001 PIC1201 PIQ03 PIQ02 PIP41 PIU807 PIC1002 PID301 PID402 PIC1202 PIC1301 PIC1501 I00 PIU1007 PIC1302 PID401 PID502 PIC1502 PIC1802 P42 PIQ703 PIQ802 P32PI9 PIQ803 PIQ902 IR0PITP801 PIC3901 PIQ1003 PIQ1102 PITP1001 PIC3301 PIC4001 PIQ1103 PIQ1202 PIU2107 PIC3302 PIC3602 PIC5002 PIJ201 PIQ1301 PIQ1401 PIQ1501 PIQ1601 PIQ1701 P251 IU0PITP2801 PITP2901 PITP3001 PITP3101 PITP3201 PITP3301 PITP3401 R302IU0IU50PIC701 PIC901 PI303 PI402PIU607 PI5 P24 NLPhaseA PIQ903 PIQ1002 U01 I60 NLPhaseB NLRTCK NLRx NLSSrel NLSW1 PITP4501 NLSW2 PITP4601 NLSW3 PITP5201 NLSW4 PITP5101 NLSW5 NLSW6 PITP4701 NLSW7 PITP4901 NLSW8 PITP4801 NLSW9 NLSW10 PITP5401 NLSW11 NLSW12 NLTCK NLTDI NLTDO NLTMS NLTRST NLTx PITP1501 PID1802 NLVbatLV IR0 IR0NLVC19 I3 PIR2501 PR22NLVC20 ID0IR0 IR0NLVC39 P12PIR3301 P32NLVC40 PITP1401 PID1902 NLVcapLV PIC4502 PIC4602 PIC4702 PIC4802 PI102PIQ702 PIR4202 PITP1601 PIR4201 PIR4302 NLViLV PIC4102 PIC4202 PIC4302 70Appendix BBill of Materials for the 4-Level 2-PhaseDC-DC Converter and Half BridgeConverter71B.1 4-Level 2-Phase DC-DC converter Bill of MaterialsPart Number Description Designator Cost each Quantity Category Cost Section TotalISO7710FDR Digital Isolator U1 2.28 12 Bootstrap and Isolators 27.36RMCF0402JT100R Resistor 100 ohm R3, R4 0.007 24 Bootstrap and Isolators 0.168ES1D Bootstrap Diode D1 0.27 12 Bootstrap and Isolators 3.24CC0805KKX7R8BB105 1uF 20V Capacitor C2 0.134 12 Bootstrap and Isolators 1.608CL10A104KA8NNNC 0.1uF Capacitor C4 0.029 12 Bootstrap and Isolators 0.348 Bootstrap and Isolators32.724TMDSCNCD28335 DSP control card U1 100 1 Controller 100 Controller100EPC2034 200V GaN Switch Q1 9.93 12 GaN Switches 119.16 GaN Switches119.16UCC27611 GaN Gate Driver U2 3.63 12 Gate Driver & components 43.56RC0603JR-0710RL Resistor 10 ohm R1 0.025 12 Gate Driver & components 0.3RK73B1JTTD1R0J Resistor 1 ohm R2 0.009 12 Gate Driver & components 0.108EMK107B7224KA-T 0.22uF 16V Capacitor C3 0.039 12 Gate Driver & components 0.468CL10B105KA8NNNC 1uF 20V Capacitor C1 0.039 12 Gate Driver & components 0.468CZRU52C5V6 5.6V Zener Diode D3 0.38 12 Gate Driver & components 4.56 Gate Driver & components49.46455083 MPP Core L1, L2 12.35 2 Inductors 24.7 Inductors24.7ADJH23112 Startup Relay K2, K3 15.65 2 Other 31.3KT12-1A-40L-SMD Startup Relay K1 14.95 1 Other 14.95SMF512KJT Startup Resistor 12k R3, 1.27 1 Other 1.27ZLDO1117G50TA 12V to 5V fixed LDO U2 0.657 1 Other 0.657GRM21BR61E475MA12L 4.7uF LDO caps C6, C8 0.376 2 Other 0.752RE1C002UNTCLCT-ND MOSFET relay driver Q1, Q2, Q3, Q4, Q5 0.264 5 Other 1.32PJ-037A 12V connector J4 0.788 1 Other 0.788DESD5V0S1BL-7B 14V TVS diode D2 0.393 1 Other 0.393ERB-RE0R50V 500mA Fuse F1, F2 0.351 2 Other 0.702RMCF0603JT2K00 2k ohm 0603 resistorR4, R5, R6, R18, R19 0.009 5 Other 0.045DF2S6P2CTC 5.5V TVS diode D4 0.423 1 Other 0.423150060GS75000 Power LED indicator D7 0.2 1 Other 0.2RMCF0805JG470R 470 ohm resistor R13 0.031 1 Other 0.031G-105-0513 12V switch SW1 1.809 1 Other 1.80961300311121 3 pin con J2 0.127 1 Other 0.127CL21A106KAYNNNE 10uF Capacitor C2 0.142 1 Other 0.142PREC007DBAN-M71RC JTAG conn J3 0.634 1 Other 0.634 Other55.543C5750X7T2W105K250KE 1uF 450V ceramic cap C10, C11, C12, C13 6.11 4 Power Capacitors 24.44B32774P6475K000 4.7uF 630V caps C1, C3 3.7 2 Power Capacitors 7.4CKG57NX7T2J105M500JH 1uF 630V cap C4, C5 5.63 2 Power Capacitors 11.26CKG57NX7T2W225M500JH 2.2uF 450V ceramic cap C9, C14 5.63 12 Power Capacitors 67.56KRM55TR72E225MH01K 2.2uF 250V ceramic cap C7, C15 3.53 12 Power Capacitors 42.36 Power Capacitors153.02ACS730KLCTR?-40AB-T Current Sensor 50mV/A U3, U4 7.12 2 Sensors 14.24RT0805BRE071ML 1Meg 0.1% Resistor R20, R22, R23, R24 0.55 6 Sensors 3.3ERA-6AEB8061V 8k 0.1% Resistor R2, R8, R10, R12, R21, R25 0.467 6 Sensors 2.802RMC0805FT49K9 50k resistor R14, R16 0.01 2 Sensors 0.02RMC0805FT75K0 75k resistor R15, R17 0.01 2 Sensors 0.02 SensorsTotal Converter Cost 554.993 20.38272B.2 Half Bridge Bill of MaterialsPart Number Description Cost each Area Quantity Tot Area Category Cost Section TotalR1DX-0505/H-R 10V split DC-DC 6.71 1.63 2 3.26 Gate Driver & components 13.42WR06W2R00FTL 2 ohm res 0.06 0.013 2 0.026 Gate Driver & components 0.12CR0603-FX-10R0ELF 10 ohm res 0.03 0.013 2 0.026 Gate Driver & components 0.06ACPL-P346-000E opto/gate drive 6.07 0.44 2 0.88 Gate Driver & components 12.14PMEG4010CEH Diode 0.64 0.036 2 0.072 Gate Driver & components 1.28 Gate Driver & components27.02TMDSCNCD28335 DSP control card 100 8.05 1 8.05 Controller 100 Controller100GS66516T 650V 60A GaN 76.69 0.68 2 1.36 Switch 153.38 GaN Switches153.3855735 MPP Core 100 30.36 1 30.36 Inductors 100 Inductors100WR06X1800FTL 180 ohm res 0.06 0.013 2 0.026 Other 0.12RC0603FR-07130RL 130 ohm res 0.03 0.013 2 0.026 Other 0.06RC0603JR-0710RL 10 ohm res 0.06 0.013 2 0.026 Other 0.12RK73B1JTTD1R0J 1 ohm res 0.02 0.013 2 0.026 Other 0.04MCWR06X3301FTL 3.3k ohm res 0.06 0.013 7 0.091 Other 0.42C2012X5R1E475K125AB 4.7uF cap 25V 0.36 0.025 8 0.2 Other 2.88C1812C104KDRACTU 0.1uF cap 1kV 1.09 0.144 8 1.152 Other 8.72C0603C105K3RACTU 1uF cap 25V 0.33 0.013 4 0.052 Other 1.32ZLDO1117G50TA 12V to 5V fixed LDO 0.657 0.429 1 0.429 Other 0.657GRM21BR61E475MA12L 4.7uF LDO caps 0.376 0.025 2 0.05 Other 0.752BZX384C6V2-E3-08 6.2V zener 0.37 0.042 2 0.084 Other 0.74PJ-037A 12V connector 0.788 1.32 1 1.32 Other 0.788DESD5V0S1BL-7B 14V TVS diode 0.393 0.013 1 0.013 Other 0.393ERB-RE0R50V 500mA Fuse 0.351 0.013 2 0.026 Other 0.702RC0603FR-101KL 1k ohm res 0.03 0.013 2 0.026 Other 0.06DF2S6P2CTC 5.5V TVS diode 0.423 0.013 1 0.013 Other 0.423150060GS75000 Power LED indicator 0.2 0.013 1 0.013 Other 0.2RMCF0805JG470R 470 ohm resistor 0.031 0.013 1 0.013 Other 0.031G-105-0513 12V switch 1.809 0.781 1 0.781 Other 1.80961300311121 3 pin con 0.127 0.192 1 0.192 Other 0.127CL21A106KAYNNNE 10uF Capacitor 0.142 0.029 1 0.029 Other 0.142PREC007DBAN-M71RC JTAG conn 0.634 1 1 1 Other 0.634 Other20.378C5750X7T2W105K250KE 1uF 450V ceramic cap 6.11 0.2875 2 0.575 Power Capacitors 12.22B32778P6506K000 50uF 630V caps 15.88 20.125 3 60.375 Power Capacitors 47.64CKG57NX7T2J105M500JH 1uF 630V cap 5.63 0.2875 4 1.15 Power Capacitors 22.52B32774P6475K000 5uF 450V film cap 3.7 5.67 4 22.68 Power Capacitors 14.8 Power Capacitors97.18ACS781LLRTR-100B-T Current Sensor 13mV/A 8.15 0.41 1 0.41 Sensors 8.15RT0805BRE071ML 1Meg 0.1% Resistor 0.55 0.025 3 0.075 Sensors 1.65ERA-6AEB8061V 8k 0.1% Resistor 0.467 0.025 3 0.075 Sensors 1.401 Sensors134.962 Total Converter Cost 509.92 11.20173Appendix CFour Level Two Phase ConverterStart-up Sequence C Code741 f l o a t Vin1 = x1 ; / / B a t t e r y V o l t a g e2 f l o a t Vin2 = x2 ; / / Vin c a p a c i t o r v o l t a g e3 f l o a t Vout1 = x3 ; / / S u p e r c a p a c i t o r v o l t a g4 f l o a t c t r l D 1 =x4 ; / / c o n t r o l l e r du ty c y c l e o u t p u t phase A5 f l o a t c t r l D 2 =x5 ; / / c o n t r o l l e r du ty c y c l e o u t p u t phase B6 f l o a t I d e s =x6 ; / / The r e q u i r e d c u r r e n t / c u r r e n t r e f e r e n c e78 f l o a t RT=100; / / Relay s e t / r e s e t t ime 1=10 us s e t t o 100 sim 10000 p r o t o9 s t a t i c u n s i g n e d long i n t c t = 0 ; / / F r e e r u n n i n g t ime10 s t a t i c f l o a t dutyA = 0 . 5 ; / / M o d i f i a b l e du ty c y c l e phase A11 s t a t i c f l o a t dutyB = 0 . 5 ; / / M o d i f i a b l e du ty c y c l e phase B12 f l o a t I r e f =0 ; / / M o d i f i a b l e r e f e r e n c e c u r r e n t13 i n t c t r l E n =0; / / Enab le f o r c u r r e n t c o n t r o l l e r s1415 i n t R1 =0; / / Relay R1 d e s i r e d s t a t e16 i n t R2 =0; / / Relay R2 d e s i r e d s t a t e17 i n t R3 =0; / / Relay R3 d e s i r e d s t a t e18 s t a t i c i n t R2se t =0 ; / / Relay R2 s e t s t a t e19 s t a t i c i n t R 2 r e s e t =0 ; / / Relay R2 r e s e t s t a t e20 s t a t i c i n t R3se t =0 ; / / Relay R3 s e t s t a t e21 s t a t i c i n t R 3 r e s e t =0 ; / / Relay R3 r e s e t s t a t e2223 s t a t i c i n t R 2 s t a t e =0; / / keeps t r a c k o f c u r r e n t r e l a y s t a t e o f R224 s t a t i c i n t R 3 s t a t e =0; / / keeps t r a c k o f c u r r e n t r e l a y s t a t e o f R325 s t a t i c i n t ST =0; / / keeps t r a c k o f when R2 was s e t o r r e s e t26 s t a t i c i n t ST2 =0; / / keeps t r a c k o f when R3 was s e t o r r e s e t27 s t a t i c i n t PWMAen=0; / / D e t e r m i n e s i f PWMs of Phase A a r e e n a b l e d28 s t a t i c i n t PWMBen=0; / / D e t e r m i n e s i f PWMs of Phase B a r e e n a b l e d29 s t a t i c i n t f l a g =0; / / f l a g used t o p r e v e n t o s c i l a t i o n s betweens t a t e s30 s t a t i c i n t f l a g 2 =0; / / f l a g used t o p r e v e n t o s c i l a t i o n s betweens t a t e s31 s t a t i c i n t c o u n t =0 ; / / c o u n t e r used t o p roduce d e l a y s f o r r e a lp r o c e s s e s3233 f l o a t i n p u t V a r = 0 . 0 7 ; / / M u l t i p l e o f Vin b e f o r e r e l a y can c l o s e3435 c t ++; / / imcremen t s c u r r e n t t ime3637 / / P r e c h a r g e s a l l c o n v e r t e r c a p a c i t o r s , s t a g e 1 / 238 i f ( ( ( Vin1−Vin2 )>i n p u t V a r ∗Vin1 | | c t<RT∗0 . 9 9 ) && f l a g ==0)39 {40 / / Turn on p r e c h a r g e r e s i s t o r r e l a y41 R1 =1;42 R2 =0;43 R3 =0;4445 / / e n a b l e s bo th p h a s e s PWMs46 PWMAen=1;47 PWMBen=1;487549 i f ( Vout1 / Vin1 >0.05)50 {51 / / S e t s du ty c y c l e t o t h e r a t i o o f o u t p u t t o i n p u t v o l t a g e52 dutyA=Vout1 / Vin1 ;53 dutyB=dutyA ;5455 / / i n i t i a l l i z e s t h e c u r r e n t c o n t r o l l e r t o same du ty c y c l e56 i f ( c t r l D 1<dutyA && f l a g 2 ==0)57 {58 I r e f =60;59 c t r l E n =0;60 }61 e l s e62 {63 f l a g 2 =1;64 I r e f =0 ;65 c t r l E n =0;66 }67 }68 / / i f t h e r e i s l i t t l e o r no v o l t a g e on t h e SCs t h e min p r e c h a r g e du tyc y c l e i s s e t t o 0 . 0 569 e l s e70 {71 dutyA = 0 . 0 5 ;72 dutyB = 0 . 0 5 ;73 }74 }75 / / t u r n s on R2 and R3 and s e t I r e f t o 0 w h i l e r e l a y s s w i t c h and s t a r t sc o n t r o l l e r s t a g e 376 e l s e i f ( count<RT)77 {78 f l a g =1;79 R1 =1;80 R2 =1;81 R3 =1;8283 c o u n t ++;84 dutyA = c t r l D 1 ;85 dutyB = c t r l D 2 ;86 I r e f =0 ;87 c t r l E n =1;8889 PWMAen=1;90 PWMBen=1;91 }92 / / C o n v e r t e r goes i n t o normal c u r r e n t c o n t r o l l e d s t a t e , s t a g e 493 e l s e94 {95 R1 =0;96 R2 =1;97 R3 =1;769899 dutyA = c t r l D 1 ;100 dutyB = c t r l D 2 ;101 I r e f = I d e s ;102 c t r l E n =1;103104 PWMAen=1;105 PWMBen=1;106 }107108 / / c r e a t e s n e c e s s a r y p u l s e s f o r l a t c h i n g r e l a y R2109 i f ( R2 != R 2 s t a t e | | c t <(RT∗0 . 9 9 ) )110 {111 i f ( R2==1)112 {113 R2se t =1;114 R 2 r e s e t =0 ;115 }116 e l s e i f ( R2==0)117 {118 R 2 r e s e t =1 ;119 R2se t =0;120 }121 ST= c t ;122 R 2 s t a t e =R2 ;123 }124125 i f ( R2se t ==1 && ( ST+RT)>c t )126 {127 R2se t =1;128 R 2 r e s e t =0 ;129 }130 e l s e i f ( R 2 r e s e t ==1 && ( ST+RT)>c t )131 {132 R 2 r e s e t =1 ;133 R2se t =0;134 }135 e l s e136 {137 R2se t =0;138 R 2 r e s e t =0 ;139 }140141 / / c r e a t e s n e c e s s a r y p u l s e s f o r l a t c h i n g r e l a y R3142 i f ( R3 != R 3 s t a t e | | c t <(RT−2) )143 {144 i f ( R3==1)145 {146 R3se t =1;147 R 3 r e s e t =0 ;148 }77149 e l s e i f ( R3==0)150 {151 R 3 r e s e t =1 ;152 R3se t =0;153 }154 ST2= c t ;155 R 3 s t a t e =R3 ;156 }157158 i f ( R3se t ==1 && ( ST2+RT)>c t )159 {160 R3se t =1;161 R 3 r e s e t =0 ;162 }163 e l s e i f ( R 3 r e s e t ==1 && ( ST2+RT)>c t )164 {165 R 3 r e s e t =1 ;166 R3se t =0;167 }168 e l s e169 {170 R3se t =0;171 R 3 r e s e t =0 ;172 }173174 / / o u t p u t s n e c e s s a r y s i g n a l s175 y1=dutyA ;176 y2=dutyB ;177 y3=R1 ;178 y4= R2se t ;179 y5= R 2 r e s e t ;180 y6= R3se t ;181 y7= R 3 r e s e t ;182 y8=PWMAen;183 y9=PWMBen;184 y10= I r e f ;185 y11= c t r l E n ;18678Appendix DPrinted Circuit Board Design79D.1 Top Layer of the PCB80D.2 Second Layer of the PCB81D.3 Third Layer of the PCB82D.4 Bottom Layer of the PCB83
Thesis/Dissertation
eng
Electrical Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
A multilevel-multiphase DC-DC converter for use in battery-supercapacitor hybrid energy storage systems
Text