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UBC Theses and Dissertations

Implementing digital control to improve control bandwidth and disturbance rejection on a LLC resonant DC-DC power converter. Lei, Yubo

Abstract

In this thesis, the implementation of an adaptive digital control scheme and the development process to implement it for an existing analog controlled LLC resonant converter is presented. The goal is to improve the dynamic performance (aka control bandwidth) and the disturbance rejection ability of the closed loop system using digital control. A brief analysis of the experimented on LLC resonant converter and simulations of its control-to-output frequency response characteristics under different operating conditions are initially performed in order to show its non-linear behavior. Then the design process and requirements for both the digital and analog components to make the existing LLC converter compatible with a digital signal microcontroller is presented in detail. The digital signal microcontroller (DSC), ADC, DPWM, sampling period, interrupt service routine (ISR), and the 2P2Z digital compensator implementation will be overviewed. Analog components such as the voltage/current sensors, the VCO, and other analog interfacing components will also be presented. After that, the complete design process to achieve optimized digital compensators for several different operating points is presented. This design process introduces the method of using either the uncompensated loop-gain frequency response data collected empirically from the physical converter or from a PSIM simulation and then using MATLAB’s System Identification software toolbox to generate an estimated mathematical model based on frequency response data. A digital compensator is then designed based on the estimated mathematical model. A comparison between the PSIM simulation and the empirical data of the LLC converter’s plant frequency response for several different operating conditions is also presented. A digital adaptive compensator algorithm is implemented so that the most optimized compensator design for a given converter operating range is selected. The algorithm uses the output voltage and current to determine the operating point of the converter, which then access a software look-up-table (LUT) for the optimized compensator. A complete prototype is built to experimentally validate the digital design process and the performance results of a classical single compensator design is compared with the adaptive compensator design in order to show the benefits of the adaptive compensator control scheme.

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Attribution-NonCommercial-NoDerivs 2.5 Canada

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