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A new DSP controlled bi-directional DC/DC converter system for inverter/charger applications Swingler, Andrew Duncan

Abstract

As prices fall and performance increases DSP controllers are becoming increasingly attractive for use within switch mode power supply applications. However, due to the relative infancy of the technology questions remain concerning the practical implementation of DSP controlled power converters. This work is concerned with the application of current DSP hardware technology within a novel power electronic voltage converter system for combination inverter/chargers. Power circuit design, dynamic modeling, digital control and large signal computer simulation of a select 12:200 Volt, 400 Watt bi-directional dc/dc battery charge/discharge power-circuit are considered. Initially, a novel DSP interfaced bi-directional dc/dc power circuit for the selected inverter/charger application is proposed. The proposed power-circuit is novel in its seamless two-quadrant bilateral charge/discharge operation based on a single duty cycle control input and fixed pattern DSP derived synchronously rectified PWM switching. A prototype power-circuit is designed and evaluated experimentally with various semiconductor switch technologies. Ultimately the proposed concept is successfully proven using a combination of FET and IGBT high speed switching devices. To control the power-circuit a tri-mode digital control system is further developed to regulate the power-circuit in three modes of operation: bus voltage regulation, constant current charge regulation and constant battery voltage charge regulation. Small-signal plant models are derived from the non-linear power-circuit using a novel combination of state-space averaging and MATLAB analysis. To facilitate closed loop feedback controller design digitized both proportional integral (PI) and pure integral (I) feedback control compensators are derived using "worst-case operating point" plant models and frequency domain stability analysis. The pure I controller technique is ultimately adopted due to its proven performance and implementation ease as compared to the PI controller designs. To verify conceptually the system operation a novel MATLAB/SIMULINK based simulation method is developed to model the transient large signal behavior of the nonlinear power-circuit. This reliable simulation tool is shown to model the numerical effects of the DSP, confirm closed loop stability to large-signal changes in operating point and generally verify successful operation of the proposed tri-mode control approach. Finally, a prototype converter under closed loop DSP control is evaluated experimentally and its performance compared to the predicted results.

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