DESIGN AND CONTROL OF VIENNA RECTIFIER FED FULL BRIDGE LLC RESONANT CONVERTER BASED TWO STAGE OFF-BOARD EV CHARGER WITH CC-CV CHARGING ALGORITHM

Abstract

This work has three objectives, first objective is designing and controlling of Vienna rectifier. In this objective a complete analysis of three phase Vienna rectifier considering the effect of parasitic in the system for off-board EV charging application is discussed. To improve the dynamic response a modified dual loop control using d-axis and q-axis current controller including the effect of system parasitic in control loops is proposed. The proposed algorithm is compared with different control algorithms viz., dual loop control using hysteresis current controller and dual loop control using d-axis and q-axis current controller with SVPWM. A comparative performance analysis is discussed in terms of dynamic response during system disturbances like load variation, reference DC bus voltage variation and grid side variations. A 50 kW Vienna Rectifier operating at a switching frequency of 200 kHz is used for performance evaluation of all three control algorithms and is validated using MATLAB-Simulink. The second objective is the designing of full bridge LLC resonant converter as well as designing of magnetics for high frequency transformer. In this objective voltage control of LLC resonant converter is designed using pulse frequency modulation (PFM) for controlling the output voltage and analyze the effect of load side and input side variations on the converter. In this, the input is constant 700V DC rather than the Vienna rectifier output to analyze the performance of the converter and it is validated using MATLAB-Simulink. The third objective combines all the analysis involved in first and second objective. In this objective a 50 kW two stage off-Board EV charger is designed for charging a lithium ion battery using constant current (CC)-constant voltage (CV) algorithm. First stage includes three phase Vienna rectifier with power factor correction. The output of the first stage is the DC bus, which acts as an input to the second stage. Second stage includes full bridge LLC resonant converter and a lithium ion battery is connected to the output of second stage. To maintain constant DC bus voltage of 700V and to ensure unity power factor, dual loop control using d-axis and q-axis current control using space vector pulse width modulation (SVPWM) is adopted for controlling Vienna rectifier. Closed loop control for full bridge LLC resonant converter is designed using CC-CV control algorithm and pulse frequency modulation (PFM) to charge the rated 280 V/112 Ah lithium ion battery. The designed system outcomes are validated using MATLAB-Simulink.