DESIGNING OF 6.6KW ON-BOARD CHARGER

Abstract

While designing any converter the cost, efficiency, and power density are taken into consideration. By considering the above points and industry requirements, the Three-Phase Active Front End Converter (AFEC) is chosen as the AC-DC converter, a Dual Active Bridge (DAB) Converter is chosen as the main DC-DC converter to charge the main battery of the vehicle, and an LLC resonant converter is chosen as the auxiliary DC-DC converter to charge auxiliary battery. However, DAB converters suffer from higher switching loss, particularly under light load conditions which adversely affects efficiency. The wide voltage range of EV batteries makes it complicated to maintain a voltage gain ratio of DAB under the ZVS range once the turns ratio is fixed. This thesis proposes a controlling technique for a DAB converter to maintain a voltage gain ratio under ZVS achieving range even in light load conditions while also achieving reduced conduction loss. A detailed loss analysis of a 6.6kW DAB converter was done at various DC link input voltages for EV charging applications with an output voltage range of 300-500V using PLECS BLOCKSET integrated within MATLAB/Simulink. The study demonstrates that maintaining a voltage gain ratio near unity is crucial for achieving ZVS and minimizing conduction losses. It also explores the relationship between battery voltage variations and the corresponding optimal input DC link voltage to reduce switching and conduction losses. Along with DAB, the LLC resonant converter is implemented and loss analysis is done for fixed input voltage in the PLECS simulation tool.