A Control Technique for Achieving ZVS and Minimum Conduction Loss in DAB by Varying Input DC Link Voltage for EV Applications

Isolated DC-DC converters are essential in electric vehicle (EV) applications. For power ratings exceeding 5kW, the Dual Active Bridge (DAB) converter is often preferred due to its lower conduction losses than resonant converters. However, DAB converters suffer from higher switching loss, particularly under light load conditions which adversely affects system efficiency. The wide voltage variation in EV batteries makes it challenging to maintain the DAB's voltage gain within the ZVS range when the turns ratio is fixed. This paper proposes a control technique for a DAB converter that maintains the voltage gain ratio within the ZVS range, even under light load conditions, while also minimizing conduction losses. A comprehensive loss analysis of a 6.6kW DAB converter is conducted across various DC link input voltages for EV charging applications. The analysis covers an output voltage range of 300-500V. The study demonstrates that maintaining a voltage gain ratio near unity is crucial for achieving ZVS and minimizing conduction losses. Further, also explores the relationship between battery voltage variations and the corresponding optimal input DC link voltage to reduce switching and conduction losses and is carried out using the PLECS Blockset integrated with MATLAB/Simulink.