A High Efficiency Wide Bandgap Transistor Based LCL-T DC-DC Converter for Charging EV Batteries of Wide Voltage Range

Abstract This paper introduces a bidirectional LCL-T power conversion topology that employs wide-bandgap semiconductor switches to achieve improved energy performance in electric vehicle battery charging applications with significant operating voltage variation. The converter operates at a relatively high frequency equal to the LCL-T resonant frequency to ensure reduced circuit magnetic component size, enhance circuit efficiency and obtain improved range of WBG transistor soft switching over the wide range of battery voltage variation. The LCL-T DC-DC converter, controlled at fixed input dc link voltage by an efficient phase angle shift modulation scheme on hand and then by input dc link voltage variation on the other hand, is first described and then analyzed using first harmonic approximation (FHA). The operational characteristics of a representative controlled LCL-T DC–DC converter are analyzed across a battery output voltage span of 150 V to 950 V, following a defined electric vehicle charging profile. For each mode of control (phase shift angle modulation at constant input dc link voltage OR input dc link voltage variation at zero shift phase angle in sympathy with the output battery voltage variation), the LCL-T DC-DC converter shows high efficiency values around 97%, improved range of transistor soft switching and easily controllable bidirectional capability.