Optimized Resonant Converter by Implementing Shunt Branch Element as Magnetizing Inductance of Transformer in Electric Vehicle Chargers

Abstract

An optimized resonant converter with zero-voltage switching over an extensive range of loading is proposed to integrate renewable energy sources to an onboard charger. In conventional resonant circuit, high-frequency transformer (HF) parasitic components are used as tank circuit, this degrades the performance due to non-optimal magnetic components. Here, the HF transformer is fabricated with optimized resonant tank circuit shunt branch inductance ( $L_p$ ) as magnetizing inductance, hence eliminating the need for shunt branch inductance. The proposed resonant converter circuit design is optimized for minimum kilovoltampere rating and better voltage regulation with both duty cycle and frequency control (mixed control method). Furthermore, the performance of the converter at a very light load is improved using the proposed control method. Incorporating a low- $R_{\text{DS}}(\text{ON})$ silicon carbide mosfet and softly turning off the switches for a wide load variation minimizes conduction and switching losses and improves efficiency. Using powder core for the design of the tank circuit reduces magnetic losses. A 3-kW prototype of the converter is built to verify the performance from no load to full load. The highest efficiency of the proposed converter is 98.6%, attained at 50% full load.