Reconfigurable fixed-frequency resonant converter with extended voltage gain for ultra-wide output range applications

Abstract This paper presents a universal series-resonant converter with an ultra-wide output voltage range for electric vehicle charging applications. The proposed converter is based on a unified two-state reconfigurable secondary-side structure in which the transformer secondary winding and rectifier stage operate in a coordinated manner. By simultaneous reconfiguration of the transformer secondary and rectifier structure across two operating modes, coarse voltage-gain steps are achieved. To bridge the gaps between these discrete steps, a boost converter is integrated with the resonant inverter. Through this integration, inverter duty cycle variation affects both the width and amplitude of the square waveform generated by the inverter, unlike conventional inverters where duty cycle variation primarily affects only the pulse width. This enhanced modulation capability increases the influence of duty cycle on voltage gain and enables fine regulation under fixed-frequency PWM control. The integration is realized without increasing the primary-side component count. The converter operates at the resonant frequency of the series network, ensuring reduced circulating currents, optimized component sizing, and simplified control, while maintaining a load-independent voltage gain characteristic. Zero-voltage-switching (ZVS) and zero-current-switching (ZCS) are achieved under all operating conditions. A 400 W laboratory-scale prototype with 380 V input, 50–400 V output, and 200 kHz switching frequency using SiC devices validates the proposed concept, achieving an overall voltage gain range of 1 to 8 under fixed-frequency PWM operation.