A new step-up DC/DC resonant converter with a capacitive output filter for medium voltage (MV) DC grid in wind energy power systems

A new step-up DC/DC resonant converter is proposed in this paper for medium voltage DC grid in offshore wind energy system. The proposed converter combines two modular Asymmetrical Pulse-Width Modulated (APWM) resonant circuits with four strings of switch pairs. These switches are arranged with two pairs of two switches connected to an APWM LCL resonant circuit. There are several features in the proposed converter: (1) the multi-string arrangement of the switches allows a voltage stress of only a quarter of the input voltage across each power transistor; (2) the two modular APWM LCL resonant circuits are able to achieve high voltage gain so that large turns ratio high frequency transformer is eliminated; (3) soft switching turn-on and off are achieved in all the switches to enhance the overall circuit efficiency. The regulation of the output voltage is performed by controlling the duty cycle of the inner switch pair in the two resonant circuit modules. Results confirmed that an efficiency of at least 93.1 % is achieved on a 20kHz, 3.3kV_rms/40kV system for a wide range of load conditions.