A Modular SiC-Based Step-Up Converter With Soft-Switching-Assisted Networks and Internally Coupled High-Voltage-Gain Modules for Wind Energy System With a Medium-Voltage DC-Grid

Abstract

In this paper, a fully soft-switched silicon carbide (SiC)-based modular step-up resonant converter with magnetically integrated zero current switching voltage doublers is proposed for medium-voltage (MV) dc conversion in wind energy systems. Conventional step-up resonant dc/dc converters employ either high turns-ratio step-up transformer or step-up resonant circuits to achieve step-up voltage conversion. As a result, they require either complicated expensive transformer structure due to high-voltage electrical isolation requirement or highly voltage-gain sensitive step-up resonant circuits, which are not ideal for designing MV converters for wind energy application. In order to solve the aforementioned drawbacks, the proposed converter configuration utilizes both modular step-up resonant circuits and magnetically integrated voltage doublers to achieve the step-up voltage conversion function. The output voltage of each module of the dc/dc step-up converter is regulated through variable frequency control, whereas asymmetrical pulsewidth modulation (APWM) control is utilized to balance all the resonant currents in all the resonant circuit modules in each converter module. Since APWM control is used, a simple passive auxiliary circuit is included in each converter module to extend soft-switching operation over a wide range of operating conditions. Simulation results on a 1-kV/28-kV, 5-MW converter system with commercial 1.2-kV SiC MOSFET modules and experimental results on a laboratory-scale 300-V/4.8-kV, 5.6-kW proof-of-concept prototype with commercial SiC MOSFET and SiC Schottky diodes are provided to validate the theoretical analysis and to highlight the merits of the proposed work.