A new three-phase AC/DC high power factor soft-switched step-up converter with high gain rectifier modules for medium voltage grid in wind systems

Abstract

This paper presents a new single-stage AC/DC step-up soft-switched converter for medium voltage (MV) DC grid for wind energy systems. To achieve close-to-unity power factor, stepping up the voltage and reduce the number of conversion stages, a three-phase boost AC/DC rectifier and a high frequency step-up resonant converter with high gain rectifier modules are combined into a single-stage step-up converter. As a result, the proposed converter is capable to achieve very high voltage gain efficiently without using bulky high turns ratio step-up transformer. Soft switching operation is achieved by using multiple resonant circuit modules. The voltage stress of each power switch is also reduced to half of the DC-link voltage by using a series connection of two strings of switch pairs. In addition, the proposed converter is capable to regulate the output MV grid voltage by utilizing a combination of duty cycle and variable switching frequency control. Results are given on a 1.5MW, 690Vac/40kV system to highlight the merits of the proposed converter.