A Matrix-Based Nonisolated Three-Phase AC–DC Rectifier With Large Step-Down Voltage Gain

Abstract

This paper presents a matrix-based nonisolated three-phase ac–dc converter with a current-doubler rectifier (CDR) circuit. Buck-type rectifiers are normally used for step-down ac-to-dc conversion. However, for three-phase buck rectifiers, the lower bound of rectified dc voltage is limited as the converter is severely underutilized by operating at lower modulation index. Moreover, at lower modulation index, the rms values of current increases contributing to higher conduction losses. However, by using a matrix (3 × 1) topology followed by a CDR, the desired dc output voltage can be reduced by half. The matrix topology directly converts three-phase line frequency ac voltages into intermediate high-frequency ac voltage which is subsequently, rectified using a CDR to obtain the required output dc voltage. A modified space vector modulation based modulation scheme especially suited for the proposed converter is presented for superior input power quality with reduced power loss. Comprehensive analysis and design of the proposed converter is carried out followed by simulation and laboratory-based experimental tests. Subsequently, the loss analysis of the proposed converter is carried out and a comparative evaluation of the proposed converter with the traditional six-switch buck rectifier is provided to demonstrate the suitability of the proposed converter for large step-down voltage gain. Digital implementation of the proposed modulation scheme is carried out at 40-kHz switching frequency. A hardware prototype of 500 W is developed to validate the theoretical and simulation results.