Mitigation of harmonics in three-phase ac system using current injection technique for ac-to-dc converter

Abstract

This paper presents a new approach to eliminate harmonics and to improve power factor of a three phase front-end uncontrolled rectifier. A high-power-factor is achieved by injecting high-frequency triangular current from the output of three-phase inverter. The high frequency (HF) current modulates the rectifier input voltage resulting in conduction of diodes into each switching cycle. The resulting ac input line current is continuous and sinusoidal in shape with significant reduction in current harmonics. All the switches are operated at zero-voltage switching (ZVS). The diodes of the rectifier are also operated with soft switching at turn-on as well as at turn-off. Varying switching frequency with fixed duty ratio regulates the output voltage. The proposed ac-to-dc converter also maintains high-power-factor even for unbalanced input supply voltages. The analysis of the converter is carried out on a single-phase basis, using different operating modes in one switching cycle of injected current. Theoretical results based on analysis are verified initially through digital simulation, and confirmed by using an experimental prototype of 2.5 kW.