High-power-factor operation with improved line current harmonics of three-phase AC-to-DC Converter

Most modern variable-speed motor drives are based on pulse width modulated voltage source inverters, supplied from a smooth DC link voltage. This is often obtained from a three-phase diode bridge mains rectifier with a large output capacitor to keep the DC link voltage essentially constant. The AC currents at the input of the bridge are often discontinuous and contain high levels of harmonics. Harmonic currents from non linear loads are unacceptable, as they penetrate the supply system and affect the voltage at the point of common coupling. In this paper a single stage, three-phase AC-to-DC converter topology, with new structure for high power applications is proposed. The principle features of the topology include continuous current operation of the input source inductors, inherent active wave shaping of the input currents, resulting in a high power factor operation. Only two active switches are required. Both the switches are soft-switched. The high frequency (HF) current injection technique is used. The diodes of rectifier also show soft-switching. The simulation results and experimental results for a laboratory prototype for 5 kW converter are presented.