Investigation of Harmonic Currents and Power Factor on Power Rectifier Circuitwith Nonequi-PWM•Equi-PWMControl (Inductive Load)

Abstract

Lately, on the power rectifier circuit with semiconductor switching device, PWM control is generally employed for the purposes of reducing the harmonic currents on the DC side and improving the power factor of fundamental wave. In this case, the analysis of the current waveform becomes fairly complex. However, we express the PWM controlled voltage waveform by the step function, and can easily analyze the current waveform. We reported formerly some results of analysis about the waveform and harmonics of the current. In this paper, on the power rectifier circuit to which the nonequi-PWM and equi-PWM control are applied, we exactly calculate the harmonic currents on the DC and AC side, and the power factor by the use of the above analytical results. Thecharacteristics of both control methods are compared on condition that each controlled factor of the load voltage is equal. These results are shown in the calculated charts. The following items can be seen from these charts on the power rectifier circuit:
(1) The nonequi-PWM control can let the harmonic currents on the DC side decrease more than the equi-PWM control. But on the contrary, the harmonic currents on the AC side increase. Consequently, when the nonequi-PWM control is applied, the total power factor decreases by the increase of distortion factor of the current on the AC side.
(2) The difference between the harmonic currents on the DC and AC side to both of the nonequi-PWM and equi-PWM control increases with the increase of controlled factor of the load voltage.