電流形PWM整流回路における入力電流ひずみと過渡振動に関する一考察

抄録

In current type PWM rectifiers which can realize unity power factor and almost sinusoidal ac input current, an LC filter is required on the ac side for the absorption of the carrier harmonics and voltage spikes due to the PWM operation. However, the LC filter may cause waveform distortion and transient oscillation of the ac input current.
In this paper, the ac input current waveform is analyzed quantitatively. From the analysis, the amplification effect of the LC filter on the harmonic currents is clarified. An expression for the prediction of the transient oscillation is derived. It is shown by the expression that the transient oscillation can contain an unbalanced harmonic component whose frequency is equal to the resonant frequency of the LC filter regardless of the ratio of the resonant frequency to fundamental frequency of the power supply.
From the results of these analysis, a method of selecting the resonant frequency of the LC filter to avoid the steady state harmonic distortion of the supply current is proposed. It is also clarified that conventional methods of improving ac input current waveform such as optimization of the PWM pattern or introduction of the high carrier frequency operation do not have any effect on the reduction of the transient oscillation. In contrast to this, a control strategy introducing state feedback control of the LC filter proposed by the present authors is effective on the reduction of the transient oscillation.
The analytical results shown in this paper are confirmed by some results of computer simulation.