Research on the filters used in the PWM VSR

PWM VSR is widely used in different power equipments to depress the harmonic of the ac-side current and improve power factor. In this paper, the operating principle and the control scheme of the single phase PWM rectifiers are introduced firstly, P(proportion) controller is used in the ac current control loop to ensure the ac-side current track the current reference fast, the related equations are deduced in details. The filter in the ac-side current feedback link is absolutely necessary to eliminate the high-order harmonic mixed with the useful signal; if the filter is set incorrectly in the control block, it will cause the phase shift of the sample signals, and the relevant time delay in the feedback signals will not be neglectable, it will deteriorate the whole system, even make the system unstable. To eliminate 2nd harmonic signal in dc voltage, the traditional second-order low-pass filter is employed in many control schemes; a notch filter is presented in this paper, and comparative studies between the low-pass filter and notch filter are carried out. The notch filter can alleviate the 2nd harmonic signal in the dc voltage signal remarkably, so it will depress the 3rd harmonic component in the ac current reference, and it will maintain the ac-side input current of the PWM rectifier with less harmonic and higher power factor . Due to that the notch filter doesn´t affect other band signals; it will not worsen the dynamic response of the whole system. At last, the conclusion is verified by simulation results. A 4.5 KVA prototype is constructed, and the related experiment results testify the analysis in the paper.