Abstract
In this paper, a control method to improve ac input current waveforms of current type PWM rectifiers which has been proposed by the present authors is investigated. In this control strategy, state feedback of the ac side LC filter is introduced to eliminate waveform distortion and transient oscillation of input current of the rectifier. Theoretical investigation is made on the basis of equivalent circuits of the ac side of the rectifier which are derived in this paper. The function of the proposed feedback control is analyzed from the view point of the power flow between the LC filter and the bridge circuit of the rectifier.
From the results of the analysis, it is shown that the proposed control strategy provides damping effect in the form of equivalent resistance connected in parallel with the filter capacitor. The waveform distortion and transient oscillation of the input current are suppressed by this damping effect. On the basis of these results, a brief comparison between the improvement mechanism of the input current waveform by the proposed feedback control and that by active power filters is made. The effects of the feedback gain, control delay, and the circuit parameters of the LC filter on the elimination of harmonic current and on the stability of operation are investigated in detail. Analytical results shown in this paper are confirmed by computer simulation and experimental investigation.
