Control of Three-phase Power Factor Corrected Rectifier in Balanced and Unbalanced Systems

Abstract

One-cycle Control is a unified constant-frequency control scheme, with which the three-phase rectifier achieves unity power factor and low THD. Previous research has been conducted on the OCC controlled rectifier in both balanced and unbalanced system. The analysis of the rectifier in unbalanced system indicates that although the controller is proposed for balanced system, it also works for the unbalanced system, and the phase currents will be proportional to the non-zero sequence phase voltages under unbalanced conditions. The result is satisfying since the current waveform quality is high and the source voltages have the same load stresses. However, there are still two limitations for the present OCC controller in unbalanced system: first, minimum switching losses can not be ensured, which is contradictory to the vector control goal; second, the present OCC controller will not be able to handle the extreme unbalanced system where one phase voltage is entirely zero. In light of these, this paper aims to improve the present OCC controller's performance in unbalanced system. By utilizing the non-zero sequence phase voltages for region selection, both limitations are eliminated. The proposed OCC vector controller can cope with all the system conditions, with switching losses always minimized. A 1kW experimental prototype has been built to verify the proposed controller.