A Novel Zero Sequence Current Suppression Scheme for Open-Winding Permanent Magnet Synchronous Motor Based on Model-Free Control

In open-winding permanent magnet synchronous motors (OW-PMSMs) with a single dc bus, zero sequence current (ZSC) would cause unwanted power loss and negatively affect stability of the system, so it should be addressed. In this article, an improved control scheme is proposed, which can maintain good ZSC performance under varying conditions and reduce the switching action times synchronously. First, an extended state observer that can predict the next instant ZSC and calculate the next instant desired zero sequence voltage (ZSV) is established. In this process, the model-free control principle is applied, which overcomes the problem of dependence on the zero-sequence loop parameters. Second, to reduce the switching frequency in traditional equal distribution modulation strategy, a novel modulation method is illustrated. Zero voltage vector is avoided, and the dwell time of active voltage vectors is redistributed to generate the desired ZSV. As a result, the times of switching actions has reduced from 12 to 8, and this reduction in switching actions is accompanied by effective suppression of ZSC. Finally, to test the effectiveness of the proposed method, several experimental results obtained using existing methods and the proposed method are presented.