The influence of no-load back electromotive force (EMF) of permanent magnet synchronous motor (PMSM) on power factor is analyzed. The mathematical models of the influence of the PMSM no-load back EMF on single-drive and multi-drive converters are established. The calculation results show that the converter with multi-drive structure can tolerate higher no-load back EMF of PMSM, and significantly improve the efficiency of the driving system.