Analysis of Winding-Connection Sequence in Multiphase Series-End Winding Motor Drives for Leg-Current Stress Reduction

Series-end winding motor drives (SWMDs) are more well known for the characteristics of high dc-link voltage utilization and controllable zero-sequence loop. Besides, SWMDs also have the potential ability to reduce the leg-current stress (LCS) by rearranging the winding-connection sequence (WCS), especially in multiphase SWMDs (MP-SWMDs). Yet, this characteristic is not widely noticed in the existing works. To this end, this article presents the analysis of WCS in MP-SWMDs for LCS reduction, which provides the possibility to improve the load capability and reliability compared with the existing WCS. Based on the phasor diagrams of the leg- and phase-currents, the principle of the WCS in MP-SWMDs for LCS reduction is revealed, which is discussed separately for the symmetrical and asymmetrical (multiple three-phase) phase-windings. By rearranging the WCS and reversing part of windings in MP-SWMDs, optimal WCSs for LCS reduction are derived accordingly. Subsequently, the corresponding modulation schemes based on the relative potential are developed. Moreover, the linear modulation ranges of different WCSs in MP-SWMDs are also investigated. With the verification of the experimental results, the current amplitude of middle legs in MP-SWMDs under the optimal WCS for LCS reduction can be reduced significantly compared with the star-connected winding counterparts. Simultaneously, the linear modulation range is also reduced, which indicates that MP-SWMDs under the optimal WCS for LCS reduction are ideal for low- or medium-speed motor drives with heavy load.