Zero-Sequence Current Elimination Strategy Based on Frequency-Adaptive Repetitive Control of OW Machines During Leg-Sharing Post-Fault Operation

Existing zero-sequence current (ZSC) elimination methods have unsatisfactory elimination performance during post-fault (PF) operation due to unequal dead time effects on the terminals of the open-end winding (OW) machine, resulting in a significant ZSC and unbalanced three-phase currents. This article proposes a new ZSC elimination strategy based on frequency-adaptive repetitive control (FARC) for OW machine drives to fully eliminate the ZSC during PF operation following inverter open circuit faults. In contrast to the traditional ZSC elimination methods, the proposed strategy can effectively eliminate the fundamental, triple, and additional frequency disturbances of the ZSC by only implementing ZSC closed-loop control. To this aim, a FARC based approach is proposed and designed to realize a zero steady-state tracking error of the ZSC loop by eliminating periodic disturbances that originate from both inverter and machine sides. Furthermore, a comprehensive analysis of the dead time effects on the ZSC during both healthy operation and PF operation is carried out. In addition, a decoupled space vector modulation technique is developed to produce the required zero-sequence voltage (ZSV) by unequally distributing the ZSC control signals of the legs of the two inverters within one duty cycle. Finally, the proposed strategy is verified via both simulations and experimentally on a dSPACE platform with an OW induction machine.