A Novel Variable Impedance PM Machines With Separated Fault Tolerant Ring

This paper aims to analyze and design a novel variable impedance permanent magnet (PM) machine with separated fault tolerant ring. The proposed topology automatically changes from low impedance to ultra-high impedance under turn-to-turn short-circuit without complex fault diagnosis and control strategies. First, the topology and fault tolerance principle of the variable impedance PM machine are introduced. Then, a turn-to-turn short-circuit model considering the core saturation effect is developed for investigating the mechanism of fault tolerance performance improvement. It is found that the short-circuit current and torque ripple after the fault of the variable impedance machines are significantly lower than those of the conventional ones. Furthermore, a proportional relationship between the size of the fault tolerant ring and the anti-short-circuit performance is revealed. The short-circuit current suppression effect saturates as the weight increase ratio of the fault tolerant ring reaches 40%. Moreover, the proposed variable impedance machine combines high power density and strong fault tolerance by comprehensively comparing with the conventional high impedance machine. Finally, a prototype is built and tested to validate the analysis.