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 for high reliability applications. 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 of the variable impedance PM machine is introduced. Then, the magnetic field distribution of the separate fault tolerant ring under health and fault is analyzed to qualitatively reveal the fault tolerance principle. Finally, 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.