Analysis of Short-Circuit Current Automatic Suppression for Toroidal Winding PM Machines

Short-circuit faults in permanent magnet (PM) machines have consistently been a hindrance for safety-critical applications. However, short-circuit currents, especially turn-to-turn short-circuit currents, are difficult to detect and suppress in a timely manner. This article investigates the automatically variable impedance characteristics of the toroidal winding, which restricts the turn-to-turn short-circuit current to an allowable level without terminal short circuit. An analytical model considering the saturation effect of toroidal winding is proposed to reveal the fault tolerance mechanism as well as the mapping relationship between yoke-annular-leakage and fault-tolerant performance. It is found that variable impedance PM machines with toroidal winding have superior fault tolerance performance compared to conventional fractional-slot concentrated-winding and lap winding. Besides, there is a contradictory relationship between its fault tolerance and electromagnetic performance. Furthermore, the laws of phase belt angle and pole number on the electromagnetic and fault-tolerant performance of toroidal winding are first presented in this article. The design criteria and the feasible pole-slot combinations that have inherent fault-tolerant capability are given. Finally, the prototype is built and tested. The experimental results match well with the analytical ones.