Inter-Turn Short Circuit Faults and Mitigation Measures for Dual-Three Phase Machines

Short circuits are a field-relevant fault type in electric motors and can impact their electrical, mechanical, and thermal behavior. This paper investigates the effects of different types of inter-turn short circuits (ITSCs) in interior permanent-magnet synchronous machines via simulation and testbench measurements. Depending on the severity of the ITSCs, various unfavorable effects can occur, including a decrease in average torque, an increase in torque ripple, asymmetry in electrical variables, or a significant rise in local current-induced heat losses. To prevent the fault from spreading and causing a complete system failure, fault mitigation strategies are necessary. These include switching the affected phase system to an active short circuit (ASC) or open circuit (OC). An alternative approach is to reduce the ITSC current through field weakening (FW), utilizing a higher d-current. The selection of an appropriate mitigation strategy is contingent upon the specific objective. OC minimizes overall copper losses, ASC reduces fault current and local losses, and active FW allows a balance between both requirements and enables a higher output torque.