Influence of Dimensional Parameters on Three-Phase Short Circuit and Demagnetization in Surface-Mounted PM Machines

Demagnetization is one of the major concerns in PM machines, especially in surface-mounted PM (SPM) machines. Three-phase short circuit (3PSC) is one of critical faults that may cause demagnetization and thus 3PSC current should be reduced. Since key factors influencing 3PSC current, such as PM flux linkage, resistance and inductance, heavily depend on dimensional parameters, 3PSC current can be reduced by properly selecting them. In addition, dimensional parameters also influence armature field paths and thus demagnetization can be further mitigated by proper design of dimensional parameters. This article first investigates the influence of dimensional parameters on 3PSC current and demagnetization in an internal rotor concentrated-winding SPM machine. The results show that although larger airgap length reduces 3PSC current, demagnetization deteriorates. Moreover, 3PSC current increases and demagnetization aggravates when pole-arc to pole-pitch ratio, slot opening width and rotor yoke height increase or tooth tip height decreases. 3PSC current first increases and then decreases when split ratio and tooth width increase, which makes demagnetization first get worse and then eased. Then the influence of PM temperature, rotor speed, external rotor and winding configuration is investigated. Finally, experiments are implemented to validate the theoretical analysis.