Influence of Healthy Winding Group Current on Three-Phase Short-Circuit and Demagnetization in Dual Three-Phase Surface-Mounted PM Machines

In dual three-phase surface-mounted permanent magnet (PM) machines, three-phase short circuit (3PSC) fault is usually assumed to happen in only one winding group whilst the remaining one can be normally supplied. This article investigates the influence of healthy winding group (HWG) current on 3PSC of faulty winding group (FWG) and the resulting demagnetization. Firstly, the article develops the analytical model of 3PSC current component caused by HWG current. Based on this, the influence of HWG current is analyzed. It is found that, for symmetrical winding configurations, the d- and q-axis peak 3PSC current can be reduced to their minimum values when HWG current angles are about 90 and 135 electrical degrees, respectively. In addition, the suppression is more effective when HWG current amplitude increases. However, for asymmetric winding configurations, the suppression effect heavily depends on 3PSC start rotor position. The optimal HWG current angles are given for different start rotor positions, which maximumly reduces the d-axis peak current and demagnetization. Then, this article investigates the influence of forcing HWG into 3PSC on peak short-circuit current. It is found that an additional inductance component is added in FWG when forcing HWG into 3PSC, which reduces the peak current. However, since 3PSC current in HWG can also lead to demagnetization, the overall demagnetization level can be mitigated only at relatively low PM temperatures. Finally, experiments are conducted to validate the theoretical analysis.