General nonlinear mapping function between fluxlinkage/ torque to stator currents.
I. INTRODUCTION NTERIOR permanent magnet (IPM) machines are increasing being favored as the machine of choice for electric vehicle application due to their high power density, robustness, large constant power speed range and overall high efficiency [1]- [6]. However, due to presence of magnets in the rotor, electrical faults must be quickly detected and mitigating controls initiated to prevent catastrophic failure of the machine. Such a functionality commonly known as "limphome" mode [7] is essential for providing high degree of availability, and reliability demanded in safety critical application such as electric vehicles. In order to develop sensitive fault detection algorithms and fault tolerant control strategies, an accurate transient model of the machine under fault condition is indispensable [8]-[10] at development stage in order to save time and resources spent on experimental testing. This is because many faults such as inter-turn shortcircuit may cause benign changes in terminal voltages and currents. Consequently, it is difficult to detect them in an electrically noisy environment. Inaccurate representation of fault behaviors may lead to a detection algorithm working well in simulations, but not effective in real testing.Several surveys on reliability of industrial motors conducted by Electric Power Research Institute EPRI [11] and IEEE [12]- [15] concluded that stator winding failures accounts for about 21-37% of faults in electrical machines. One of the leading causes of winding failure are inter-turn short-circuit failures which are especially critical, since it leads to a large circulating current in the faulted turns [16]. This gives rise a local hot spot which can cause further insulation failures and ultimately leading to a complete failure of the winding as a phase-ground or phase-to-phase fault [17]. The large circulating current in the faulted turns can also produce irreversible demagnetization of the magnets [18].The modeling of inter-turn short-circuit fault in IPM was treated in [19] [35] assumes that the machine operates in linear region under healthy condition. However, this assumption is not applicable to IPM machines with high level of magnetic saturation [32]. The aim of this paper is to establish an accurate and computationally efficient model of IPM machines under stator turn fault. This is achieved by extracting flux linkage map of the machine under turn fault conditions using offline static FE analysis and combining it with voltage equations of the machine. The method is not limited to IPM machines and the same technique can be used for modeling stator turn faults in passive rotor systems including surface PM machines, switched reluctance machines, switched flux machines and, separately excited machines, such as wound field synchronous machines. This approach enables the full representation of spatial harmonics and magnetic saturation under inter-turn fault and all load conditions and therefore i...