Abstract-Most permanent magnet machines are driven by inverters with pulse width modulation (PWM) voltages. The currents contain high frequency (HF) components which are inversely proportional to machine inductance. The HF PWM ripple currents can be used to detect a turn fault that gives rise to changes in inductance. The features of these HF components in turn fault conditions are analyzed. A bandpass (BP) filter is designed to extract the selected sideband components, and their root-mean-square (RMS) values are measured. The RMS values in all phases are compared. It is shown that the RMS ripple current ratios between two adjacent phases provide a very good means of detecting turn fault with high signal-to-noise ratio. The detection method can identify the faulted phase, tolerate inherent imbalance of the machine, and is hardly affected by transient states. The method is assessed by simulations and experiments on a five-phase permanent magnet machine.
Index Terms-Permanent magnet (PM) machines, Pulse width modulation (PWM), high frequency (HF) components, root-mean-square (RMS) measurement, turn fault detection
I. INTRODUCTIONPermanent magnet (PM) machines are becoming increasingly attractive in a variety of drive applications, due to their high performance and high efficiency. However, in these applications such as electrical vehicles (EV) [1][2] and more electric aircrafts (MEA) [3], high reliability is of great importance. An unexpected fault or failure in PM machine drives may lead to very high repair or replacement cost, or even catastrophic failure.Turn-to-turn short circuit fault (also known as turn fault, or inter-turn fault) is one of the most severe faults [4] [5]. The main cause of inter-turn faults is winding insulation deterioration as described in [6], which results from combined mechanical, electrical and thermal stresses in the stator winding. The stresses may lead to an insulation break-down of the coil conductor, which may short out some of the turns. When an inter-turn fault occurs, excessively high current will circulate in the shorted turns and increase the winding temperature to a level where severe damage or even breakdown of the whole insulation occurs [7]. In some PM machines, the large short-circuit current can produce localized magnetic field intensity higher than the coercivity of the magnets, thereby demagnetizing the magnets irreversibly [8]. Also, a large percentage of the insulation failures starts from a turn-to-turn insulation problem and subsequently develop into more severe insulation faults, such as coil-to-coil short circuit, phase-to-phase short circuit, and phase-to-ground short circuit, all of which lead to substantial damage to the machine. Therefore a swift detection of inter-turn short fault during machine operation is essential to avoid subsequent damages, and reduce repair cost and drive outage time.In recent years, turn fault detection has been extensively studied, and various techniques and methods have been proposed. One of the most popular techniques is based on...
