Rotor magnet demagnetisation diagnosis in asymmetrical six‐phase surface‐mounted AC PMSM drives

Abstract

Multiphase permanent‐magnet synchronous machines (PMSMs) are receiving more and more interest in safety‐critical modern industries owing to their higher reliability when compared with conventional three‐phase PMSMs. Rotor magnets are critical components, which, in case of fault, directly affect the performance of the PMSMs. Thus, monitoring the rotor magnets status is essential to ensure both high level of efficiency and service continuity. The present study focuses on the investigation of a new approach for the detection of rotor magnet demagnetisation in a vector‐controlled asymmetrical six‐phase surface‐mounted AC PMSM. The main contribution of the proposed technique is the assessment of a rotor demagnetisation fault index derived from the fifth and seventh harmonics of the stator voltage space vector evaluated in the α 5–β 5 ‐plane, and already available in the control system platform. The performance of the proposed approach is evaluated using finite element analysis and numerical simulations, both validated by experimental tests.

A Comprehensive Survey on Fault Tolerance in Multiphase AC Drives, Part 1: General Overview Considering Multiple Fault Types

“…On the other hand, there are numerous faults that do not solely affect some of the stator phases, but all of them to similar extent. This occurs, e.g., in case of shortage [138,466,467], excess [131,132] or sensor failure [58] of dc-link voltage v dc (for single-dc-link drive), magnet demagnetization [75], as well as mechanical (e.g., eccentricity or damaged bearings/bars) [79,81,82,84,85], speed/position-sensor [182,199], or machine cooling-system failures (increasing temperature) [60,70,71,468], among others. The phase redundancy of multiphase machines, in principle, does not seem to offer inherent tolerance against these kinds of faults.…”

“…This problem can arise as a consequence of various reasons. For instance, it can be caused by manufacturing defects, corrosion or mechanical stress (e.g., cracked magnets) [74,75,78,583]. Nonetheless, one of the most common origins of demagnetization is excessive temperature [72,74,75,78,129,177,267,583], e.g., due to a failure of the machine cooling system or to large current.…”

“…For instance, it can be caused by manufacturing defects, corrosion or mechanical stress (e.g., cracked magnets) [74,75,78,583]. Nonetheless, one of the most common origins of demagnetization is excessive temperature [72,74,75,78,129,177,267,583], e.g., due to a failure of the machine cooling system or to large current. The latter may be produced, e.g., by stator SCs [75,78,129,176,177,267], converter SCs [75,78,583], heavy load [129], or position-sensor faults [176,177].…”

“…Nonetheless, one of the most common origins of demagnetization is excessive temperature [72,74,75,78,129,177,267,583], e.g., due to a failure of the machine cooling system or to large current. The latter may be produced, e.g., by stator SCs [75,78,129,176,177,267], converter SCs [75,78,583], heavy load [129], or position-sensor faults [176,177]. Magnet demagnetization is often alternatively produced by intense magnetic field induced by high-current along the negative d 1 -axis direction [74,78,129,176,177,267,583].…”

“…Detecting irreversible demagnetization and its severity is useful for, e.g., assessing the amount of performance degradation associated with it, the urgency for replacing the faulty machine, and the maximum torque that can be set without causing overcurrent (which would worsen the demagnetization) [591]. In addition, monitoring the status of the magnet field is also helpful for preventing that reversible demagnetization evolves into irreversible [75]. As depicted in Figure 39, the diagnosis of demagnetization may be performed differently depending on whether it occurs locally or uniformly.…”