Disambiguation of Uniform Demagnetization Fault from Position Sensor Fault in FOC PMSM Applications

 Electrification of higher torque density applications in the transportation sector and robotics sector are primarily met with permanent magnet synchronous machines (PMSMs), attributing to their unique properties. However, wide operating temperatures, field weakening controls, and low-quality magnets, lead to uniform demagnetization of rotor magnets. Demagnetization in torque control applications reduce the effective output torque as the output torque is proportional to rotor flux level. Detection of such rotor demagnetization is essential and only second to few key faults from the system perspective. A simple and common approach to detect uniform demagnetization in a sensored-FOC PMSM drive system in torque control mode is discussed in this paper with experimental results emulating uniform demagnetization effect. The false positive nature in the proposed algorithm under a position sensor offset error is discussed, followed by a disambiguation strategy, which are primary contributions of this paper. Analysis, simulation and experimental results are presented to validate the proposed disambiguation strategy.