Demagnetization in permanent magnet synchronous motor (PMSM), caused by high temperature or inverse magnetic field, may increase loss and torque ripple, and even degrade the system stability in severe cases. On‐line detection can identify the incipient demagnetization of permanent magnets (PMs), as well as providing reference for subsequent fault‐tolerant control, so as to avoid further demagnetization. Therefore, an on‐line demagnetization detection method is proposed in this paper by using flux observer. First, an observer is established in the three‐phase stationary reference frame by taking the stator currents and the amplitudes of the fundamental and harmonic components of flux as state variables. Then, three demagnetization indexes are presented to evaluate the properties of PMs based on the observed flux information. The proposed method can directly track the amplitude of harmonic flux and evaluate the severity of the demagnetization more comprehensively. Simulation and experimental results demonstrate the effectiveness of the proposed method.
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