Online PMSM Magnet Flux-Linkage Estimation for Rotor Magnet Condition Monitoring Using Measured Speed Harmonics

Rotor magnet flux linkage is critical to monitor the state of the permanent magnet in a permanent magnet synchronous machine (PMSM). This paper proposes a novel online magnet flux-linkage estimation approach by using measured speed harmonics. The proposed approach is based on the PMSM's mechanical equation, so it is not influenced by magnetic saturation, inverter nonlinearity, and changes in machine parameters. The interaction of magnet flux linkage and harmonic current can produce torque harmonic, and thus speed harmonic. Therefore, we explore the use of speed harmonic for magnet flux-linkage estimation. At first, the torque and speed harmonic models are proposed. Then, the mathematical relationship between magnet flux linkage and speed harmonic is developed. Based on this model, a novel magnet flux-linkage estimation approach is proposed, which can eliminate the influence of the cogging torque and spatial harmonics in magnet flux-linkage estimation. The proposed approach is validated on a PMSM drive system under different loads and speeds.