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Investigation of permanent magnet flux linkage variation in PMSMs due to temperature rise and magnetic saturation

Accurate information of permanent magnet (PM) flux linkage is of significance to high-performance control and condition monitoring of permanent magnet synchronous machines (PMSMs). During machine operation, the PM flux linkage can vary due to temperature rise and saturation. Thus, this paper investigates how temperature rise and saturation influence the PM flux linkage under different operation conditions. Under no-load condition, the PM flux linkage is estimated from the back-EMF test. Under load condition, a speed harmonic based PM flux linkage estimation approach is proposed, in which the PM flux linkage is estimated from the speed harmonic without requiring machine parameters. Thus, the proposed estimation approach is not affected by the machine and drive nonlinearities and thus can guarantee the estimation performance. The proposed approach is applied for PM flux linkage estimation under various loads and temperatures to investigate the influence of temperature rise and saturation on the PM flux linkage. Experimental results demonstrate that the PM flux linkage under no-load is larger than that under load due to magnetic saturation, the PM flux linkage under load decreases as the saturation level increases, and the one under both load and no-load decreases linearly as the PM temperature increases.