Airgap Flux-based Estimation of Permanent Magnet Temperature for Thermal Protection of PMSMs

Airgap flux monitoring has recently received a lot of attention as a low cost means of providing reliable fault detection for permanent magnet synchronous motors (PMSM). In this paper, the feasibility of using an airgap search coil for estimating the temperature of the PM, T
PM
, for thermal protection is evaluated. Thermal and electrical model- or signal injection-based methods proposed for T
PM
estimation can provide satisfactory estimates of the average T
PM
for thermal protection. However, the complexity in the compensation required for non-ideal effects and/or the invasiveness of high frequency signal injection can be limiting factors for implementation. A new method for T
PM
estimation based on the airgap search coil voltage measurement is proposed in this paper. The proposed method does not require compensation for inverter non-linearity or resistance variation, or injection of high-frequency signals. In addition, it can provide thermal protection based on the T
PM
estimate of the hottest PM since individual PMs can be monitored. Experimental results on a 2.2 kW IPMSM verify the claims and show that the existing methods can be simplified and enhanced with the proposed method.