Airgap Flux Search Coil-Based Estimation of Permanent Magnet Temperature for Thermal Protection of PMSMs

Airgap flux monitoring, commonly used in wound field synchronous generators, has recently received a lot of attention for detecting faults in permanent magnet synchronous motors (PMSM), since a low-cost airgap search coil can provide reliable detection of motor faults. In this article, the feasibility of using the airgap search coil for estimating the temperature of the PM,
T_PM
, for thermal protection is evaluated for the first time. The 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 negative impact of high frequency signal injection can limit their practical use. The new
T_PM
estimation method based on the airgap search coil voltage measurement proposed in this article does not require compensation for resistance variation or inverter non-linearity, or injection of high-frequency signals. In addition, it can provide detection of rotor faults, and 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 with the proposed method.