Influence of stator configuration on high frequency signal injection based permanent magnet temperature estimation methods in PMSMs

The performance and life expectance of Permanent Magnet Synchronous Machines (PMSMs) is strongly affected by the PM temperature. An increase of the PM temperature reduces the PM strength and consequently the machine torque production capability. Also there is a risk of irreversible demagnetization if PM temperature is too high. Directly measurement of the PM temperature is not easy, PM temperature estimation methods have therefor been widely investigated during the last decade. PM temperature estimation methods can be divided into thermal models, BEMF methods and methods based on the injection of some type of test signal in the stator terminals of the machine. Thermal models require previous knowledge of the machine geometry, materials and cooling system. BEMF and high frequency signal injection methods do not require previous knowledge of the machine geometry or cooling system. However, BEMF methods require that the machine is rotating. High frequency signal injection methods can be used at any speed, including standstill. However, there is a number of issues that can affect to the accuracy of these methods, including stator and rotor designs, machine assembling tolerances and rotor lamination grain orientation. This paper analyzes the sensitivity of high frequency signal based temperature estimation methods to the stator design.1