Comparative Analysis of BEMF and Pulsating High-Frequency Current Injection Methods for PM Temperature Estimation in PMSMs

Permanent magnet synchronous machines performance is highly dependent on the permanent magnets (PMs) temperature. However, PM temperature measurement is not easy and is not normally implemented in standard machines. Alternatively, PM temperature can be estimated. PM temperature estimation methods can be divided into three major groups: thermal model-based methods, BEMF-based methods, and methods based on the injection of some form of high-frequency signal into the stator terminals of the machine. One concern for thermal model-based methods is that the model often needs to be adjusted for each machine design and application, knowledge of the machine geometry, materials, and cooling system being, therefore, required. On the contrary, BEMF methods and methods based on high-frequency signal injection estimate the magnet temperature from measurable electrical variables, knowledge of the geometry or cooling system not being required. Though they use the same type of signals, BEMF and high-frequency signal injection methods present relevant differences. This paper realizes a comparative analysis of both methods. Physical principles, performance, and implementation will be addressed.