Magnet temperature estimation in surface PM machines using high frequency signal injection

This paper proposes a method to estimate the magnet temperature in surface PM machines (SPMSM) using high frequency carrier signal injection. The injection of a high frequency signal, superimposed on the fundamental excitation, allows the estimation of the stator transient impedance, which is a function of both the stator and rotor impedances. The temperature of the magnets is shown to have a significant weight on the overall stator transient impedance, from which it can be estimated. The high frequency carrier signal is injected intermittently in order to minimize potential adverse effects on the normal operation of the machine. The paper first explains the physics behind the magnet temperature dependence. Then the principles of the method as well as its practical implementation are discussed. Experimental verification of the method is provided.