PMSM magnetization state estimation based on stator-reflected PM resistance using high frequency signal injection

Permanent magnet (PM) magnetization state estimation in Permanent Magnet Synchronous Machines (PMSM) is of great importance for torque control and monitoring purposes. The magnetization state of a PMSM can change due to several reasons, injection of stator current (d or q-axis) and variation of magnet temperature being the primary reasons. PM magnetization state estimation is not easy once the machine is assembled. Methods based on the back-EMF (BEMF) can be used, but they require that the machine is rotating. This paper analyzes the use of high frequency signal injection for PM magnetization state estimation in PMSMs. The magnetization state of the PMs in PMSMs affects the stator-reflected PM high frequency resistance. The stator-reflected PM high frequency resistance can be estimated by injecting a high frequency voltage/current using the inverter. The high frequency signal is superposed on the fundamental excitation used to produce torque, meaning that the method can operate at any speed, including zero speed, and without interfering with the normal operation of the machine.¹