Permanent magnet temperature estimation in PM synchronous motors using low cost hall effect sensors

Knowledge of the permanent magnet (PM) temperature in PM synchronous machines (PMSMs) is of great importance both for control and monitoring purposes. Increase in PM temperature during motor operation can degrade the magnetic flux strength and consequently the machine's torque production capability, also can cause irreversible demagnetization of the PM. Direct measurement of the PM temperature is not viable in practice, due to both cost and reliability issues. Indirect PM temperature estimation methods recently studied can require knowledge of thermal or electrical model parameters or can have undesired effects on motor operation. In this paper, the feasibility of using low cost hall-effect sensors for PM temperature estimation is investigated. Hall sensors are present for detecting the initial position of the rotor in majority of PMSM applications for which incremental encoders are used for control. The proposed method can therefore be implemented with low or no additional cost. Experimental results on two IPMSMs show that the method is capable of providing non-invasive estimation of the PM temperature without a priori motor parameter information for monitoring and protection against excessive increase in temperature.¹