Motor Temperature Monitoring Based on Impedance Estimation at PWM Frequencies

This paper proposes a noninvasive temperature measurement technique of indirect type, applicable in the permanent magnet synchronous motor (PMSM) drives. The motor temperature is required for protection and monitoring purposes, as well as for updating temperature-dependent control parameters. Direct measurement with dedicated sensors requires peripherals and cabling; hence, it is quite involved and often avoided. Temperature estimation based on test signal injection contributes to torque ripple and often relies on other motor parameters. A solution is proposed here, which makes the use of intrinsic pulse-width modulation excitation and does not use electrical or thermal parameters of the considered PMSM. The temperature of the stator winding is estimated from the motor input impedance Z_IN(ω) calculated over the range of frequencies starting at and going well beyond f_PWM. The paper includes analytical considerations, implementation details and experimental verification obtained with a 4.5-kW PMSM used in battery-supplied propulsion systems.