Torque ripple estimation and minimisation independent of sensor type

Abstract

Torque ripple exists at the output of permanent magnet synchronous motors (PMSMs) as a result of current error, non-sinusoidal back-EMF and cogging torque. Since part of the cogging torque component is based on manufacturing error, motor design may not eliminate all torque ripple. One possible method for reducing torque ripple is by injecting the inverse of a torque ripple estimate to the current controller. Torque estimators that include cogging torque rely on feedback from different sensors such as vibration sensors and accelerometers, microphones, speed and torque sensors. This paper outlines a control method that can utilize any sensor with a linear transfer function between the torque and the sensor input. The method determines an estimate of the torque ripple for a number of harmonics simultaneously, as well as the transfer function between the torque and the sensor. Experimental results show different sensor types provide similar estimates of the torque with less than 2% variation in magnitude for the sensor types used. Experimental results show that regardless of which sensor type is used, critical torque harmonics are reduced by at least a factor of 3.