Effect of position sensor error on the performance of PMSM drives for low torque ripple applications

Accurate measurement of motor shaft position is crucial in the motor drive application where smooth torque performance and better controllability are needed. The error in position along with the non-linearities in the measured currents cause error in the measured q-axis and d-axis currents and applied voltage, thereby introduces ripple in the developed torque. This paper analyzes the effect of various factors including magnetic and mechanical on the accuracy of the position measurement. A detailed mitigation method is provided to correct the position sensor non-linearities to improve the drive performance. It also analyzes the effect of the erroneous position on the developed torque of a permanent magnet synchronous motor (PMSM). Analytical formulations along with a closed loop current controlled PMSM drive model are developed to study the effect of the various sensor errors. Experimental tests are done to support the theoretical analysis and quantify torque ripple contributed from sensor non-linearities.