Comparison of torque estimators for PMSM

One of the disadvantages of permanent magnet synchronous motors (PMSM) is the output torque ripples which degrade the performance of the system. Actual torque feedback to the system reduces output torque ripple but increases costs through the use of a torque transducer. Thus, a torque estimator which can provide accurate instantaneous torque feedback to the system will be highly desirable. However, there is no previous work comparing the different methods in estimating torque for a PMSM. This paper will compare four torque estimators using MATLAB/Simulinktrade to test how well the estimated torques are when compared to the actual output torque. The four criteria used for comparing the performance of the torque estimators are accuracy, robustness, complexity and cost. Depending on the type of operations, the torque estimators have different performance. From the simulations, it is found that if high accuracy and robustness is needed, model reference adaptive system (MRAS) and sliding mode observation (SMO) may be the best choices. However, if low cost and low complexity is desired, general torque equation (GTE) and flux estimation with compensation scheme (FCS) should be chosen.