Back-EMF Based Sensorless Control of IPMSM with Enhanced Torque Accuracy Against Parameter Variation

In this paper, a method to compensate parameter variation of IPMSM for accurate torque control in sensorless control mode is proposed. First, a full-order observer for flux estimation of IPMSM is described, and how the inductance error affects the error of back-EMF estimation is analyzed. Next, the condition in which the real torque and the calculated torque based on current-model are the same is derived. And, an inductance compensator for achieving the condition is designed. The compensator can identify the variation of d-q inductance according to temperature and manufacturing tolerance. In addition, the back-EMF constant, which is the flux linkage of the permanent magnets, can be indirectly compensated through the adaptation of d-q inductance. Simulation and experimental results verify that the torque can be controlled within the accuracy less than 2% of the rated torque in various operating conditions despite ±20% of inductances variation and ±10% of back-EMF constant variation.