Hybrid orientation for sensorless vector control of nonsinusoidal back-EMF PMSM

Abstract

This paper presents an alternative approach for sensorless vector control of permanent magnet (PM) brushless motors with nonsinusoidal back electromotive force (EMF). The approach uses a new dynamic model for surface-mounted PM motors, which is expressed in a synchronous reference frame with orientation on back-EMF vectors. Thus, it is possible to demonstrate under this orientation frame that the electromagnetic torque is proportional to the quadrature stator current similar to the classical vector control. As a result, the torque ripple can be easily minimized even with highly nonsinusoidal back-EMF. In addition, a nonsinusoidal vector control scheme is proposed using an observer to estimate the back-EMFs which are required for the rotor speed estimation as well as for the frame transformations. In order to allow energy efficiency improvement, a hybrid orientation scheme using variable cutoff frequency filters is adopted to select desired back-EMF harmonic components that compose the synchronous reference frame. Consequently, harmonic currents can be reduced at high speed to decrease iron losses. The good performance of the proposed approach is verified by simulation and experimental results.