Sensorless Vector Control for PM Brushless Motors with Nonsinusoidal Back-EMF

This paper presents a new approach for sensorless vector control of surface-mounted permanent magnet brushless motors with nonsinusoidal back electromotive force (EMF). This approach uses a new motor dynamic model expressed in a synchronous reference frame with back-EMF vectors. The back-EMFs required for the frame transformations and for the rotor speed estimation are estimated online from a reduced-order state observer. In addition, a hybrid orientation is performed using variable cutoff frequency filters to select the back-EMF harmonic components that compose the synchronous reference frame. Hence, harmonic currents can be effectively reduce at high speed decreasing iron losses. Moreover, it is shown that the electromagnetic torque under nonsinusoidal orientation is proportional to the q-axis stator current. As a result, the torque ripple can be easily minimized even with highly nonsinusoidal back-EMF. The good performance of the proposed approach for speed and current control is demonstrated by simulation and experimental results.