Position-sensorless control method for permanent magnet synchronous motor using speed observer and induced voltage caused by magnetic saturation

This study presents a novel estimation method for the position-sensorless control of a permanent magnet synchronous motor at low speed range using an instantaneous speed observer and induced voltage caused by magnetic saturation (IVMS). The estimated position, which is based on an approximate linear equation of the IVMS, changes depending on the rotor position calculated by the least-square method in certain intervals and is used as the input of speed observer instead of real position information. The IVMS-based position detection methods can be applied to non-salient and closed-shelf motors at low speed range, where back electromotive force-based methods are difficult to apply. Additionally, the current waveform is well-controlled in the proposed method, and remains sinusoidal when the IVMS is not measured; thus, it improves energy efficiency and reduces torque ripple from conventional methods. The position estimation method and its experimental results are presented in this paper.