Analysis of Saliency-Based Position Estimation for Permanent Magnet Machine with Saturation Reflected Non-Sinusoidal Inductance

This paper analyzes the saliency-based position estimation for the permanent magnet (PM) machine with non-sinusoidal inductance. Considering the saliency-based sensorless drive relying on the spatial information of machine inductance, an ideally sinusoidal inductance is assumed to estimate the rotor position. However in actual PM machines, non-sinusoidal inductances are typically resultant due to the stator slotting effect, rotor topology, and most importantly, the saturation caused by magnet flux and coil flux. In this paper, a systematic analysis of saliency-based position estimation errors caused by the non-sinusoidal inductance is proposed. It is shown that the saturation decreases d-q self-inductances while increases d-q mutual-inductances. In addition, secondary inductance harmonics increase as saturation increases. The saliency-based drive ultimately fails because of considerable position errors. This paper clearly defines the feasible drive operating area for highly saturated PM machines. An optimal current control strategy is developed to maintain the drive stability for full load operation. Finite element analysis (FEA) is used to simulate the inductance saturation at various load conditions. A 5kW interior PM (IPM) machine with highly non-sinusoidal inductance is analyzed.