Analysis of a deeply saturated sensorless PMSynRel drive for an automotive application

This paper presents an method of mapping feasible region for a sensorless control PMSynRel drive using the resulting position error signal. Thanks to the rotor anisotropy, the rotor position can be detected at low speeds by means of injecting high frequency voltage, either a pulsating voltage vector in the estimated synchronous frame or a rotating vector in the stator frame, on top of the fundamental excitation. However, the resulting position error signal is degraded and distorted by magnetic saturation (including cross-saturation) and spatial inductance harmonics. Therefore, the feasible region is used to find the stable operating points. Instead of mapping the inductances, which is time consuming, position error signal is used to map the feasible sensorless control region. A prediction method of the maximum position estimation error is also presented by taking the spatial inductance harmonics into account. After that, some techniques are presented to compensate the cross-saturation and slot harmonic effects in order to improve the sensorless control quality. Additionally, it is shown how saturation in the rotor bridges affects the initial polarity detection required during startup.