An Effective Ellipse Fitting Technique of the Current Response Locus to Rotating HF Voltage Injection in IPMSM for Sensorless Rotor Position Estimation

Sensorless control schemes are object of great interest in the synchronous motor drives field. They permit to avoid the use of position sensors in the system, allowing several benefits. In this paper a sensorless control scheme is proposed for low speed or standstill operation of a synchronous motor drive, characterized by a rotor anisotropy. The method is based on a high frequency voltage injection in the stator motor windings. High frequency current response to this injection is obtained from the measured currents thanks to a high pass filter. These filtered currents describe an ellipse trajectory, that is deeply analysed considering all its components. In particular, ellipse major semi-axis tilt is related to the rotor position. A recursive least squares estimator is proposed for the ellipse equation coefficients identification. After some manipulations, the rotor position is extrapolated from these information.