Predicted and measured errors in estimating rotor position by signal injection for salient-pole PM synchronous motors

The paper deals with the sensorless control of salient-pole Permanent Magnet (PM) synchronous motor drives, using a high frequency injected voltage for estimating the electrical angular position of the rotor. A high frequency speed-dependent ellipse rotating voltage vector is injected to the motor. It generates a high frequency current vector in the estimated synchronous reference frame, that contains information on actual rotor position. This type of estimation technique exploits the anisotropy of the rotor and gives an estimation that is not affected by rotor speed. A recent aspect of the topic intensively investigated is the behaviour of different rotor geometries when subjected to high frequency rotor position estimations and, consequently, the design of sensorless oriented configurations. The reasons of these studies arise from the iron saturation which occurs in the rotor and that modifies and can even cancel rotor saliency and introduces a cross coupling (cross-saturation) between d- and q-axis. This paper experiments the behaviour of two of the principal sensorless oriented rotor configurations and compare the experimental results with those predicted by the finite element simulations carried out during the motor design, in order to validate prediction tools and find out new design hints.