Improved method for higher dynamics in sensorless position detection

Abstract

Numerous methods have been published for sensorless detection of the rotor position in PM synchronous motors (PMSM) by evaluating the magnetic anisotropy. In this paper, the one based on the injection of an alternating voltage carrier is considered. It is able to detect the anisotropy, and by its means the rotorpsilas position, without any additional hardware or modifications on the samplings times. It will be shown that the observerpsilas dynamics is bounded by the carrier frequency. The carrier is usually sinusoidal and with a frequency of about 1/4 of the switching frequency or lower. As a measure to improve the dynamics of the position observation, a square wave carrier with the highest possible frequency, namely the switching frequency, will be used. In addition, the carrier response will be decoupled from the controlled q-current in order to avoid the usual bandpass filter. This filter would introduce a significant delay in the observer loop. The frequency increase, together with the removal of the filter allows a faster time response in the position estimation. Experimental results showing the improvements in the estimationpsilas dynamics are presented.