Saliency tracking based sensorless control of AC machines exploiting inverter switching transients

Control of ac machines at zero frequency usually requires the presence of a rotor speed sensor. Sensorless control is so far possible around zero frequency when exploiting inherent saliencies of the machine. Current techniques use injected high frequency signals or the machine's step response to extract and identify magnitude and position of inherent saliencies. In this paper, a new method is presented to determine the inherent asymmetries using only the information provided during the switching transients of the machine current. While known techniques need an injected high frequency voltage, specific switching patterns, or modifications in the PWM scheme to exploit the current reaction, the proposed method is able to extract the necessary information from the transient current signal that directly follows the steep voltage change of the switching transition. Thus, the standard PWM scheme can be applied without modifications. Measurement results are presented to show the influence of the saliencies on the switching transition current ripple.