Using switching transients to exploit sensorless control information for electric machines

Model-based control strategies of induction machines usually require a rotor speed sensor if operated around zero fundamental electrical frequency. Sensorless control based on the exploitation of the inherent saliencies can be applied in this operating range. To identify magnitude and position of these saliencies injected high frequency signals or the current reaction on transient voltage steps can be used. Current techniques need to apply specific switching pattern or modify the PWM (pulse width modulation) scheme to exploit the machine response. This results in a higher torque and current ripple as well as additional acoustic noise emission. The proposed new measurement overcomes these disadvantages by using oversampling techniques to extract the wanted information from the switching transients in the current signal. Therefore it is possible to apply standard PWM without modification to ensure accurate flux or rotor position estimation. Measurement results will be shown and compared for the standard and the proposed approach.