Influence of different inverter control and test generation schemes on sensorless control of AC machines

High dynamic AC motor drives usually need a sensor at the motor shaft to determine the flux position of the machine in the whole frequency range. Omitting this sensor would not only reduce costs but also increase the reliability of the drive. Though different approaches for sensorless control have been published in the past years there is till no new method which is industrially applied on standard induction machines. To work even at zero flux frequency the sensorless control scheme has to rely on side effects in the machine which are not covered by considering only the fundamental wave. One of these side effects is spatial saliencies which can be detected by evaluating the response of the machine to special excitation functions or exciting pulses impressed by the inverter. In this paper the influence of different space phasor modulation schemes as well as different methods to impress exciting pulses on the INFORM flux detection method is investigated and measurement results are presented. The measurements were made with an induction machine however the results are also applicable for example to permanent magnet synchronous machines. As the response of the machine on the transient excitation depends on the stationary and transient magnetic point of operation, the inverter control scheme has an important influence on the performance of the sensorless control. To compare the different modulation and excitation schemes, a comparison is made reference to the obtained current ripple and distortion of the sensorless control signal.