Evaluation of the influence of design and operation of standard induction motors on sensorless control schemes utilising saliencies in the transient electrical behaviour

Abstract

Control of induction machines without mechanical sensor even at zero fundamental frequency is a very challenging task. Though there are already some sensorless control schemes which have been presented in literature, there is up to now, no method which is actually used in industrial drives. All these methods utilise side effects in the machine which are not covered by a fundamental wave model of the machine. It seems that the most promising approach for sensorless control is the evaluation of saturation induced saliencies. However these saliencies and also their evaluation methods strongly depend not only on the point of operation of the machine but also on some design parameters. To determine the influence of these parameters as well as of the measurement equipment, it is necessary not only to analyse these effects but also to realise a test stand especially designed for this task to verify the considerations. The sensorless control scheme investigated is called the INFORM method ('indirect flux detection by on-line reactance measurement') and uses a transient excitation of the machine with voltage pulses applied to the machine by the inverter. The response of this transient excitation is exploited to estimate a control signal. To give a further insight into the transient distribution of the flux in the machine, measurement coils at different spots are used and evaluated. Different testing methods are applied to extract the modulation and influence of the different saliencies present in a standard induction machine.