Evaluation of lamination materials in zero-speed sensorless controlled induction machine drives

Control of induction machines without mechanical sensors has gained more and more interest in the past years. Different methods for sensorless control have been proposed in literature recently. The performance of methods, which are based on fundamental wave models of the machine deteriorate at low frequency. To guarantee a stable operation, even at zero fundamental electrical frequency, it is thus necessary to exploit parasitic effects of the machine, which are not visible in normal operation of the drive. All proposed zero-speed methods have in common, that they need an additional excitation of the machine in order to make parasitic saliencies visible. This additional excitation can be a high frequency current or voltage signal of some hundred Hz which is superposed to the fundamental wave, and which may be a rotating or pulsating signal. Another way of excitation can be realised by applying voltage test pulses to the terminals of the machine. These voltage pulses may be either separated from the fundamental wave PWM or they may be integrated into the current control scheme. All mentioned methods evaluate the high frequency current or voltage response of the machine in order to extract a flux- or rotor-position signal. It is thus important to consider the high frequency properties of the lamination sheet when designing a sensorless controlled drive. In this paper, a sensorless control method using voltage test pulses is applied to different induction machines, all with the same winding scheme and lamination design, but with different lamination materials. Thus the materials influence on the sensorless control is evaluated by comparing the different machines control signals. In addition, all machines are equipped with measurement coils at different spots of the machine which enable a comparison of the transient flux linkage change along the air gap of the machine.