Intermodulation-based Sensorless Control of Induction Machines Using Rotating Hf-Signal Injection Considering Inverter Nonlinearities

Abstract

Sensorless control offers many advantages for the operation of electrical machines. Being able to operate the machine via field-oriented control without relying on the encoder greatly increases the reliability of the drive. In the low to zero speed region, saliency based control strategies are well suited. For several standard industrial motor designs, induction machine can exhibit multiple inherent spatial saliencies linked to position. For such multi-salient induction machines, the intermodulation saliency has shown good characteristics for sensorless control. Transient excitation can be used to extract said intermodulation saliency. However, it requires intervention in the current controller pulse-width-modulation sequence and greatly oversampled current. Alternatively, rotating high frequency injection can be used to extract the intermodulation saliency, which offers simpler implementation possibilities. The rotating voltage space vector can simply be superimposed onto the current controller output. Additionally the current does not need to be oversampled. However, since the resulting high frequency current is not controlled, it is distorted by the inverter nonlinearities. Compensating the unwanted saliencies and inverter-related harmonics, the intermodulation saliency will be used in this paper to extract the rotor positon of multi-salient induction motors from the high frequency current. The experimental position estimation quality is tested at different stationary loads and transient load steps. Applicability is verified on a traction machine designed for railway application.