Mitigation of cross-saturation effects in resonance-based sensorless switched reluctance drives

The stator and rotor yoke in a switched reluctance motor form magnetic circuit parts that are typically shared by different phases. If these parts saturate due to the excitation of one phase, this will lead to a change of the magnetic characteristics of all other phases sharing these parts. In several position-sensorless methods, cross-saturation leads to a load-dependent position estimation error. In this paper, the influence of cross-saturation on a resonance-based position estimation method is studied. The method extracts position information from electrical resonances triggered in an idle motor phase. A cross-saturation mitigation scheme is presented in order to reduce the commutation position error. The scheme uses only one additional parameter per phase which can be measured automatically during commissioning of the drive. Experimental results at low and medium speed show that the position estimation error remains smaller dan 2 mechanical degrees over the rated load range