Low speed sensorless control of an induction motor fed by multilevel converter to reduce current distortion

The paper introduces a new scheme to track the rotor position of an induction motor. The scheme uses the measurement of current derivatives during null switching vectors of a standard PWM scheme and reduces the minimum pulse widths required to allow high frequency switching oscillations to die down. The motor current distortion is therefore also reduced. The method uses H-Bridges connected in series with the main converter. This configuration has the same characteristics as the multilevel converters proposed for high power induction motor drives. The H-Bridges can be used to produce low voltage test vectors during the null vector which can provide a good rotor position estimation with very low additional current distortion. The paper will present experimental results which show the potential capability for sensorless speed control.