Sensorless control of high power induction motors using multilevel converters

This paper introduces a new scheme to track the rotor position of an induction motor, which reduces distortion introduced into the motor current by sensorless control techniques. The scheme uses the measurement of current derivatives in response to test vectors imposed during the null switching vectors of a standard PWM scheme. The test vectors are derived from H-Bridges connected in series with the main converter. These H-Bridges generate a lower voltage test vectors which will reduce the distortion in the motor current directly without compromising the quality of the sensorless performance of the system. The proposed application of this sensorless technique is to high power multilevel converters which use a combination of series connected GTO and IGBT based H bridges to achieve a reasonable quality medium voltage waveform for motor drives, although there are now similar topologies proposed for automotive drives. The implementation of this sensorless technique in such applications requires modification to he control software only.