A novel technique for sensorless control of high power induction motors using multilevel converters

This paper introduces a new scheme to track the rotor slotting saliency in induction motors by using the measurement of current derivatives in response to test vectors imposed during null switching vectors of a standard PWM scheme by using 3 H-bridges connected in series with a 2-Level inverter. The scheme aims to reduce the current distortion usually introduced by applying the sensorless control strategies in 2-Level inverters. The H-Bridges can generate low voltage test vectors which can be used to track the rotor slotting saliency and the same time reduce the distortion in the current directly, as well as shortening the minimum pulse width (t_min) which adds a further improvement to current distortion without compromising the quality of the sensorless performance of the system. Moreover, the new technique can work in a wide speed range and its implementation requires only the minimum of control modifications to the operation of the multilevel inverter as 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. Also some automotive drives have recently been proposed which use the same specific topology as used in this work.