Sensorless control of induction motors using multi-level converters

This study describes a sensorless speed control scheme for induction motors supplied by a multi-level inverter. The scheme exploits the low DC link voltage used in some of the multi-level converter configurations which employ H-Bridges. The rotor position is tracked by measuring the rate of change of motor stator currents when low-voltage test vectors are applied using the H-Bridges. In this way, the motor current distortion introduced by the sensorless control scheme is reduced compared to that seen when using a two-level converter. The proposed approach could therefore be applied to high-power motor drives, and automotive drive systems. The study presents a theoretical derivation of the algorithm and experimental results which show the improvement in the motor current quality achieved using the new technique compared to sensorless techniques implemented on a two-level inverter.