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. Current distortion introduced using two-level convertersBoth the INFORM and FPE sensorless control methods track the rotor slotting saliency in an induction motor by deriving an estimate of the drive's incremental inductance. This is achieved by measuring the motor current derivatives (di/dt) in response to specific voltage vectors applied to the motor. The INFORM [4] method applies these test vectors as specific pulses during the zero or null vectors of the normal PWM waveform. As these test vectors introduce a voltage
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