An-Najah Staff

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.

A new method to estimate the rotor position of permanent magnet synchronous motor (PMSM) drives over a wide speed range, including zero frequency is introduced. The method measures the motor current derivative in response to the standard pulse width modulation (PWM) sequence to estimate rotor position. No additional signal injection or separate test vectors are required although modification is needed when narrow PWM voltage vectors occur. Three compensation techniques are proposed to improve the quality of the position estimation and reduce current distortion when narrow vectors are used for position estimation. Experimental results for sensorless speed and position control of a 4 kW PMSM verify the effectiveness of the proposed techniques