Full speed range permanent magnet synchronous motor control without mechanical sensors

This study presents a control method for permanent magnet (PM) motors based on a combination of a non-linear full-order observer and a signal injection scheme. Stable mechanical-sensorless operating range down to zero speed at full load is obtained using only voltage and current sensors. The signal injection scheme uses the asymmetry of the motor's d and q-axis inductances to estimate rotor position and speed. Such asymmetry is also taken into account in the motor model used to construct the observer to reduce current estimation error. The performance of the proposed scheme is validated through experimental results.