Velocity observer for PMSM without rotational transducer

In this paper, a velocity estimator is proposed for the purpose of improving the transient velocity control performance of a permanent magnet synchronous motor (PMSM) operating without a rotor position or velocity transducer. An observer is designed to estimate rotor velocity using the electro-mechanical parameters of the system, measured stator currents, and the estimated rotor angle, where the angle estimate is obtained from a separate observer. Special attention is given to very low speed operation where the rotor angle estimate may be inaccurate due to ill-conditioning of the rotor angle observer under those conditions. Experiments are used to examine the velocity control performance of the resulting sensorless PMSM drive and the robustness of the system to external disturbances and model uncertainty.