Sensorless control technique of PMSM based on MRAS observer with smooth transition

A sensorless speed control for Permanent Magnet Synchronous Machines (PMSM) is proposed in this paper. Based on the Electromotive Force (EMF), the Model Reference Adaptive System (MRAS) observer estimates the rotor speed and position. The use of the MRAS observer instead of the stator voltage model improves the dynamics, robustness and stability of the drive system. For validation, a field-oriented speed control is implemented on a microcontroller for a PMSM. A rim thruster impeller motor is used as PMSM. Due to the small values of the stator resistance and the stator inductances, the sensorless control of the rim thruster impeller motor is associated with some difficulties. External influences, such as connection cables or temperature, can change these very small parameters considerably. In the following, a test bench is set up to implement and test the control algorithms with the MRAS observer on a microcontroller. The stator voltage model is used as a reference model for estimating the rotor speed and position. The presented method provides an effective strategy for sensorless speed control of a PMSM. A specially designed angular sliding mode ensures a smooth transition to the field-oriented control (FOC) and prevents instabilities during switching from the controlled angle to the observer's estimated angle.