Brushless DC motor control without mechanical sensors

This paper describes two methods of estimating rotor position and speed of a brushless DC motor. The eradication of such sensors has been the subject of many publications. The rotor position as well as the machine speed are estimated strictly and used for the sensorless control of PMSM. The first method, based on the solution of the electrical equations is hard to implement (for low power machine) because of the derivative on the currents. In this study, with the help of state observer technique (second method), the proposed method to estimate the rotor position and speed was verified by experimental results of a 500 W PMSM. The paper shows implementation of the observer using a TMS320C31 digital signal processor system. Experimental results, demonstrating a good starting stability, a robustness, a steady state and transient performances for the proposed sensorless scheme are presented.