Sensorless control of five-phase brushless DC motors

The present paper shows a rotor position estimation technique for a five-phase permanent magnet synchronous motor based on a back-EMF observer, focusing the attention on the design criteria that could be used to construct the sensorless strategy. Due to the polyphase structure of the machine this estimation method deals with a proper linear transformation which allows representing the five-phase motor through an equivalent two-phase model. After a short overview on the back-EMF model for the five-phase motor, the linear transformation and the observer-based estimation technique are presented. The analysis emphasizes on the choice of the observation dynamics through a proper design strategy of the related gain matrix and on some robustness criteria useful to enhance the sensorless strategy. Simulation and experimental results showing the response of the observer during transient and steady-state operation are presented.