Sensorless control of brushless DC motor using back EMF commutation

Abstract

Brushless dc motors require rotor position information for commutation and speed control. Resolvers, encoders or Hall effect devices are often used but they increase cost and size of the system. Therefore, a great deal of work on sensorless control of brushless dc motor has been carried out for a few years. This report describes the principles and implementation of a sensorless control system using the principle of Back Electromotive Force (back emf) Commutation. As the proposed control scheme uses an open loop procedure to start the motor, the open loop to closed loop transition has been investigated. The system allows a rehable control and reversal of the motor, even at low speed. The implementation of the control algorithm in a TMS320F240 DSP is described. The test results on a 20 V, 10000 rpm, two-poles motor have been found satisfactory when run with no load. The load tests, made by holding the shaft, showed that the motor sometimes stopped at low speed.</p