A sensorless commutation strategy for a brushless DC motor drive system based on detection of back electromagnetic force

In this paper a sensorless commutation strategy for a brushless dc motor without using any analog filters or integrators is proposed. This technique is based on the estimation of the back-EMF of the non-conducting phase using the three terminal voltages of the machine with respect to the half of the DC voltage. A constant phase shift of 30° is achieved, independently from the operating point of the motor. The performance of the system using this strategy is assessed by simulation in MATLAB/ SIMULINK software. Two operating scenarios are investigated at different rotor speeds in order to prove wide operation range of the proposed strategy.