Direct torque control of Brushless DC motor without flux linkage observation

The direct torque control method of Brushless DC motor (BLDC) is different from that of permanent magnet synchronous motor for its turn-off phase and non-sinusoidal back electromotive force. To overcome these problems, a novel direct torque control method is presented in this paper. In order to control the torque effectively and directly, the torque is calculated according to the back electromotive force and three phase current in this paper. And the calculation of back electromotive force is achieved by making use of the shape function. The principle of shape function is that the amplitude of the back electromotive force is proportional to the rotor speed. It is the function of motor speed and rotor position. By utilizing the shape function and stator current, the calculation of torque is achieved easily. According to the torque error between the given torque and actual torque, the best voltage vector is selected and the dynamic performance of BLDC motor direct torque control system is guaranteed. The analysis is verified by the simulation and experiment results.