Brushless Dc Motor Direct Torque Control

Permanent magnet brushless DC motors(BLDCM)have been more and more widely used in industry applications. However, torque tipple is the main drawback of BLDCM, which makes the application of BLDCM in the high accuracy system impossible. So it is desirable to minimize torque ripple in a brushless dc drive. The direct torque control(DTC) has good performance and it has been successfully applied on induction motor and permanent magnet synchronous motor. This paper describes the application of DTC to brushless dc drives and highlights the following two improved approaches for reducing torque ripple in its implementation.To reduce the commutation torque ripple, which occurs in a conventional BLDC machine with two-phase 120°elec. conduction, a hybrid two-and three-phase switching mode and an improved voltage-vector-selection table are employed, which make use of three-phase switching mode during the commutation periods. And according to the error between the commanded torque and the estimated torque, it adaptively adjusts the conduction duration of the three-phase switching mode instead of precise calculation.To reduce the torque ripple during non-commutation period, a fuzzy controller based on the scheme of fixed frequency and adjustable pulse width is designed. Considering both the torque error and error variance ratio, the controller adaptively predicts the duty ratio between the action time of effective voltage vector and the controlling period.What's more, a SIMULINK-based simulation system and a TMS320F2812-DSP-based experimental platform were developed, then Simulation and experiments were done. The results show that the improved DTC method maintains the advantage of rapid dynamic response of conventional DTC and effectively reduces the torque ripple both in commutation and non-commutation periods.