The Research On Pulsating Torque Reduction For PM Brushless DC Motor

The performance of permanent magnet brushless motors is improving with the development of Power Electronic Technology and permanent magnet material. It has been widely used in the motion control applications, such as weapon systems, aircraft and spacecrafts, elevator towage and AC servo drives. However, the main disadvantage of permanent magnet brushless motors is its pulsating torque. Torque smoothness is an essential requirement in the motion control applications. So the compensation of pulsating torque is very important.The pulsating torque of permanent magnet brushless motors composed of torque triple and cogging torque was theoretically analyzed in this paper. The reasons of torque ripple production and the harmonious waves in torque ripple are studied based on the mathematic model of permanent magnet synchronous motor, which is important to reduce the torque.For the connatural question of permanent motors, we analyzed the mechanism of cogging torque. In this paper, a compensation method based on the i_d=0 vector control is presented to reduce the influence of cogging torque on the motors through the harmonic current injection. For this method, one compensation current is added to the q axis current to compensate the cogging torque. Simulation and experiment results show that the presented method is effective to compensate the cogging torque.As the temperature and magnetic path saturation of motor increase, the flux link will be change. For this problem, an adaptive controller is described. The rotor flux is estimated by adaptive control system in the d-q frame. As a feedback the estimated flux is used to actively changing the current waveforms to generate smooth output torque. The Simulation results show significant reduction of torque ripple.