Robust current control for brushless DC motors

The winding current exciting responses of brushless DC motors significantly affect their torque generating characteristics and hence the whole drive control performance. To obtain a quick and accurate current command tracking response, the application of control strategies for compensating the effects of key parameter variations is necessary. Robust control for achieving improved current response is studied. First, the model parameters for performing the current control loop design are estimated. Then a novel current control scheme is proposed, which consists of a feedback controller, a command feedforward controller and a robust disturbance cancellation feedforward controller. The former two controllers are designed to fulfil the desired current control characteristics at nominal case, and the robust controller is employed to reduce the effects of back electromotive force and parameter variations. The theoretic basis and design of the proposed control scheme are presented in detail. Through applying the designed current controller, the winding current response is speeded up and thus the motor drawn line current is decreased owing to the improved torque generating characteristics. The effectiveness of the proposed robust current control approach is demonstrated by simulation and measured results.