Model Free Predictive Control Method To Suppress Commutation Torque Ripple For Brushless DC Motor

Brushless DC(BLDC) motors are widely being used in industrial control and daily life due to their high efficiency, low noise, long life and high reliability. But the torque ripple generated when they work in the commutation process seriously affects their application in the precision servo system. In order to suppress the commutation torque ripple of brushless DC motors, this dissertation mainly studied in the pulse width modulation and current commutation.The characteristics of brushless DC motor system are analyzed, and the commutation torque ripple caused by different modulation modes are analyzed, then the effects of different control modes of power switch are compared. In this paper, the current rate of the three-phase windings in the commutation process is analyzed. It is concluded that the torque changes under different speed are also different. During the commutation, the electromagnetic torque is proportional to the non-commutation phase current, so the control of non-commutation phase current stability can suppress the commutation torque ripple.This paper presents model free predictive control method to suppress commutation torque ripple of BLDCM, combining with universal model and predictive control. Borrowing the universal model, this method takes the non-commutation phase current as input of the controller and the predicted current of next time as the output. In this paper, the expression of the universal model of brushless DC motor control system is derived and the model is used as the predictive model to predict the non-commutation phase current. And then the non-commutation phase current keeps constant by selecting the optimal switch state through the value function, and ultimately the commutation torque ripple is suppressed.The non-commutation phase reference current value is used in the process of model free predictive control, but the calculation of the reference current value is based on ideal trapezoidal back electromotive force(EMF) wave. Pointing at the non ideal back EMF, this paper proposes reference current optimization strategy to compensate the torque error in the control process to suppress the commutation torque ripple.The simulation model is established in Matlab/Simulink and experiments are carried out in the brushless DC motor experimental system which takes the DSP TMS320F28335 as the core controller. The feasibility and effectiveness of model free predictive control method to suppress the commutation torque ripple are verified through simulation and experiment. The results show that the proposed method can effectively suppress commutation torque ripple of BLDCM at low and high speed under the rated speed condition. The parameters of electric machine are not necessary in the control process, and the algorithm is simple and easy to realize.