The Research Of Discrete Current Control For BLDCM Based On No Beat Current Predictive Control

The structure and operation principle of the permanent magnet brushless dc motor is analyzed first in this paper. According to the facts that the torque ripple during the commutation is big and the positioning accuracy is not high, a kind of discrete current control method is put forward. The discrete current vector is obtained through the discrete with certain cycle for the stator current vector composed by the three phase current in electricity Angle. The smaller step can be obtained by increasing the cycle, Which can effectively improve the positioning accuracy and suppress the commutation torque ripple.The discrete current waveform of the BLDCM is square wave, The quality of the waveform directly affect the control performance of the motor. The traditional PI, hysteresis current control strategy cannot achieve accurate current tracking, The rolling optimization strategy of predictive control can make the current get good following performance. Therefore, the transient discrete current step is used as the research object. The improved no beat current predictive control algorithm based on SVPWM for current optimization control is presented under the traditional no beat current predictive control. The optimal smoothing predictive voltage expression is calculated by using improved linear prediction method based on the guarantee that the current error equals to zero. Because the predictive control strategy is heavily dependent on inductance parameter, the control precision will decrease when the inductance parameter is mismatched,so the inductance online identification algorithm is adopted combining with the characteristics of discrete current square wave, using the mean filter and the positive and negative half cycle real-time sampling of the winding inductance to solve the bad performance caused by the inductance parameter mismatch.After determining the current control scheme, the control system based on the DSP is built to realize the function. It includes two parts: control and power part.In addition, the isolation circuit and the overvoltage and under-voltage protection circuit is designed in order to improve the reliability of control system, which lay a good foundation for experimental verification.Simulation and experimental results show that no beat current predictive control of BLDCM based on improved discrete current control strategy has good control performance, the system has a good positioning and speed control performance, it can effectively improve the positioning accuracy and reduce the commutation torque ripple, thus lay a solid theoretical basis for the BLDCM in high precision position servo control system.