Research On Commutation Torque Ripple Suppression Of Brushless DC Motor Based On Fault Tolerant Control

With the rapid development of electric vehicle industry, the drive motor control system has become a hot research topic in the world to meet increasingly more performance requirements. Because of the high efficiency, low cost, small volume and so on, the permanent magnet brushless DC motor is considered as the ideal choice for the drive motor of electric vehicle. This paper takes the permanent magnet brushless DC motor as the research object, both commutation torque ripple suppression method and fault-tolerant control were studied based on the square wave control strategy.Firstly, the mathematical model of permanent magnet brushless DC motor is established, with the square wave control strategy described in detail, as well as the control system diagram of the permanent magnet brushless DC motor torque control system is presented.Secondly, the generated mechanism of permanent magnet brushless DC motor commutation torque ripple is analyzed, and the effect on commutation torque ripple of different PWM modulation measures is explained in detail. Through deriving the mathematical model during the commutation period, a novel commutation torque ripple suppression method based on overlapping commutation and current prediction control strategy are proposed, aiming to break the limitations of existing methods to suppress the commutation torque ripples. The control method not only extends the motor speed range where the commutation torque ripple suppression method is effective, but also has the advantage of insensitive to the inductance parameter of the motor. In the realization of this method, the predictive current compensation method is given, improving the effect of the current control. The effectiveness of the control strategy is verified by simulation.Thirdly, the fault types of three-phase inverter are introduced, selecting the open circuit fault of the inverter as the research object. Fault diagnosis method based on line voltage detection is used to detect the inverter fault of permanent magnet brushless DC motor. In this paper, several fault tolerant control schemes are compared, and the operation principle of the three-phase four switch inverter is emphatically described. Based on the fault-tolerant control scheme, a three-phase four switch fault-tolerant control strategy is proposed, which can reduce the current fluctuation by adjusting the PWM modulation mode. The feasibility and correctness of the proposed control method are verified by simulation.Finally, a permanent magnet brushless DC motor fault-tolerant control system hardware platform is built with the Freescale DSP chip MC56F8247. The software modules of commutation torque ripple suppression and fault tolerant control strategy are built. The control algorithm is written, and the software and hardware debugging of the system have been completed. The experiments verify the feasibility and effectiveness of the scheme proposed in this paper.