Research On The Control Strategy Of 6-Phase Brushless BSG Motor

Compared with the traditional vehicles, the electric vehicle has the advantages of saving energy and emissions reduction. Because of its low cost and is especially suitable for city traffic, the hybrid electric vehicle equipped with BSG system is widely concerned. But the existing three-phase brushless BSG(Belt Driven Starter /Generator) system has disadvantages of large torque ripple and starting torque is insufficient. Compared with the traditional three-phase BLDCM, the six-phase BLDCM has advantages of small torque ripple, large starting torque and fault-tolerant capability, is especially suitable for Electric cars, which has higher request for the system stability and reliability. Based on the six-phase brushless DC motor as the research object, the square wave control, sine wave control and fault-tolerant control are studied and the test is done in six-phase brushless BSG experiment platform.1. Based on the research of three-phase brushless motor, the structure, working principle and mathematical model of six-phase brushless DC motor are discussed and build the ontology model of six-phase brushless DC motor in MATLAB, which laid the foundation for the follow-up study of the motor control strategy.2. On the analysis of the cause of the brushless motor torque ripple, the torque ripple of the three-phase and the six-phase BLDCM are compared. Choosing the PWM_ON modulation to drive motor in MATLAB. At the same time, under the condition of no-load and load conditions, the simulation results of current, torque and speed waveform of six-phase and three-phase brushless motor are analyzed. Results show that utilizing the square wave control, the torque ripple of six-phase brushless motor is smaller than the three-phase brushless motor.3. In order to further reduce the six-phase brushless dc motor torque ripple and improve the utilization rate of the dc voltage, the space vector modulation method are used in brushless dc motor control strategy. Through the simulation, analyzing the six-phase BLDCM’s torque and current waveform under the control of square wave and sine wave and the three-phase and six-phase BLDCM’s torque and current waveform under the control of sine wave are also analyzed. The results show that the six-phase BLDCM’s torque characteristic under the control of sine wave is the best.4. The single-phase fault-tolerant control for the six-phase BLDCM is studied. Based on the round rotating magnetic field of the theory of multiphase motor, the rest of the five phase winding current of six-phase BLDCM is deduced by using the method of comprehensive vector. The values are imported to the fault-tolerant control system model on MATLAB simulation platform.Through the simulation, current and torque waveform of six-phase BLDCM under the fault-tolerant operation and normal operation are analyzed, the results show that under the fault-tolerant control strategy, the motor can run normally.5. For six-phase brushless BSG system, the hardware platform of driving and sampling are set up. On this basis, a experiment is carried out using laboratory existing motor, this verify the feasibility of design scheme. Laid the foundation for the subsequent six-phase brushless BSG system experiment.