Research On Control System For Brushless DC Motor Power Steering Of Automobile

Electric power steering system directly affects the stability and safety of the vehicle.It's performance depends mainly on the motor and it's control algorithm.The performance of brushless DC motor(BLDCM)with full-width concentrated winding is much better than that of brushed DC motor,and the complexity and cost are lower than that of permanent magnet synchronous motor with distributed winding,but it is rarely used in electric power steering system.Related research is weak.Due to the high cost performance,brushless DC motors will be widely used in automotive power steering systems.Therefore,combining with the performance requirements of automotive power steering system,the research on brushless DC motor control system has both potential engineering application value and certain theoretical value.In this paper,from the perspective of control system economy and reliability,BLDCM with Hall position sensor and BLDCM without position sensor are selected as research objects.According to the characteristics of motor assist torque proportional to motor current,the steering assist characteristic is satisfied.Based on the requirements,the BLDCM steering assist control system was studied by theoretical analysis,computer simulation and experiment.The main work content and results are as follows:1.In the conventional proportional-integral-derivative(PID)control strategy adopted for assist control and return control,a neural network with optimized PID coefficients is proposed due to the slow response caused by the unreasonable selection of three PID coefficients.The PID assist control and particle group PID back-control strategy were established.The dynamic model of the vehicle electric power steering system and it's corresponding Simulink simulation model were established.The simulation was carried out in combination with the CarSim vehicle model.The neural network PID assist control and particle swarm were verified.2.For the BLDCM power steering system with Hall sensor,combined with the steering assist characteristic requirements,the three closed-loop control algorithm of SMC speed loop and double PID current loop is used to analyze and simulate the speed and torque response of BLDCM.The system hardware and the electric power steering experimental platform were tested.The research results show that the BLDCM with Hall sensor can be used for the steering assist of the car,which can produce the expected power-assisting effect,and the motor control algorithm is feasible.3.Theoretical analysis and simulation analysis of the initial positioning,starting,speed regulation and torque control process of the motor rotor in the position sensorless BLDCM power steering system,the motor control program is compiled,the experimental platform of the motor control system is built and the position is not set.The sensor electric power steering experimental platform was carried out and corresponding experiments were carried out.The results show that:1)The position sensorless BLDCM can also produce the proper power-assising effect in the power-assisted system;2)The new rotor initial positioning algorithm based on the motor-line current sequencing based on the position-free sensor BLDCM is more accurate than the previous literature.The algorithm is more efficient and accurate,and the number of sorting is reduced from 7 times to 5 times.3)The new algorithm proposed in this paper to control motor start-up by detecting the motor line current difference before and after motor sector switching is more effective than the previous paper,the algorithm is simpler and more practical.