Research On Permanent Magnet Drive Motor And Control Technology For Electric Power Steering Of New Energy Vehicle

The electric power steering permanent magnet drive motor has the characteristics of high power density and fast dynamic response,and has gradually become one of the important selections of power steering motor for electric power steering system(EPS).By analyzing the demand characteristics of electric power steering system for power steering motor and combining steering resistance moment under different vehicle conditions,a matching method of permanent magnet drive motor for new energy vehicle power steering is proposed.Taking a new energy vehicle as an example,the matching calculation of the motor is carried out,and the basic parameters of the booster motor are determined.Based on the analysis of common permanent magnet drive motor rotor magnetic circuit structure,a combined magnetic pole rotor magnetic circuit structure with hidden pole radial and oblique V shape embedded is proposed.According to the basic parameters of the PMSM,the main parameters of the stator,rotor and winding of the PMSM are designed and calculated under the guidance of the design method of the PMSM,and the double-layer winding structure of the integer slot with 4 poles and 12 slots is determined.Comparing the cogging torque of the booster motor under different pole deflection angles,it is determined that the minimum cogging torque of the booster motor is smallest when two pairs of V-shaped poles are deflected clockwise at 0.75 degrees.The electromagnetic characteristics of the booster motor under different loads are simulated and analyzed by finite element software.The rationality of the magnetic circuit structure of the motor is verified from magnetic field distribution,cogging torque,motor loss and output torque.The mathematical model of permanent magnet assisted motor in three-phase static coordinate system and two-phase rotor flux synchronous rotating coordinate system is established.Compared with different control strategies based on direct torque control,the maximum torque-current ratio control strategy is adopted to meet the requirement of good dynamic response of electric power steering system.Through in-depth analysis of the working principle of the maximum torque-current ratio control strategy,the control system model is built on the matlab/Simulink simulation platform.The simulation results show that the booster motor has high efficiency and good corresponding characteristics of torque and speed,which meets the design requirements.Based on the basic power curve,a power current control model including basic power,friction control,damping control and compensation control is established for different situations of motor power under different vehicle conditions.Combining the steering judgment model with the booster motor control model,the control model of the electric power steering system is built on the matlab/Simulink simulation platform.The simulation results show that the design of the basic boost curve is reasonable and the system responds quickly.It can provide obvious boost for the driver,alleviate driving fatigue,and achieve good correction effect at different speeds to ensure vehicle stability.