Research On Modeling And Control Strategy Of Electric Power Steering System

The Electric Power Steering system is the foundation of a new generation of intelligent steering systems.Its research and development are in line with the three major themes of safety,environmental protection and energy saving in the development of automobiles,and has very realistic and long-term significance.It has many unique advantages and a broad market.This article focuses on the EPS system modeling,control strategy,and controller design and testing: Firstly,the system is modeled according to the working mechanism of the actual EPS system,and it is verified by real car test;Secondly,design control strategy and controller based on model,and study the composition of control strategies and the design of basic assisted control strategies,and optimize the system's torque control loop based on system transfer characteristics and disturbance analysis;Finally,the effectiveness of the control strategy and the controller and the performance of the EPS system were verified by repeated tests on the bench and the real vehicle.The main tasks as follows:(1)According to the transmission route of steering power,the EPS system model including steering mechanism and wheels was established.According to the operating mechanism of EPS system,the system transfer function is derived.Finally,the frequency response analysis of EPS system based on frequency characteristic test proves the correctness of the proposed model.(2)Aiming at the requirements of vehicle steering function and performance,according to the design idea of modular control,a basic power-assisted control strategy consisting of a torque control loop and a current control loop is proposed.The control effects of the torque control loop and the current control loop are verified by experiments.(3)In order to obtain a better steering feel,the boosting gain of the EPS system is generally designed to be variable,and the transmission characteristics of the system vary with the gain of the boosting force,thus the controller is required to have strong robust performance.The boosting gain varies with the change of the torque sensor signal.Therefore,the variation of the torque sensor signal is taken as the main disturbance of the system.The feedforward controller is designed to compensate the main disturbance,and the parameters of the second-order feedforward controller based on the internal model control structure are optimized by using the system uncertainty analysis and robust control theory.The design goal of robust feedforward controller is proposed,a second-order feedforward controller with good robustness is obtained by solving the optimal algorithm.In order to solve the problem that the second-order feedforward controller can not have good control effect in both high frequency and low frequency range,a high-frequency gain compensator is added to improve the control effect of the controller in high frequency range on the premise of ensuring the control effect of the controller in low frequency range.(4)The effectiveness of the EPS system control strategy and controller was verified on the bench test system;the performance of the EPS system was verified on the real vehicle test system.The test results show that the EPS system studied in this paper has good low-speed steering portability,high-speed steering stability,and torque ripple suppression performance.