Optimization Control Strategy For Electric Power Steering System

With the development of technology, and the increase of people’s requirements on the the vehicle maneuverability, EPS(electric power steering) system became the research focus of vehicle steering system because of its unique advantages quickly.EPS system compared to the current mainstream hydraulic power steering system, its advantages is reflected not only in the structure is more simple, to overcome the hydraulic system oil leakage of the inherent defects, and due to the adoption of the motor as a power source, more easily to control and can effectively solve the contradiction of low-speed steering and speed to "light" and "spirit". Moreover, the EPS system works only when steering, compared to the hydraulic power steering system is always in the working state, can greatly improve the energy efficiency and save energy.In this paper, based on the proper simplification of the mechanical structure of the electric power steering system, the dynamic model and Matlab/Simulink simulation model were established respectively for steering wheel, input shaft, torque sensor, assistant motor, retarding mechanism, output shaft, rack and front wheel. Meanwhile, the whole vehicle simulation model is established in Carsim. After analyzing the working characteristics of the EPS system, the power control mode is including three types: power control, damping control, return control. Then based on the analysis of the mainstream current control strategy: the traditional PID control and fuzzy adaptive control, to improve, with the genetic algorithm’s advantages of intelligence, parallelism, only to objective function as constraint conditions and without the continuous micro, easy to implement and so on, put forward a method based on genetic algorithm to optimize the PID parameters optimization control strategy. After analyzing the basic operation and advantages of genetic algorithm, the fitness function, selection method, cross method, variation method of genetic algorithm are determined. Then set the conditions in accordance with the relevant national standards with CarSim vehicle simulation model and EPS’ Matlab / Simulink simulation model, simulation verification in four angles as the steering wheel angle, yaw angular velocity, body side angle and lateral acceleration. After verification, the proposed control strategy is effective, improve the vehicle handling stability and ride comfort, help to improve the vehicle driving experience.After the simulation, according to the control strategy proposed in this paper, the overall control scheme is worked out. Produced the controller based on single chip microcomputer TMS32, and adopted the H bridge driving circuit based on STL293 to control the power assisted motor. At the same time, taking into account the non-contact sensor relative to the current EPS system mainly adopts the contact type sensor has the the advantages as can effectively avoid the impact of dust, relatively low manufacturing precision and environment requirements, can realize the non-contact measurement of linear displacement and angular displacement in a simple, compact space. The prototype uses HELLA non-contact sensor(HELLA inductive position sensor), and to build an experimental platform. Tests were carried out for the prototype in current characteristics, input / output characteristics etc. The experimental results show that the prototype meets the national standards, and it is a commercial EPS system.At the end of the article, the research of the topic is summarized, the innovation points and deficiencies of this paper, and the next step of research and work put forward the direction and objectives.