Modeling And Control Algorithm Reserch Of Electric Power Steering System

The developing process of steering system has experienced several phases from the simple Mechanical Steering System, Mechanical-Hydraulic Steering System to Electric-Hydraulic Steering System, till the Electric Power Steering System (EPS) with lower energy consumption and higher performance. The EPS is applied more and more widely in the automobile industry, which is led by its advantages over the traditional hydraulic power steering systems in safety, environmental protection, engine efficiency, flexibility of installation, and easiness on the adjustment. In recent years, EPS got lots of successful applications in some foreign countries, while the domestic products are still in the developing phase. It is a hot topic and owns a promising future.In this paper, the characteristics of EPS, operational principles, and structures are discussed and the current domestic and abroad research situation is addressed; by analysis of dynamic, kinematics and load characteristics of EPS, a mathematic model of mechanical steering and EPS is established by using Newton law and the related physical principles and the impact of the mechanical parameters on the system characteristics is addressed; the stability of EPS is analyzed; the assist characteristic is analyzed theoretically and the determination of feature parameters for the straight-line assist are discussed.The conventional control method can only be used in the system with precisely built model and the single controlled target, but the EPS is non-linear and multi- input and output system, which makes it difficult to keep the satisfying performance by the controller designed by the conventional method when the errors are introduced by the alteration of system parameters, the interference, and the simplification of model. Therefore, in order to guarantee the system performance, the closed-loop system must have robustness. Based on the studies of mathematic modeling and the assist characteristics, the boundary conditions for different control algorithm are addressed in terms of different steering operation, in which the key research includes H∞Assistant Control Algorithm, Return Control Algorithm, and Damp Control Algorithm.In view of the existing of friction torque and rotational inertia in EPS system, which significantly affect the return of tires and lead to the stickiness with the decrease of assist following, the friction compensation, damp compensation and inertia compensation are introduced to solve the above problems. At last, the stability of EPS is analyzed.Based upon the above studies, a pure digital simulation platform is established. The simulation results prove that the mathematical model is correct. The control algorithm adopted takes a tradeoff among the assistant characteristic, the return characteristic, the damping characteristic and the robustness. In order to realize functions of the system, an EPS controller is designed. The system hardware includes the D.C. motor drive circuit, the current measure circuit, the sensor interface circuit, the alarm, and the relay drive circuit. The system software takes the MPLAB-IDE debugging environment as the platform, adapting the block design method in C language.