Research On Control Strategy Of Electric Power Steering System Of Asynchronous Motor

EPS system as a result of an innovative chassis technology, has the advantages of high efficiency, energy saving, controllable, working independently and so on, which also makes EPS become the inevitable trend of the development of the automobile steering system. However, DC motor of EPS system because of the disadvantages that the assist torque is small and cannot be applied in the senior car. This paper put forward a research in the control strategy of asynchronous motor EPS system, which was of great significance to increase the EPS application in the senior car.EPS system model is the basis for the study of control strategy. We used kinetic theory of mechanical to set two steering system models after DP-EPS system structure analysis according to the structure, So that it could simulate the function of EPS system more completely. The assist motor is the core component of the EPS system and in order to improve the system dynamic performance, a dynamic mathematical model of induction motor was established, including four functions, such as,the voltage, flux, torque and motion equation. However, coordinate transformation can make the complex model simple. After Clarke and Park transformation, the asynchronous motor can be equivalent as DC motor, which reduces the complexity of EPS control system and lays the foundation of control strategy for follow-up study.The control strategy of EPS system is a double layer control mode, in which the upper control is the power assisted decision control, and the lower level control is the control of asynchronous motor. Assist decision control is based on the assist characteristic curve. In this paper, we designed a compound type assist characteristic curve and power functions were designed respectively for high and low speed and large and small steering wheel torque. Simulation results show that the compound type of power assist characteristic curve is reasonable and optimal.Asynchronous motor is controlled based on rotor flux oriented synchronous coordinate of the vector control and under the premise of comparison to the simulation of several rotor flux observer model, we selected the current flux observer model based on the rotor flux oriented synchronous coordinate which was more suitable. The rotor flux and electromagnetic torque adopted voltage feedback decoupling PI control algorithm of asynchronous motor torque servo control, and two kinds of working modes of simulation results showed that the EPS system design was reasonable and feasible. We built the road sense and light of Gaussian type membership curve, and the curve more intuitive displays steering portability of difference and demand with different speed.we designed die spring equivalent substitution to resistance, and carried out the design of the hardware and software of the controller, completethe bench test. The experimental results showed that reasonable equivalent resistance, control strategies to ensure the torque following good.