Research On EPS Control System Based On Fuzzy Strategy

At present,with the rapid development of automotive electronic technology, people's requirements of vehicle such as vehicle manipulator, comfort, safety are also increasing. In order to guarantee the vehicles have better manipulability, stability and portability in any conditions, scientists are continuously improving Steering Control System. At present, for the purpose of improving handling Stability, safety and comfort, the electric power steering system has become one of the hot spots in the automotive electronic control technology of world.In the traditional areas of control system, the dynamic model will influence the control performance as the first key factor. However, for complex control systems, it is often very difficult to accurately describe the precise mathematical models. Fuzzy control technology is one of the control methods to make control process intelligent, it doesn't need the precise object model, and has strong robust, especially is suitable for nonlinear, time-varying and delay control systems such as automotive electric power steering control system and so on.With the research status of current automotive electric power steering control system improving, the control algorithm of output target current, hardware circuit design, computer model simulation and experimental analysis of Fuzzy Controller have been carried out in this papers. the problem of target current output in any conditiong that the speed is constantly changing is solved. and the following conclusions are summarized:1. The overall design programme of EPS control system is determined. In this paper, with a great deal of access to the relevant literature, a clear understanding about the research on the electric power steering system mostly concentrated in the motor current feedback tracking,which mainly using traditional PID control method as control strategy.The theoretical basis of this control algorithm is ideal motor power characteristic, it can only give the current targets in the discrete input speed signal,which makes the power steering process less delicate and sensitive enough. At present, due to the product cost and other aspects of technology shortcomings, EPS has not been widely used, only be configured in some high-end cars. Therefore, fuzzy control strategy to confirm target current is adopted in this paper, and PID controller is utilized to tail after target current to achieve closed-loop control. 2. The basic structure of Fuzzy controller is determined.According to the nonlinear relationship between target current and speed on the actual traffic course of vehicles, an fuzzy controller that can meet the power characteristic in arbitrary speed is needed to design,which also be suitable for multi-input and single-output control system. After A/D conversion, the torque signal of steering wheel and the speed signal are input to the electronic control unit ECU, the fuzzy controller finally give the current target according to certain fuzzy control algorithm. The electric power steering system using permanent magnet DC motor, torque is output to the Armature current proportionally. Therefore, it can be converted to control the current to achieve the target goal of controlling target torque instead. Clearly, the process of EPS working mainly solve two key issues: the first is identifying target current, and the second is tracking target current.3. Fuzzy controller design. It is different from conventional controller, fuzzy controller design need not using differential equations, transfer function, equation of state and other precision mathematical description,but by definition of variables, fuzzy sets and the corresponding membership function by a group of fuzzy language to describe the mapping relations between input and output.In the fuzzy control system,the key of making input fuzzy is to determine its membership function of the fuzzy sets.In this paper,we use triangles membership function make input and output variables fuzzy.The chapter also set up fuzzy control rules combined with expertise and accumulated experience to form the fuzzy look-up table.Finally.Beside,in order to complete the fuzzy controller design,it use the method of largest membership function to control the final output.The chapter also established the computer simulation mode of EPS Fuzzy Control System,tested its rationality and effectiveness of the control rules by simulation analysis.4. Hardware circuit design of fuzzy controller. Microprocessor is the core and critical part of control system, it need not only to deal with a large number of input and output signals, but also to achieve high-precision real-time control. Therefore, in this paper, P87LPC768 single-chip microcomputer is chosen as the control chip of this fuzzy control system, which has 20 feet .Beside, it slso can reduce costs and improve system performance. A permanent magnet DC motor is also chosen as execute components of EPS control system in this paper, and the motor drive circuit is designed. SCM can not directly drive high-voltage and high-current devices, in order to control the operation of the motor, the power driver circuit between the I/Oport of SCM and motor is designed in this paper. In the motor drive circuit, PWM control signal of its own is used, and dedicated three-phase bridge to driver chip IR2130 are used to drive the reversible PWM H-bridge circuit.In addition, anti-jamming of the hardware circuit has be designed. It also achieved the the high-voltage,over-current protection and other security by the self-protection function of IR2130.5. Its rationality should be verified through test bed after a control system design is complete. However, due to the lack of laboratory equipment, EPS test bed can not be established; The lack of control object, the output signal acquisition and feedback can not be achieved. Therefore, in order to verify the effectiveness of fuzzy controller, in this paper signal generator is used to replace EPS fuzzy control system speed and torque input, after accounting under the look-up table, it finally received assistance motor power current. In the experimental process, it does not really work in complex environment, so 8-bit AT89C51 MCU is chosen to replace P87LPC768 single-chip microcomputer. In the experiment, the clock and reset circuit, the input signal and A/D converter circuit, the output signal and D/A converter circuit have also been designed. In the end, compared the experimental output curves with simulation results, it can take a conclusion that the control signal at the core of fuzzy controller are similar with simulation results.6. Software design. The software design of fuzzy control system mainly includes the main program, sampling module, A/D module, fuzzy logic module, etc. Concluded with the thinking of software design, the main program flow chart and A / D converter subroutine flow chart are drawn in this paper.