Electric Power Steering System Based On DSP

In recent years, Electric power steering system (EPS), the future of automobile steering technology, has been developing rapidly and is becomimg one of the safe-critical systems in modern control system of cars. Automobile steering systems research has been going on for at least 30 years, efforts have been made to model steering system dynamics of automobiles in hopes of better understanding the entire vehicle system. Various control algorithms are derived in order to achieve the specified system characters.The EPS can realize adjusting steering, assist force according to vehicle speed and ensure the driver obtaining satisfied road feeling.In this paper, First I establish the mathematical model according to the steering system theory, then analyze the source of resistance and force, determine suitable control strategy. The fundamental function of EPS is to provide assistance torque, vehicle speed and wheel torque determine the size of assistance, the target value of motor current be calculate through Fuzzy Neural Network arithmetic. When the return torque is insufficient the system provide aligning torque to insure the wheel return to the balance position, The goal of damping control is to ensure the driver obtaining satisfied road feeling especially when the car is in a high speed.Control of motor is also very important in this paper, Brushless DC Motor is chosen in this design. Its control arithmetic is direct torque control, current signaln voltage signal,rotor position are needed in that arithmetic. Establish motor model by Matlab software to simulate DTC arithmetic in order to ensure this arithmetic will have a good performance in practical application.The core of EPS is control unit, in hardware, I chose DSP TMS320F2812 a product by TI company which is used in motor control, to undertake this task. Sensor signal must go through a conditioning circuit before DSP read. A/D correct program is designed to insure that the conversion number is accurate, also to improve the reliability of A/D model. The calculation process is a circulation process.The communication in car is based on CAN bus, in the purpose of share information, I designed CAN model to get speed and engine information from other node, EPS system sends voltage and wheel torque to the CAN bus.