摘要
电动助力系统采用电动机提供助力，具有转向力可变、路感良好、环保、耗能低和维修方便等优点，充分体现出汽车向智能化发展、满足未来安全性要求和环保要求的发展趋势。
本文在深入学习电动助力系统工作原理的基础上，设计了电动助力系统控制单元的硬件电路，研究了控制策略和算法，开发了相应的软件程序，印制了电路板，在自行搭建的试验平台上进行了实验验证。具体工作内容如下：
1. 研究了电动助力转向系统的发展和系统的基本原理；
2. 在充分考虑满足电动助力控制单元功能需求的基础上，开发了一套基于单片机80C552的电机控制方案：利用电子执行单元（ECU）实时采集信号，运用PWM技术实现对H桥和电动机进行电流闭环控制，并完成了硬件电路设计；
汽车转向系统故障
3. 在保证汽车的稳定性和安全性条件下，通过深入研究助力控制、回正控制和阻尼控制策略，提出了基于PID的控制算法，开发了核心控制程序；
上述研究工作实现了电动助力系统低速轻便、高速稳定的使用要求，为下一步的工程实用化奠定了先期技术基础。
关键词：电动机，PID，控制策略，PWM

Abstract
EPS is a kind of power steering system following the system of hydraulic, motor was adopted to offer power directly. EPS has many advantages such as adjusted power which is controlled by the automatically controlling unit，good way sense，environmental protection，low energy consumption, convenient maintenance. The development trend of intelligent vehicles, future security requirements and environmental requirements was fully represented by EPS.
In this thesis the Electronic Control Unit (ECU) and the software program of the ECU was designed, control strategies and algorithm were also studied based on the study of the op
eration principles of EPS. Following is the detailed process:
1. Basic components, working principle and mathematical model of Brushless DC Motor (BLDCM) were described in detail.
2. While the functions of ECU were considered, a scheme of motor control based on the high-performance microcontroller 80C552 was put forward and the ECU was designed. PWM technique was used to control H and closed loop motor current.
3. Three control strategies which are assisting mode return ability and damp mode to get a stable steering under various conditions was presented and discussed in this paper. And a control algorithm based on PID was proposed under the strategies.
The research above make the A/D acquisition program, speed signal acquisition program of the Electric power steering system come true, and t it laid a practical basis for the next preliminary technology.
Keywords: MOTOR; PID; Control Strategy; PWM