Electric power steering system

The invention discloses an electric power steering system. By means of steering assist motor output shaft turning angle signals and steering assist motor output shaft rotating speed signals of a motor output shaft position sensor arranged on a steering assist motor, left wheel speed signals, right wheel speed signals, vehicle speed signals and steering wheel torque signals, a current steering wheel absolute angle is determined through a current turning angle center position offset value self-learning algorithm, target assist torque is worked out with the steering wheel absolute angle as a required parameter, and the steering assist motor is controlled to output the target assist torque. According to the electric power steering system, no steering wheel turning angle sensor is needed, and cost is lowered while it is guaranteed that the high-precision absolute position of a steering wheel can be obtained.