Research Of Electric Power Steering System With Sliding Mode Control

Steering system is one of the important systems of car, directly related to the car’smaneuverability. EPS system can reduce driver’s efforts, providing a safe andcomfortable experience.Electric power steering system (EPSS) is a nonlinear time-varying system withseveral inputs and outputs. In actual process, it is easily affected by changes of theparameters,external interference and sensor measurement error and noise, etc.At the same time, goals are set for EPSS. EPS must be able to quickly andaccurately provide assist torque. EPS must be able to eliminate vibration of systems,EPS must transmit road information to driver and has a good anti-interference ability.Many other requirements. Therefore, control of electric power steering system is acomprehensive and challenging topic for engineer.The main work of the paper are as follows:Models of EPSS and vehicle are set up. And a state space equation is used for thissystem.Uncertainty of EPSS is described.As sliding mode control is easy to implement with rapid response to the input,sliding mode control (SMC) is chosed to design the controller of the electric powersteering system to ensure desired assist torque and motor’s rapid response to the drivercommand.EPSS must also be robust to model errors, parameter uncertainties and outsidedisturbances. The simulation results show that SMC of EPSS can do all this except thatEPSS is under influence of the large magnitude disturbance. A disturbance observer isdesigned for the motor to estimate the changed voltage yielded by the torque ofinterference. Sliding mode control of EPS with this observer can eliminate or evenweaken the influence of outside interference.Road feel of EPSS is also analyzed. There exist mutations of road feel intensity ofEPSS when the straight line or inflexion line is used as boost curve of the system. Andto aviod the mutations to get nice road feel，the sineline which is one type of thecurvilinear with sliding mode control strategy is chosed. Methods are aslo proposed toimprove road feel for steering system from the perspectives of transfer function of roadfeel and state space equation.A sliding mode controller combined with disturbance observer of the motor and the boost curve of sine type is designed in order to achieve basic control objectives evenwhen the system is confronted with uncertainties inside and outside.