| Electric power steering system has the advantages of Energy conservation and environment protection, easy control, what’s more, integration and intelligence of the control system can be implemented by EPS system and other electric control system of mutual communication. It is in line with the needs of the "Made in China 2025" times development, therefore research and development of EPS system will have important theoretical significance and practical value in engineering. On the basis of EPS controller, compensation control strategy of EPS is studied in this paper.Firstly, the dynamic models of the vehicle and steering system are established by MATLAB/Simulink which lays the foundation of the later development of EPS control strategy based on MC9S12XS128.Secondly, assistance curves of curve-typed are designed based on continuous road feeling. For EPS system with stronger time-varying and nonlinear characteristics, the single neuron self-adaptive PID control algorithm is adopted which is used to improve dynamic tracking performance of the motor current. Compensation schemes including torque differential, the friction, the inertia and damping are used to improve the dynamic response of EPS. On the basis of the compensation above, in order to solve jitter in situ after relinquishing hands on steering wheel, one control scheme of enlarging the assist dead zone based on torque change rate is put forward.Thirdly, scheme of EPS relinquishing hands return-to-center control is put forward based on the angle and angular velocity, and active disturbances rejection control algorithm is adopted which is used to improve the correction effect at low speed. Considering speed, torque and torque change.rate, high speed damping control scheme based on fuzzy strategy which is used to improve the driver’s road feeling in the situation of high speed. In addition, speed delay interval is proposed which is used to ensure two modes including power and damping of smooth switching.Finally, in order to verify the efficiency of the relevant control strategy, Simulink simulation, hardware in loop test and vehicle test are carried out. The power results by simulation and vehicle experiment show that the dynamic response characteristic is improved, the steering behavior is easier and road feeling is more continuous when compensation control is contained in EPS assistance strategy. The return-to-center performance by simulation and vehicle experiment show that effectively improve the vehicle return-to-center capability at low speed by active disturbances rejection control scheme. In addition, the high speed of damping control results by simulation and vehicle experiment show that the steering stability of EPS at high speed is improved by the proposed damping scheme. |
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