Research On Eps Control Strategy Based On Robust Hybrid H2/H∞ Control

With the gradual application of Electric Power Steering(EPS)system in new energy vehicles and driverless vehicles,the performance requirements of EPS system are getting higher and higher.Due to the uncertainty of model parameters and external disturbances in the modeling process of EPS system,the vehicle handling stability and the robust stability of EPS control system are affected.Therefore,from the point of view of enhancing the robustness and vehicle handling stability of EPS control system,this paper designed an EPS control strategy with inner and outer loop double-layer structure.The main research contents of this paper are as follows:Firstly,the composition of EPS system is studied and its working principle is analyzed.The EPS system is simplified into four stress components: steering wheel,torque sensor,power motor and rack and pinion steering gear.The differential equations are established respectively by using Newton’s second mechanics law.According to the intermediate variables of the three,the comprehensive control model of EPS system was established,and the stability analysis of the comprehensive model was carried out,which laid the foundation for the design of robust controller.Secondly,through the analysis of EPS power characteristic,design a reasonable linear power characteristic curve;The vehicle handling stability is introduced,and the formulas of steering sensitivity and ideal yaw angular velocity gain are derived with yaw angular velocity and yaw angular velocity as evaluation parameters.It is proved that the steering model in this paper has appropriate understeer characteristics,which will lay a foundation for the subsequent design of robust controller performance indicators.The problems existing in EPS system are analyzed,and the main control objectives of this paper are to improve steering portability,steering "road sense",following performance,robust stability of EPS and vehicle handling stability.Thirdly,the two-layer structure control strategy of EPS system is proposed.In the outer loop control,for road interference and sensor noise,the control effects of power following,"road sense" and handling stability under H2 control and H∞ control are compared.According to the comparison results,a hybrid H2/H∞ controller was designed by choosing H2 and H∞ norm control channels based on the advantages of the two control strategies.Simulation results show that the proposed hybrid H2/H∞ control strategy can meet the control objectives in this paper.In the inner loop control,the PID control strategy based on the nominal model disturbance observer is proposed for the perturbation of the model parameters and external disturbances of the motor.Compared with the traditional PID control method,the results show that the PID control strategy based on the nominal model disturbance observer has better anti-interference performance and current tracking performance.Fourthly,the performance of the two-layer control strategy is verified by co-simulation with Carsim and Simulink.According to the national standard ‘Vehicle Handling and Stability Test Method GB/ T6333-2014’,the corresponding handling stability test was carried out on the established co-simulation model.The test results show that the dual-layer EPS control strategy designed in this paper has good steering portability,handling stability,assist following performance and robust stability.