Research On Current Optimal Control Method For Power Steering Motor

In recent years,Electric Power Steering system(EPS)has gradually replaced the traditional steering system because of its simple structure,energy saving,miniaturization and other advantages,and occupies a dominant position in the market.EPS is a typical vehicle-mounted torque servo system.In order to cope with complex driving environment,there is a high requirement for output torque.Considering the direct relationship between motor torque and current,it is especially important to optimize the control of motor current.Current EPS systems usually use dual mode control structure,but there are still some deficiencies and optimization space in the following and fluctuation control of motor current.Specifically,in normal driving mode,the motor is controlled by current loop with maximum torque-current ratio,and its control method usually has the problem of slow current response and poor follow-up.In the emergency turn mode,the motor enters the speed ring control and adds a magnetic weakening algorithm to achieve speed expansion.The related control pays more attention to speed tracking and ignores the target current fluctuation.For this reason,this paper is based on the following and fluctuation of current.Based on the basic control of EPS motor,the corresponding current optimization control algorithm is studied.The main work of this paper is as follows:Comparing different types of boost motors,permanent magnet synchronous motor is selected as the target motor for this study,and the mathematical model and vector control model of permanent magnet synchronous motor are analyzed.The resistance moment of EPS system is modeled and analyzed to provide reasonable load characteristics for subsequent motor control.Aiming at the current following problem of EPS in normal operation mode,a deadbeat predictive control algorithm is introduced to solve the problem of slow current response in traditional proportional integral control.The stability range of the motor considering time delay is derived and the static current difference problem is quantitatively analyzed.To deal with the delay problem and the current static error problem,a sliding mode observer is designed to observe the current and disturbance.A new switching function is introduced to weaken the chattering problem of the sliding mode observer.The proposed algorithm is validated in a simulation model.Aiming at the current fluctuation problem in emergency steering mode,a simulation comparison was conducted between the negative direct-axis current compensation method and the variable quadrature axis single current regulator method.The former was selected as the basic field weakening method,and a hybrid field weakening control method was introduced to improve the field weakening performance of the motor.A linear auto-disturbance rejection speed loop controller is designed to enhance the system’s anti-interference ability and reduce current fluctuations,and simulation verification is conducted.The hardware circuit design of EPS controller and the software program design of motor-driven are completed.On this basis,a motor test platform is built and the feasibility of the optimization algorithm is verified from the motor level.The joint simulation tests of Carsim and Simulink further prove that the optimal control algorithm has good performance in EPS system.Software simulation and hardware test show that the current optimization control method designed in this paper can meet the basic requirements of EPS,at the same time,enhance current tracking ability,reduce current fluctuation,and optimize the motor’s torque output.It provides some ideas for the subsequent optimal development of motor control of EPS system.