Research On Control Of Electric Power Steering Based On Permanent Magnet Synchronous Motor

Electric Power Steering,referred to as EPS,generally selects a DC motor,which causes the whole system to be bulky,heavy in weight,and low in power.In order to reduce the overall quality of the steering system,this paper uses a Permanent Magnet Synchronous Motor,referred to as PMSM,with high power density,small volume and high efficiency as the power steering motor.In this paper,the sliding mode algorithm with strong robustness and fast system response is used to control PMSM.Aiming at the upper layer algorithm of EPS system,this paper optimizes the speed-assistance characteristic curve and designs the software and hardware of the EPS system.The EPS performance is verified by the corresponding testing experiments.The mathematical model of PMSM is established,and its mathematical model is simplified by Clark and Park transformation to facilitate the research of its control algorithm.In this paper,a variable switching gain sliding mode robust control algorithm is proposed,which combines system state variables and system external interference with switching gain to realize automatic adjustment of switching gain and reduce system chattering.In addition,by adjusting the robustness coefficient,the external interference of the system can be overcome and the robustness of the system is enhanced.At the same time,the Lyapunov function is designed to prove the stability of the system.In addition,the proposed algorithm is compared with the traditional PI algorithm,and the simulation model is built in Simulink.The effectiveness of the algorithm is verified by simulation experiments.Three kinds of EPS power assist characteristic curves are introduced,and through the comprehensive comparative analysis,the straight line type is used to design the speed-assisted current.In order to improve the smoothness of the speed-assisted characteristic curve,the assist current is changed gently,and the steering feel is improved.The quadratic function curve is used to replace the part of the conventional linear assist characteristic curve which causes a sudden change in current.In addition,the exponential function is used to design the speed-assistance coefficient to obtain the speed-assisted characteristic curve in the full speed range.The Simulink model was built and co-simulated with Carsim.The simulation results demonstrate the portability of the steering at speed.The software and hardware design of the EPS system controller is carried out.The hardware includes the minimum system of the main control chip,torque signal,phase current acquisition,CAN communication,three-phase inverter,peripheral circuit of AD2S1205 chip and so on.The software includes variable switching gain sliding mode control algorithm,digital filtering,speed assist algorithm,motor drive,Space Vector Pulse Width Modulation algorithm and fault detection program.The corresponding experiments were carried out to verily the performance of the EPS,through the EPS system comprehensive performance platform.The three-phase inverter circuit control dead zone experiment,Space Vector Pulse Width Modulation algorithm sector judgment experiment and the target current tracking experiment verify the effectiveness of the motor vector control algorithm and the variable gain sliding mode robust eontrol algorithm.The torque sensor experiment,input torque and assist current experiment and input and output torque experiments prove the EPS speed-assisted characteristics,which can effectively reduce the driving burden.