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

With the further development of vehicle control technology,vehicle manufacturers have put forward higher requirements for electric power steering systems.In order to improve the performance of the electric power steering system,the corresponding steering system suppliers not only use the permanent magnet synchronous motor with higher performance as the assisting motor of the electric power steering system,but also has designed the system control algorithm.However,as far as the domestic research status is concerned,there are still many problems in the electric power steering system based on permanent magnet synchronous motors,such as system instability,hysteresis problem of rapidly steering,the steering wheel can not return to middle position after driver releases it,caton problem of slowly steering.So depth study of the control algorithm need to be done for the electric power steering system to improve vehicle's steering performance and driver's control experience.Focus on the electric power steering system based on permanent magnet synchronous motor,this paper mainly establishes a system simplification model that is relatively close to reality.Under high-speed operating conditions,by using the strategy of variable PI feedback control in flux weakening field,the output performance of the permanent magnet synchronous motor is improved.By analyzing requirement of active return,the performance of active return control is improved.And a signal injection method was used to compensate system friction.The detail steering system research and vehicle test work is as follows:1.Established a full-order model and simplified model of electric power steering system;The damping parameters in the upper part of the steering system are identified by changing the motor input voltage;and the system transfer function gain curve is obtained by injecting a pseudo-random signal into the system;through system parameters identification,two damping forms of tire are discovered;at the same time,the simplified steering system model has also been verified by transfer function fitting.2.In order to improve the operating performance of the motor,the mathematical model of the motor is established and the torque expression is deduced;The motor angle parameter is analyzed and optimized,and the parameter optimization effect is obvious.The SVPWM vector control algorithm of motor is studied in depth;based on the analysis of flux weakening and the optimal current running trajectory,the reason for the variable PI control in the flux weakening field is found,and then a variable PI feedback control algorithm is proposed;the motor bench test not only identifies multiple sets of PI control parameters,but also proves the feasibility of the flux weakening control algorithm proposed in this paper.3.The remaining issues about active return are analyzed,especially the coupling problem of basic assistance function and active return function;based on the analysis of legacy issues,the functional requirements of active return are clearly defined;under medium and low vehicle speed,state control and torque control algorithm of active return are designed based on the active return requirements.After several vehicle tests,the optimal values of the parameters in the active return algorithm are determined,and the optimization of the active return performance and steering fell is realized.4.Based on the analysis of the classic friction model of static friction + Coulomb + viscosity + stribeck,the friction characteristics of the steering system are studied,and a more realistic steering system friction characteristic curve is obtained.According to the friction characteristics of steering system,the friction compensation object is obtained.A simple friction compensation strategy of signal injection is used,and the optimal parameters' values of the injected signal are determined through vehicle test.The test result shows that the friction compensation method eliminates the steering caton under low and medium vehicle speed.