Research On Steering Motor Control Of Active Rear Wheel Steering System Of A Car

With the development of society,the "new four modernizations" of automobiles have become the pursuit of the entire industry.The realization of electronic steering intelligent control for active steering can improve driving characteristics,steering stability,and safety.This paper focuses on the research of steering executive motor control algorithms,controller functional safety analysis,active rear wheel steering strategy,and experimental bench testing,etc.,which designs and develops actuator for ARS systems.Relying on the mathematical model of the PMSM,the decoupling control is completed by decoupling the torque and the excitation current through coordinate transformation.According to the field oriented control principle,different control strategies are discussed: id*=0 control,MTPA,constant flux linkage,and field weakening control.In addition,SVPWM technology is analyzed in detail,and the model is built.Aiming at the motor three-closed-loop FOC algorithm,based on the traditional PI control,a three-closed-loop PI controller was established,and then the FOC algorithm was improved based on the three-step nonlinear method principle,and the three-step current control,speed control,and position control were established.At the same time,the voltage and current limit circle,MTPA,and MTPV equations are established to build the optimal trajectory decision algorithm for field weakening control.Finally,the model was built and the simulation experiment was completed.By comparing the three-step method with traditional PI control,the current,speed,and angle of rotation were obtained respectively.At the same time,the simulation experiments of the field weakening control verified the rationality of the field weakening speed expansion algorithm.The results verify the control effect of the three-step method: faster dynamic response speed,less steady-state fluctuations,and its control effect can meet the ARS actuator’s position and angle following,and fast steering characteristics.In order to prevent damage to the controller and even injury to the actuator due to failure of the actuator,the safety objective of the motor control function is determined to prevent the ARS from performing non-command abnormal rotation of the motor.Based on MCU,predrive chip,and system basic chip,the controller schematic diagram is designed and developed.At the same time,a fault tree is established for abnormal rotation faults and FEMA analysis is performed.The motor drive circuit fault is divided into three major modules: voltage source,driving bridge,and pre-drive chip.Summarizing the failure forms of different types of signals in each module according to the influencing factor analysis method,and the failure behavior is set according to the Err Flag of the pre-drive chip.Finally,the detailed design of the diagnostic response strategy is completed from two aspects(pre-drive chip security mechanism,MCU monitoring and logic diagnosis).Aiming at the ARS upper layer strategy,a two-degree-of-freedom four-wheel steering dynamic model is firstly established,and common control strategies of the ARS system are discussed: proportional feedforward of front wheel turning angle,PI control of yaw rate feedback.After that,taking the best steering characteristics as the control target,based on the linear quadratic form(LQR)theory,the LQR controller was established using feedforward + feedback.Considering the tire cornering characteristics,taking the linear and non-linear operating conditions of the tire as the boundary conditions,taking proportional control + yaw rate PI control as part of the control law under the linear operating conditions,and setting the LQR strategy to two based on the linear and non-linear operating conditions.Setting weight coefficients for these three,and designing the optimal control strategy based on the three control law.Finally,the control strategy comparison simulation was completed,and the results verified that the ARS optimal control strategy has good control effect: it not only improves the dynamic response speed,but also guarantees the driving stability of the vehicle.In order to complete the closed-loop test of the bench,the hardware design of the active rear wheel steering gear was designed,and a stalled,dual-motor overhead,spring-loaded experimental bench and ARS-HIL experimental platform were set up.Different experimental conditions were designed,and the bench experiments were completed on the motor current,speed,and position following control.The experimental results show that the lagging effect of the actuator position is about 10 ms,which is slightly different under different working conditions,but all are within a reasonable range.At the same time,the effectiveness of the field weakening speed expansion strategy was verified,and the speed was as high as 4000r/min.In addition,this article finally puts forward the improvement direction of the research deficiencies.