| The tractor is taken as the control object,the dynamic performance and disturbance attenuation ability of tractor path tracking are studied.Firstly,tractor position and angle obtained by the position and angle sensor are compared with the desired path,and then designs the gain switching nonlinear controller,reset controller(GFORE),tracking differentiator nonlinear controller.After that,the controller makes correct decisions and controls the actuator to drive the tractor to track the desired path.Finally,the design nonlinear method is compared with classic PID control method and FOPD control method under different tractor speeds.The results show that the controller designed can not only stabilize the tractor,but also overcome the performance limitations.In addition,the controller designed can improve the disturbance attenuation performance of the closed loop system.The main contents are as follows:1、A gain switching nonlinear controller of tractor path tracking is designed.The PID controller parameters by phase lead compensation is designed,then gain switching method is used to improve the response time of the system and the adjustable range of frequency further.At the same time,the proposed nonlinear controller is compared with the optimal PID controller and the fractional order PID controller.The results show that the gain switching nonlinear controller can not only make the rise time and adjustment time are shorter but also the overshoot of the step response is smaller.Meanwhile,the controller designed in this paper can improve the disturbance attenuation performance of the closed loop system.For the gain switching nonlinear controller,the practical application is carried out.The results show that the average tracking error of path tracking is 0.04m,the maximum tracking error is less than 0.11m and the average standard Deviation S.D.is 0.05m.The gain switching nonlinear control method can be used for tractor path tracking in engineering,meanwhile,the controller designed in this paper can improve the disturbance attenuation performance of the closed loop system.2、A reset controller(GFORE)of tractor path tracking is designed.By the controller’s algorithm and parameter setting principles,the controller state is designed by resetting the region state to control the system input.The results show that the GFORE controller can not only stabilize the closed loop system,but also overcome the performance limitations of the system with feedback control structure.Finally the system realizes no overshoot control and zero steady state error.By comparing the step response at different speeds,the GFORE controller can improve the disturbance attenuation performance of the closed loop system.For the reset controller,the experimental verification is carried out.The results show that the system realizes no overshoot control based on the reset control.Finally,the reset control method can be used for tractor path tracking in engineering,meanwhile,the controller designed in this paper can improve the disturbance attenuation performance of the closed loop system.3、A tracking differentiator nonlinear controller of tractor path tracking is designed.Nonlinear control is realized by arranging the transition process,extracting the output differential signal and designing the nonlinear combination of errors and their derivatives.In addition,the nonlinear controller is compared with PD controller and FOPD controller.The results show that the PD and FOPD controller can stabilize the system and improve the dynamic performance of the closed loop system,but it does not solve the contradiction between closed loop system overshoot and rapidity.Based on the nonlinear controller,the system can realize no overshoot and quickly track the desired path.At the same time,the nonlinear controller based on the tracking differentiator has robustness to the tractor’s speed change in the range of setting value(+10%).Therefore,the nonlinear control method improves the adaptability,stability and disturbance attenuation ability of the closed loop system. |
