Research On Fuzzy Self-adaptive Proportion-integral-derivative Control Strategy At Distance Downstream Bottlenecks

With the increasing number of motor vehicles and limited freeway resources,problems such as traffic congestion and traffic accidents occur on freeways.In order to improve freeway traffic efficiency and reduce traffic accidents,research on freeway active traffic flow control strategies is also underway increasingly developed,two of the more widely used in engineering practice are ramp metering control and variable speed limit control.When the traffic flow on the freeway is in congestion,the monitoring of the ramp metering can avoid the increase of traffic congestion,quickly eliminate the congestion,and reduce the delay.Variable speed limit control has a good performance in solving the problem of the difference in the traffic volume between the bottleneck section of the upstream and downstream（that is,the section where the lane is closed and the traffic volume changes due to external disturbance）.In recent years,there have been many researches on the bottleneck sections of the freeway,but there are few studies on the long-distance downstream bottlenecks of the freeway,which restricts the development of the active traffic flow control strategy of the expressway.In many actual highway scenes,due to the phenomenon of downhill slopes,bends,tunnels,bridges,and lanes in the downstream,there will be a bottleneck in the downstream capacity than the upstream.In this case,it is recommended to use the traffic flow from the downstream bottleneck instead of the upstream control area as measurements,because there is a non-negligible time delay between the action in the upstream control area and its impact on the traffic flow dynamics at the bottleneck location,Therefore,the controlled variable cannot reflect the disturbance encountered or suffered by the system in time.Even if the signal is detected to cause the controller to operate,it takes a delay time for the controlled variable to be controlled.In this way,the system will inevitably go through a long adjustment time and produce obvious overshoot.The control difficulty of the controlled system with the delay characteristic increases with the increase of the degree of lag.This situation has high requirements on the ability of the control strategy to cope with time delay,and it is worthy of special attention in the design of highway active traffic flow control.The current traffic flow control strategy is to consider the control area as the main consideration.It is difficult to eliminate the reduction in control effect caused by time delay.The control has limitations.This article focuses on improving the capacity of long-distance downstream bottlenecks to improve the overall operation of the highway Efficiency is very important.From the perspective of engineering application,the thesis research is helpful to improve the highway traffic management level of our country and improve the efficiency of highway traffic,which has important engineering application value.In view of the traffic flow characteristics of the long-distance downstream bottleneck of the expressway,this study proposes a fuzzy self-adaptive proportional-integral-derivative（PID）control strategy,which has a good control effect on the non-linear and hysteretic control system.For entrance ramp control and variable speed limit control,the control strategy consists of proportional-integral-derivative（PID）control and fuzzy control.The design of fuzzy adaptive PID controller is realized in Matlab.The fuzzy rules are used to adaptively adjust the parameters、₄)and₍（9） of the PID controller to keep the controlled object in a good dynamic and static stable state.In this study,the effect of highway active traffic flow control was evaluated through a traffic flow simulation model.The Cell Transmission Model（CTM）can simulate the accuracy of microscopic simulators in the traffic environment,while maintaining the advantages of the macroscopic model.In the face of the unique traffic flow phenomenon observed in periodic bottlenecks（such as reduced capacity）,cellular transmission The model can be well defined.The Cell Transmission Simulation Model（CTM）was built in Excel using Visual Basic macro language.It simulates the real-time running state of macroscopic traffic flow,the geometric characteristic parameters of highway,etc.,and simulates the key traffic flow characteristics and phenomena of highway.The fuzzy self-adaptive PID controller and the cell transmission simulation model are built as an interactive platform,real-time input and output of traffic flow data.In order to better simulate the control effect,three downstream bottlenecks of different distances were developed in the cell transmission model to test the control effect of the bottlenecks at different downstream distances.From the perspective of traffic operation optimization control,traffic operation time optimization control,and control of different downstream bottleneck sections,the fuzzy self-adaptive PID algorithm is compared with the capacity-demand control strategy and the proportional-integral（PI）control strategy in detail.The results show that,from the perspective of reducing the total travel time,the proposed algorithm reduces the total travel time by 41%to 43%in the stable demand scenario and 38%to 42%in the fluctuating demand scenario during entrance ramp metering.In variable speed limit control,the proposed algorithm reduces the total running time by 29%to 31%in stable demand scenarios and by 32%to 36%in fluctuating demand scenarios.From the perspective of traffic operation optimization control,fuzzy self-adaptive PID control is more effective than capacity-demand control strategy and PI control strategy.The research results also show that the fuzzy self-adaptive PID control strategy has the advantages of fast convergence speed,strong predictive ability,high action accuracy,etc.It has good adaptability to the system with time delay.In the case of a long-distance downstream bottleneck,a better control effect can be obtained.