With the vigorous development of autonomous urban rail transit signal system (hereinafter referred to as “urban rail signal system”) technology and the ever-expanding market demand, the development of urban rail signal system has reached a critical point. How to explore the development of next-generation signal systems based on the inheritance of existing technologies is the focus of heated discussions in the industry. This article starts from the perspectives of the occlusion system and system architecture, and through in-depth summary of the status quo and combined with relevant professional cutting-edge technologies, explores the next evolution direction of the urban rail signal system, and proposes system intelligent development suggestions to realize the “increasing efficiency of the urban rail signal system” , Reduce costs and improve intelligence.


| Current Status and Evolution of Blocking System

Blocking is a technical method to ensure that the train runs at a certain distance between the preceding train and the tracking train, and the blocking system determines the safety protection mechanism and forms the interval. The development of signal system has long been inseparable from the theme of occlusion system.

1.1 Current situation of occlusion system

At present, most urban rail transit systems adopt communication-based automatic train control system (CBTC), which is based on the principle of “retaining wall”, which protects the safety of subsequent trains based on the instantaneous position of the preceding vehicle, and realizes automatic train operation and automatic routing. Automatic functions such as row selection. The CBTC system uses the mobile block system to break through the restrictions of fixed block zones, and dynamically updates dangerous points in front of the train through real-time communication between trains and ground. From fixed occlusion to quasi-mobile occlusion, and then to mobile occlusion, the tracking interval between trains gradually decreases, as shown in Figure 1.


Figure 1 Schematic diagram of tracing of blocked train


Before the mid-1990s, my country’s urban rail transit mainly adopted fixed blocking systems, which usually follow the exit speed control method to protect trains from running safely. The braking start point is the end of the block area occupied by the current vehicle, and the braking end point is the block area occupied by the train ahead. The entrance of the first section at the rear forms a stepped grading speed control curve.


In the mid and late 1990s, the application of quasi-mobile obstruction in China gradually emerged. Compared with the fixed block system, the quasi-mobile block system has a positioning function added to the train, and the information transmitted between the train and the ground is more abundant. Therefore, its braking start point is dynamically determined according to the actual position of the current train, and the braking end point is the block occupied by the preceding vehicle The section entrance at the rear of the section is left with a certain margin to form a target-distance speed control curve, and the minimum driving interval has been significantly improved.


After entering the 21st century, the mobile block system has been widely used. Compared with the quasi-mobile block car-ground communication, it is more abundant, the train positioning is more accurate, and the braking end point is the tail of the front vehicle, and there is a certain margin. , Further shortening the minimum driving interval.


1.2 Evolution of Blocking System

Mobile blockade is currently the most mature block system for urban rail transit. On the basis of the mobile block system, if the speed protection curve limits the train tracking interval to be further broken, the distance between the front and rear cars in normal operation will be further shortened. Increasing the efficiency of line transportation and enhancing the flexibility of transportation organization have a huge promotion effect. By learning from the development of related industries, this article will provide a possibility for the evolution of the blocking system, that is, based on the traditional location-based tracking mode, the speed-based tracking mode and the coupling-based tracking mode are realized, as shown in Figure 2.


Figure 2 Three tracking modes of CBTC


In Figure 2, the CBTC-BL (Based Location) curve is a position-based trailing vehicle tracking curve, the CBTC-BV (Based Velocity) curve is a speed-based trailing vehicle tracking curve, and the CBTC-BC (Based Coupling) curve is based on The trailing curve of the rear car coupled with the car.


CBTC-BV introduces the speed parameters of the preceding vehicle on the basis of the CBTC-BL mode to realize the real-time speed tracking of the preceding and following vehicles to reach the limit of tracking. CBTC-BC introduces the concept of vehicle-vehicle coordination, which combines the virtual marshalling of the preceding and following vehicles to form a fleet for joint scheduling and operation, further shortening the operation interval and improving the overall transportation capacity of the line. It can be used in the morning and evening peaks. It is convenient to realize train formation to improve transportation capacity at any time, and quickly separate during normal peak hours. Without reducing the operating density, the short-form train operation will break the relationship between capacity and traffic density, achieve the purpose of “increasing efficiency” and make passengers more satisfied in travel.


In the CBTC-BC mode, two trains with the same running direction can be dynamically coupled. When a bifurcation point is encountered, the distance can be gradually increased to independently decouple and run independently according to different destinations. The coupling-based tracking mode breaks the current tracking bottleneck of the mobile block system, and realizes the further evolution of the block system on the basis of inheritance. Since the system retains the CBTC-BL curve, when there is an abnormal vehicle-to-vehicle communication and the CBTC-BC cannot be used, it can still follow the traditional mode to achieve continuous tracking in the CBTC mode.


| System architecture status and evolution

2.1 Current status of system architecture

At present, the system architecture of domestic lines mainly includes four parts: center, station, trackside and vehicle-mounted. This article focuses on optimization research around the center, station, and trackside architecture, as shown in Figure 3. At present, the three system architectures have inherited the development of national railways to a certain extent, based on computer interlocking (CI), and gradually superimposed equipment such as automatic train monitoring system (ATS) and zone controller (ZC), of which ATS is responsible for driving Command function, ZC undertakes mobile authorization calculation and train management functions. The equipment adopts a distributed deployment mode, which has little influence on each other, and equipment maintenance is relatively scattered. This kind of system architecture has high flexibility, but low integration, frequent information exchange between different subsystems, and communication delays are also greatly increased.


Figure 3 Schematic diagram of CBTC system architecture


At the same time, CI realizes the control of trackside equipment by driving the acquisition relay. In station equipment, combination cabinets equipped with relays occupy a large amount of equipment room area, which is not conducive to the upgrade and transformation of later signal systems; in the construction phase, the realization of relay circuits requires repeated checks by the site construction unit to ensure wiring If it is correct, the construction period will be prolonged; in the operation and maintenance, after the relay circuit breaks down, the inspection and disposal cycle is longer, which brings hidden dangers to driving safety.


In addition, with the continuous improvement of the automation and intelligence of urban rail transit, the architecture of the signal system is not conducive to the sharing of information between professionals, resulting in information islands for the signal profession, and the system architecture can be further integrated and optimized.


2.2 System architecture evolution


2.2.1 Digitalization of trackside equipment control

At present, the signal system adopts a centralized control method. Outdoor equipment is connected with indoor equipment through cables. Indoor equipment usually uses relay circuits to monitor outdoor equipment. Due to the physical limitations of cables, the control range is limited. Interlocking equipment must be installed in the station according to the area. The digitization of trackside equipment control is to replace the traditional relay execution circuit with the electronic execution unit to realize the co-location coupling relationship between the interlocking control part and the execution part in the setting, so as to realize flexible deployment:


(1) The interlocking control part can be set up either decentrally or centrally in the center or designated stations.


(2) The interlocking execution part can be distributed in certain stations as required, or can be centralized in outdoor areas.


Replace the traditional metal signal cables with optical fiber networks, and connect basic equipment directly to the general network through the electronic execution unit on the trackside, so as to control a single device or multiple equipment in a certain area, and realize the digitalization of trackside equipment control.


At present, in domestic projects, the interlocking system that uses electronic execution units to replace traditional relay execution circuits is mainly provided by Siemens, Bombardier and other foreign companies with core technology. Autonomous suppliers represented by CRSC have completed relevant research, and their results have been applied off-road, and actively promoted to the field of urban rail. This will greatly reduce construction costs, reduce maintenance investment, and alleviate existing lines. The difficulty of transformation has a profound impact and will also provide technical support for the evolution of the system structure.


2.2.2 Trackside integrated control system

The integrated trackside control system is a safety control system that combines the functions of ZC and CI equipment. The integrated design of ZC and CI optimizes the interface performance between the two devices, reduces the response time of the system, has higher availability and rich and flexible operation support functions, and is more conducive to the realization of efficient train control, as shown in Figure 4. Shown. Compared with the system without integration, the real-time performance will be increased by 50%, and the equipment integration will further reduce the space requirements of the equipment room.


Figure 4 Schematic diagram of trackside integrated control equipment


Research on integrated trackside control systems has achieved relevant results. On May 21, 2019, the Ministry of Science and Information Technology of China Railway Corporation, in conjunction with the Ministry of Industry and Electricity, organized a technical plan review meeting for the “train control and interlocking integrated system” in Beijing. Experts at the meeting believed that the train control and interlocking integrated system integrated train All the functions of the control center and the computer interlock, realize the full electronic control of the trackside equipment, reduce the number of equipment and interfaces, and conform to the technological development trend and the application and maintenance requirements of the electrical affairs profession.


As the trackside integrated control system integrates hardware, hardware costs are further reduced, the number of maintenance equipment is further reduced, and the real-time nature of system processing is further enhanced. While further reducing the cost, due to the reduction of the time delay in the system, the adaptability of the system on the 250 km/h line is further improved.


2.2.3 Flexible system structure

Through the above-mentioned system optimization, a full Ethernet control mode is realized. On the premise that the hardware and computing capabilities are met, the station equipment can be further integrated, that is, integrated trackside control equipment can be integrated into a station or centrally installed in the control center. At the same time, the ATS station equipment can be integrated with the central equipment to meet the requirements of conventional The deployment can meet the needs of centralized deployment, as shown in Figure 5.


Figure 5 Schematic diagram of system structure flexibility


Through the integration of equipment, simplifying the system architecture, fully distributing functions, and reducing the complexity of intermediate links and synchronization between equipment are the main characteristics of future technological development. CBTC based on vehicle-to-vehicle communication is a branch of this development idea.


2.2.4 Intelligent system function

The urban rail signal system has been developed to this day, and its degree of automation has been continuously improved, but the degree of intelligence has yet to be further explored and improved. At present, the hardware resources of each major of each line of urban rail transit are set up separately, forming an information island, which is not convenient for data integration and mining. Then, in the future, each major should gradually move towards centralized (oriented towards standardized components) based on a single business. ), virtualization (resource-oriented), cloud computing (support decision-making and provide value-added services). With the continuous development of technologies such as cloud computing and big data, the urban rail transit business will also expand in the direction of platform generalization, center virtualization, and station integration. The intelligentization of system functions is based on the development of informatization, fully tapping the value of “information”, and providing “smart” services for dispatching, maintenance, and passengers. For example, the signal system intelligently adjusts the train operation density based on past passenger flow data and dynamic perception: if a certain device on the line fails, without the intervention of the dispatcher, the signal system generates a corresponding response based on the operation and failure conditions and combined with emergency strategies. The solution intelligently guides the troubleshooting of the fault and the restoration of the operation order, and based on the data of the platform, network and basic equipment, the cause of the fault can be quickly determined after the emergency braking of the train, without the need for subsequent analysis, etc.; if it is on the line When a major failure occurs in a certain area, the system can efficiently provide a cross-line or even cross-road network traffic relief program.


| Conclusion

Under the guidance of the “Outline for Building a Powerful Transportation Country,” urban rail transit, as a key link in the integrated development of the transportation system, needs to give full play to the advantages of independent technology, and emancipate the mind based on the accumulation of existing technologies; on the basis of ensuring safety, Advanced technologies, concepts and solutions in related fields are integrated with the urban rail signal system. It can be seen from its historical development law and the status quo of foreign industry development that the evolution of the blocking system and system architecture is an inevitable trend, and “smart urban rail” is gradually taking root. This requires the cooperation of owners and manufacturers and continuous innovation on the basis of inheritance. , In order to achieve the goal of “increasing efficiency, reducing costs and improving intelligence” of the urban rail signal system.

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