Raylı sistemlerde sanal blok sinyalizasyonu
Virtual block signalling in railway systems
Yazar: DOĞANCAN DÜNDAR
Danışman: PROF. DR. SALMAN KURTULAN
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Raylı Sistemler Ana Bilim Dalı / Raylı Sistemler Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2022
Konu: Bilgisayar Mühendisliği Bilimleri-Bilgisayar ve Kontrol = Computer Engineering and Computer Science and Control ; Elektrik ve Elektronik Mühendisliği = Electrical and Electronics Engineering
Dizin: Blok zinciri sistemi = Blockchain system ; Raylı sistemler = Railway systems ; Sinyalizasyon = Signalization

Özet:
Raylı sistemler hayatımızda her geçen gün daha fazla önem kazanan bir ulaşım türü olup, teknolojide yaşanan gelişmelerle de kendini sürekli yenileyen bir yapıya sahiptir. Bu bakımdan raylı sistemler artan şehir nüfusuna cevap verecek şekilde geliştirilmiş, aynı zamanda da güvenlik kavramlarından ödün verilmemiştir. Bütün bunların gerçekleşmesini sağlayan sinyalizasyon sistemleri, güvenlik ve işletme açısından en önemli rolleri üstlenmektedir. Sinyalizasyon sistemleri ayrıca tüm dünyada sürücülü işletmelerden, sürücüsüz otomatik tren işletmelerine geçişi sağlamıştır. Otomatikleştirilen demiryolu işletmeleri, hem personel maliyetini azaltmış hem de sistemde insan kaynaklı hataları minimize etmiştir.
Raylı sistemlerin ilk sinyalizasyon örneklerinden olan sabit blok sinyalizasyonunun artan talebe cevap vermekte zorlandığı noktalarda, haberleşme sistemlerinde yaşanan ilerlemeler, birtakım yapısal sorunları çözmede başarılı olmuştur. Tren ile hatboyu arasındaki kablosuz iletişimin daha güçlü ve güvenilir hale gelmesi, hatboyu üzerindeki yükü hafifletmiş, böylece ray devresi gibi tren meşguliyetini algılayan ekipmanların elimine edilmesine yardımcı olmuştur. Araçüstü donanımına eklenen odometri ve işlemci birimleri sayesinde trenler kendi konumlarını hatboyuna raporlayabilir hale gelmiştir. İletişim tabanlı tren kontrol sistemleri (Communication Based Train Control, CBTC) sayesinde işletme sıklığının artırılması, dolayısıyla kapasite artışı olağan hale gelmiş, artan şehir yüküne demiryollarının cevap verebilir hale gelmesi sağlanmıştır. Bu sayede CBTC sistemleri her geçen gün dünyanın onlarca şehrinde ve daha fazla projede kullanılagelir olmuştur. Benzer gelişmeler otomatik tren kontrol (Automatic Train Control, ATC) sistemlerinde de yaşanmıştır. Sabit blok sinyalizasyonunda kullanılan belirli ve değişmeyen uzunluklardaki blok mantığı, yerini yazılımsal olarak değiştirilebilir, fiziki olmayan sanal bloklara bırakmıştır. Buna göre bir ray devresi uzunluğundaki hat bloğu, sanal olarak tanımlanmış birden fazla hat bloğuna dönüştürülebilir. Hat bloğu uzunlukları azaldığı için trenlerin birbirine daha yakın seyretmesi mümkün hale gelmektedir. Ayrıca bu blok uzunluklarının değiştirilebilir olması sistem mimarisine esneklik kazandırmakta, projenin hatboyu ekipman maliyeti yükünü azaltmakta, kapasite artırımına olanak sağlamaktadır. Ek olarak tüm sistem alt birimlerinde kolayca değiştirilebilir modüler ekipmanlar kullanılması sistemin yedekli ve kolayca test edilebilir olmasını sağlamıştır. Bakım ve hata bulma süreçleri daha rahat sürdürülmektedir. Bu tez çalışmasında, CBTC öncesi sinyalizasyon türlerinden bazıları ele alınmış, ardından CBTC sistemlerinin ayrıntılı anlatımı verilmiştir. Sinyalizasyon sisteminin omurgasını oluşturan bu iletişim altyapısının temellerine değinilmiş ve ana fonksiyonları ile birlikte çalışma mantığı açıklanmıştır. Ardından hat bloklarını
sanallaştırma yöntemlerine geçilmiştir. Sanal blok sinyalizasyonunun bir CBTC altyapısı üzerinden nasıl gerçekleştirildiği açıklanmış, araçüstü ve hatboyunda kullanılan ekipmanlara ve anklaşman sisteminin detaylarına dair bilgiler verilmiştir. Tren ile hatboyu arasında kullanılan veriler listelenmiş, bu verilerin anklaşman yazılımı içerisinde nasıl kullanıldığı açıklanmıştır. Ardından anklaşman yazılımının mimarisi üzerinde durulmuş, alt fonksiyonların görevleri anlatılmıştır. SIEMENS TIA Portal üzerinden ladder ve GRAPH dili ile kodlanan hatboyu ATC yazılımının içeriği paylaşılmıştır. Yine programlanabilir lojik kontrolör (Programmable Logic Controller, PLC) Simülatörü ile, hareket yetkisi paketlerinin nasıl üretildiği gösterilmiştir. Simülasyon üzerinden çeşitli senaryolar altında hareket yetkisi mesajının davranışları incelenmiştir. Ardından sinyalizasyon sistemlerine dair dünyadaki diğer önemli yöntemlere değinilmiş, son bölümde ise sonuç ve öneri görüşleri sunulmuştur.

Abstract:
Railway systems have increasing importance in our lives. Thanks to the advances in several technological areas, railway industry is also developed according to the needs of the sector, with always taking safety concerns into consideration. To realize these requirements, signalization systems are developed continuously and have the most significant roles in the overall system. Without signalization systems, it would not be possible to have such low headway times and greater capacities in railway projects, while maintaining safe train operation. Interlocking software and automatic train control systems together construct powerful signalization systems which makes our transportation system faster and reliable. Advanced railway signalling systems also make driverless train operation possible while minimizing the personnel cost and human driven hazard probabilities. Improvements on communication systems help engineers to solve some structural problems of the railway signalling, when fixed block signalling system fails to respond the requests from the users. With the more robust and secure wireless communication between onboard and wayside systems, wayside system's workload is lightened so the need for physical equipment to capture train occupation, such as track circuits, could
be eliminated. Thanks to the odometry and processor units which are installed to the train, onboard system can report its location information continuously to the wayside system. Thus the positions of the all trains in the system shall be known by the region automatic train control system with high granularity. Communication Based Train Control (CBTC) systems allow headway times to be reduced and line capacity to be increased, so that railway system can deliver high quality service to its users. Accordingly, more railway projects in several cities are designed and commissioned
with CBTC signalling systems. Similar improvements took place also on Automatic Train Control (ATC) systems. Block lengths which are limited and fixed to track circuit design and cabling, shall be turned into virtual blocks which are not physical but adjustable by the software easily. Consequently, a fixed length track block can be divided into the several virtually defined blocks, where its number may vary according to the project requirements. Because of the shorter block lengths, trains can follow each other closely. In addition, changeable block lengths provide resilience to the system architecture, lower the cost of wayside equipments and allow capacity increment. CBTC system consist of
replaceable unitary equipments, which makes the overall system modular, redundant and easily testable. Moreover, maintenance and troubleshooting processes are simpler. In this thesis, some pre-CBTC systems are introduced briefly before CBTC systems are examined in detail. System architecture and working principles of this backbone of the communications system are given with its sub systems and functionalities. Then, the virtual block signalling principles, the methods of virtualization of blocks and how it is built onto CBTC system, are detailed. Onboard and wayside equipments are shown with diagrams and interlocking software details are given. The messages between onboard and wayside systems are listed and how they were used in interlocking software are explained. The architecture of wayside ATC software and its sub components are elaborated. Wayside ATC software is written with SIEMENS TIA Portal's ladder and GRAPH methods. In addition, movement authority message is produced and simulated in different scenarios by Programmable Logic Controller (PLC) Simulator. Lastly, the other signaling method such as dynamic block signalling and future concept of virtual coupling are introduced. Results and suggestions are given as a final chapter. To elaborate CBTC network and its working principles, it is divided into three parts where wayside network system, onboard network system and data transmission system are detailed separately. Wayside network, which consists of equipments that are installed on the line, such as radiax cables, line of sight antennas and access points, are shown with their architecture. Redundant structure of access point loops and base radio frequency scheme is given with their diagrams, where onboard equipment benefit to stay connected in case of a failure. Communication initiation between wayside and onboard networks are also shown. Onboard network which comprises antennas, radio modules and switches works to relay vital information produced by onboard ATC system and receive wayside ATC system commands. Data transmission system details are also given by showing network architecture which are interconnected by fiber optic backbone. Communication interfaces of these systems are showed with example generic packet contents. Block virtualization notion is examined in detail with literature research on this concept. Virtualization allows to reduce safe train separation distance by shortening the long physical blocks which are fixed in installation phase. These track circuit blocks become shorter virtual blocks which is used again to separate different trains on the line. However, this time, trains may follow each other closer than before, while
eliminating waste of long block section behind the preceding train. Thus, the movement authority of the following train may extend to the end point of a preceding train's virtual block occupation. This is useful when the train traffic is dense, such as metro lines. Block virtualization needs new concept clarifications such as position information
production, real occupancy, virtual occupancy, speed profile and odometry parameters. Main onboard tasks are given with examples because onboard systems become smarter in virtual block system. Odometry parameters received from tachometers and Doppler radars, are sent to onboard ATC where they will be processed. These redundant vital computers then produce the train position data by its processors. Thanks to communication system infrastructure, onboard ATC periodically reports its position values to the wayside ATC. The speed data is also used for constructing speed profile and calculation of braking distance. The line parameters such as block length, grade and curve value of a line section is stored in a memory of onboard ATC system. In this thesis, the focus is on wayside ATC software because movement authority, which is produced by wayside ATC, will be simulated for different scenarios. Thus, wayside ATC software components are examined to show their working principles and functions. Components, which each controlling different parts of the wayside system, are coded in TIA Portal with ladder and GRAPH methods. Movement authority message is one of the most critical packets of the system, which enables the automatic train operation. This message is produced by the wayside ATC system, using the data received from each train and the latest status of the wayside equipments. Route and point status, virtual block status and their corresponding speeds are some elements which effect the movement authority message limit. Flow charts are also given to show how the wayside components work. Movement authority simulation is done with TIA Portal Simulator, which allows to observe the bit and byte values of received and sent message packets. Movement authority message is relayed to onboard ATC and it contains the data pertaining to the block numbers to be proceeded and block speeds to be followed by train. A section of line is chosen as a test line to be coded to wayside software and this line contains a number of virtual blocks. These five virtual blocks of test line are enough to produce
movement authority message and observe its behavior in different circumstances and scenarios. According to the train location reports, wayside system derives the occupancy of the virtual blocks and uses this information to safe train separation. When the route is set in front of a train and the other conditions are met, a movement authority message is created so that train have authorization to move. The update of movement authority message is expected when the train moves in its route. This change in the message is shown in the simulation according the the train movement. It is also possible that movement authority message limit shall be shortened because of an equipment failure or unintended train entrance to the route. In these scenarios, it is shown that authority limit is reduced to the safest status. When the restriction removed, authority limit may extend according to the current conditions. To develop the virtual block concept further, the more advanced method called dynamic block systems can be examined. Moving block, in other words, also uses virtual block notion in its operation. However, in moving block, two trains may exist in the same virtual block. Safe train separation is done in more sensitive and accurate ways. This allows operators to move the trains with reduced headways and use the line with higher capacity. Another innovative method of train operation is called virtual
coupling. In this method, two consecutive trains are moving with less safe distance between them. This method assumes that preceding train will not stop suddenly, so the following train can trace it as if they are automobiles in the highways. Inter train links are required to form the train swarm, with the master train to lead the others. Block virtualization and other improved methods built onto this concept, are made possible with the developments on communication solutions, such as wireless communications. With CBTC, wayside and onboard systems are able to exchange
the higher amount of data which is needed to move trains safely on the line with the capacity increase. Instead of open lines with less train traffic, virtualization of physical blocks are feasible for the lines with greater demand of passengers, such as suburban and metro lines. Virtual block lengths can be several tens of meters in some scenarios, so it gives an opportunity to design some line sections with higher granularity. 90 seconds headway is the international goal in metro lines to deliver a service in high quality, without compromising safety concerns. Railway signalization
technology will be developed further to answer end user requests in the future for faster and safer travel, all around the world.