Research On Key Modules Of Communication Front-end Engine Of Subway SCADA System

With the development of smart transportation and smart city,the rail transit SCADA system is developing towards a distributed trend.The number of subsystems collected by the system increases,the communication protocol is diversified,and the communication links between nodes are complicated and highly coupled.Based on the above trends,this thesis studies the key modules of communication front-end engine(FEP)in distributed SCADA system,the data acquisition and data forwarding module.The main work has the following points:1.For the problem that the number of subsystems collected by the SCADA system is large and the communication protocol is different,a software module that can configure the specific communication parameters,load different communication protocols,and collect data of each subsystem is developed.The design of the data acquisition thread,the protocol processing thread and the IEC60870-5-104 communication protocol driver for power subsystem is discussed in detail.2.Based on the above characteristics of data acquisition thread and protocol processing thread decoupling,the thesis studies the lock-free circular queue algorithm using CAS-LOCK mechanism to synchronize between threads,and then combines the scenario of this article(single producer single consumer),simulated TCP enqueue and dequeue cases,analyzed and verified the three methods of completely unlock-free,CAS-LOCK,and mutex Mutex.The performance of CAS-LOCK is 20% higher than that of Mutex,and it is also objective.The problem of the algorithm is analyzed.3.Based on the requirement of data forwarding and synchronization between distributed FEPs,avoiding the bottleneck of high time and space coupling of traditional CS architecture or P2 P network,papter researched the data distribution mechanism of DDS,designed a content-centric publish/subscribe mechanism based on DDS component,completed the data structure mapping from data collection to DDS,designed a data transmission algorithm based on dead zone displacement and period between FEP nodes.The algorithm reduces the certain amount of transmission traffic in the network under the premise of ensuring the reliability of data communication,then the reliability QoS and deadline QoS in RTI-DDS are discussed to ensure real-time performance.4 Finally,the real-time and accuracy of the single FEP communication with multiple communication protocols and the DDS-based data distribution between multiple FEPs were tested.The time delay of data collection for the typical configuration of PSCADA and EMCS subsystems is within 1 s.In data forwarding,the time difference between the subscriber receiving the digital data and the publisher sending the data is within 100 ms.The system meets the accuracy and real-time performance indicators of the rail transit SCADA system after verifying.Based on the above work,the actual results of this thesis are as follows:(1)Research and design a unified framework of data acquisition modules,which can integrate subsystems of different communication protocols.(2)the data forwarding module is researched and designed using RTI-DDS components,which makes the system's scalability more enhanced.The innovation of this thesis are mainly as follows:(1)In the single-producer single-consumer scenario of the acquisition module,the CAS-LOCK mechanism is designed for synchronization between threads to improve performance.(2)The RTI-DDS component is used for the data forwarding module,and a data transmission method combining dead zone displacement and period is designed,which reduces the transmission traffic in the network,ensures the reliability of data communication.The system is currently in the research and development phase and will be used in new and old projects in the city subway in the future.