Network RTU based on Embedded Linux

　　The distributed network remote terminal unit (RTU) shows its advantages over the traditional RTU in function, reliability and easy maintenance. This paper introduces a distributed network RTU based on Embedded Linux, which has powerful network communication function and good openness. RTU is not only a terminal device for data acquisition and control, but also can integrate many expansion modules and become the core platform of information processing in substation. Especially in the hierarchical voltage control system. As the primary voltage control, the local reactive power / voltage control module can be fully integrated into the network RTU. On the one hand, this mode is conducive to coordination with the secondary voltage control system, on the other hand, it is also convenient for maintenance and can effectively reduce the investment cost.

　　Because the network remote terminal unit RTU (remote terminal unit) has strong data processing ability and open architecture, it can be used as a core information processing platform of substation, and many extended functions can be realized on this platform, especially because the global voltage / reactive power control system has been gradually implemented in China, The reactive power / voltage control device in the substation exists as primary voltage control. Coordination with secondary voltage control is required. This paper expands the function of RTU, integrates reactive power and voltage control and other functions into RTU, and forms a comprehensive RTU with good cost performance. This system is based on Linux operating system platform.

　　1. Introduction to Linux operating system

　　Linux is an operating system similar to UNIX, based on micro kernel, fully memory protected, multitasking and multi process. Support a wide range of computer hardware, including x86, alpha, SPARC, MIPs, PPC, arm and NEG. Most of the existing processor chips such as Motorola. The program source code is all open. Anyone can modify and distribute it under the GNU General public license GPL (GNU General Public Licenses! E). So. Developers can customize the operating system; There is no need to worry about the threat of "back door" in the MS Windows operating system.

　　At the same time, due to the control of GPL. It ensures the mutual compatibility of the system. Linux also has a large number of developers, and the technology is developing rapidly. In addition, Linu is equipped with perfect development tools familiar to UNIX users, and almost all application software of UNIX system have been transplanted to Linux. Linux also provides powerful network function and graphical interface, and has a variety of optional window managers.

　　1.1 advantages of Linux

　　a. Compared with traditional DOS, Linux is powerful. Compared with windows series, Linux also has its own advantages, that is, stable system, good openness, strong tailoring and flexible configuration. The uClinux module based on ARM processor is about 5chdk. With RTU software module, the whole system can be stored on 2M chip; The RTU system installed on comnactpc only needs 32m memory card to realize Chinese graphical interface and a variety of network practical functions. Powerful Linux can also provide convenient remote graphic display, convenient maintenance and use.

　　b. Low cost. Linux is a free operating system. Anyone can download and use it freely on the network. Compared with expensive commercial operating systems such as Windows CE or VxWorks, the use of Linux greatly reduces the software cost of RTU devices.

　　c. Safe and reliable. At this stage, most RTU systems adopt micmsoftwindows platform, which generally has the disadvantages of weak security and vulnerable to virus. Generally, anti-virus software shall be installed when RTU is running. Even so, the effect is often unsatisfactory, and it also increases the maintenance workload of the system. This is a serious security problem for the interconnected network RTU. Linux inherits the advantages of traditional UNIX systems, while the number of viruses is very small and reliable. In addition. 1 by adjusting the relevant Linux kernel options or service configuration, it can effectively resist conventional attacks.

　　1.2 introduction to embedded Linux

　　Embedded system needs a set of operating system with high simplicity, friendly interface, reliable quality, wide application, easy development, multitasking and low price. Because of the openness of embedded Linux, it is very suitable for most Internet devices. Linux can support different devices and configurations. Embedded Linux has good portability and low cost. It can quickly become an operating system for various devices. Due to the use of embedded operating system, low configuration and relatively simple hardware can be used. Therefore, RTU developed with embedded operating system has the advantages of low energy consumption and high reliability. The embedded operating system adopted by RTU in this paper is a high-end embedded system, which requires many advanced functions, such as graphical user interface and network support.

　　2. Distributed network RTU

　　2.1 networking

　　Traditional RTU generally uses serial port to transmit data, and the communication speed is often the bottleneck restricting the performance of the system. After the network mode is adopted in this paper, the data transmission speed can reach 2Mbit / s, 10mbit / s and 100mbit / s to meet the requirements of telecontrol data transmission. At the same time. The functions that the network can provide (such as IP addressing) are far beyond that of serial port, which provides a way to realize the application of distributed system.

　　IEC TC57 puts forward a unified communication protocol system of power system, which divides the communication system of the whole power system into process bus (IEC61850), station bus (IEC61850), remote communication (iec60870-6 tase. 2 or IEC61850 +) and enterprise bus (iec61968uib), and Ethernet based on TCP / IP is adopted at the bottom layer. Using standard TCP / IP Ethernet interface can improve the interconnection of the system and provide convenience for future function expansion.

　　2.2 characteristics and composition of distributed ['u

　　2.2.1 characteristics of distributed RTU

　　The traditional centralized RTU takes analog quantity, digital quantity and pulse quantity as input respectively. The primary data of the power grid needs to be connected to the measurement and control device through a large number of secondary cables and transfer screens. The unit distributed RTU used in this paper directly faces the equipment for measurement and control. The embedded module can be installed on the primary equipment nearby, and only one network cable can be introduced. Its structure is shown in Figure 1.

　　Compared with centralized RTU, distributed RTU has the following advantages:

　　a. Cost reduction. The embedded measurement and control module shall be installed nearby, and a small number of simple network cables shall be used to replace the complicated secondary cables. It will greatly save substation space and reduce cost.

　　b. Convenient installation and commissioning. Distributed RTU is adopted to reduce the overall complexity and avoid many wiring errors and cumbersome debugging process. When the primary system of substation is expanded, only the corresponding measurement and control unit needs to be added. The database can be expanded without affecting the online monitoring　Normal operation of the system.

　　c. Reduce data flow and improve system reliability. For the traditional centralized RTU system. If the RTU host is paralyzed, the whole rritu will be paralyzed, while the distributed RTU does not have this problem: each distributed module is an independent module on the network and is not affected by other modules. They access the whole network through a local hub, which increases the flexibility of system hardware configuration.

　　d. Provide access and control between modules. Through the network, the mutual visits of various modules can be easily realized, so as to enhance the scalability of the system. Compared with centralized, network distributed system can.

　　There are many modes:

　　a. Mode 1 is Bay layer, network communication management layer and station level layer., If the master station does not support direct communication to the measurement and control unit, it can only use the substation as the unit to process data. This mode can be adopted, that is, specify or add a module as the communication hub to communicate between the master station and the measurement and control module on the Bay layer. The station level is the local monitoring or relay protection engineer station.

　　b. Mode 2 is the Bay layer and the network communication management layer. As above, for unattended stations, local monitoring is not required. There is no need to implement the local monitoring function on the repeater.

　　c. Mode 3 is the compartment layer. The master station communicates directly with the distributed module of the substation. Suitable for unattended substation, this mode needs the support of the master station. Lowest cost. It fully embodies the advantages of distributed and modularization.

　　2.2.2 Embedded Measurement and control module

　　The distributed system of a substation is composed of more than ten or even dozens of measurement and control units for primary and secondary equipment. The hardware adopts the industrial acquisition module based on ARM processor, and the operating system is a variant of Linux: uClinux. The storage space occupied by the whole module is less than 2m. The measurement and control module includes functions for all measurement and control equipment. For specific applications, just provide different configuration files.

　　2.2.3 communication management module

　　As mentioned above, since most main stations can only communicate with substations, a module in the station is needed as the communication hub. It mainly completes the collection and summary of data and the forwarding function to the dispatching and centralized control station. At the same time, it also receives the control information from the superior and sends it to each module for corresponding control. The adaptability of software and hardware platform is guaranteed to the greatest extent. As the core program of communication, its efficiency and stability are very important. Under Linux, the network interface based on streaming TCP protocol can be adopted, and the operation efficiency of the program can be greatly improved through the select mode similar to interrupt.

　　2.3 RTU expansion module

　　With the development of computer hardware, CPU, memory and other resources on RTU host no longer become the constraints affecting RTU performance. At the same time, Linux operating system also provides advanced memory management and multitasking support. The traditional local monitoring, protection and maintenance and local reactive power and voltage control functions can be added to the RTU host, such as real-time data display, alarm, printing and historical data storage on the primary wiring diagram, which greatly reduces the complexity and cost of the system. The RTU system in this paper is to put each module and communication management module on a high-performance industrial computer or compactpc.

　　2.3.1 voltage and reactive power integrated control module traditional substation

　　VQC (voltage and reactive power (q) contr) device is an independent device with complete software and hardware. It needs to collect the reactive power of transformer, bus voltage and main switch position for analysis and decision-making. In addition, the issuance of control command also needs an independent control unit. In fact, RTU has all state variables and control loops required by VQC; Especially in many places, VQC is not an independent terminal equipment, but a primary voltage control terminal that needs to be coordinated with the secondary voltage control software system. Distributed RTU and control center have strong communication ability and open architecture, so integrating VQC module into RTU can reduce the cost on the one hand, and more importantly, VQC control module can easily realize communication and coordination with control center. The RTU system proposed in this paper uses open real-time database technology, and other expansion modules can easily obtain various real-time data on RTU. At the same time, the function of VQC can be realized by using relevant logic operation and control interface.

　　2.3.2 local monitoring module

　　With the emergence of a large number of unattended substations, the importance of local monitoring is decreasing day by day. However, in terms of the current automation level of China's power system, it is necessary to provide a convenient and fully functional local monitoring module in 220kV substation. It mainly realizes the primary wiring diagram and its real-time data display, as well as the configuration and query of the system. Whether in the system commissioning stage. Or in the process of system adjustment and upgrading. Local monitoring modules will play an important role. For small and medium-sized substations. Its local monitoring module can be fully integrated into the communication management module of distributed RTU.

　　2.3.3 protection setting module

　　The virtual terminal provided by the communication management module can access the lower level equipment, indirectly query and set the relevant information of the protection equipment. The protection setting module is now implemented based on QT / Linux embedded / X11 / mswindows. As long as this module is installed on the computer of the network node, the protected data can be queried and modified online. It greatly facilitates relay protection and maintenance.

　　2.3.4 remote maintenance

　　The traditional RTU remote maintenance module is usually an independent complex module, which needs separate software and hardware support. Linux has powerful network functions and can easily make use of the various functions provided by the operating system

　　Network tools for remote maintenance:

　　a. Log in to RTU host by telnet / SS in text mode in centralized control station or dispatching center for maintenance:

　　b. Using XWindow software (EXT, exceeded, xwin32) on windows to log in graphically, which greatly facilitates the routine maintenance;

　　c. Use FTP to transfer data files and system configuration files.