Analysis and implementation of IEC61850ft9 substation automation system configuration tool

　　IEC61850 is a configuration tool for substation automation systems, in which the Substation Configuration Description Language (SCL) is defined in the IEC61850-6 section. The SCL language is a specific, extensible identification language defined based on the syntax rules and structure definitions of XML and in combination with the needs of the IEC61850 standard. The SCL language is equivalent to a specific application of the XML language in the IEC61850-based substation system. XML is platform-independent, so the data in the file can be exchanged between engineering tools from different manufacturers and different platforms.

　　The introduction of SCL has the following two functions: one is to describe the functions and operating parameters of IED; the other is to describe the system. This paper mainly analyzes the configuration tool in the substation automation system based on IEC61850, and introduces the design method of the application of SCL system configuration tool .

　　1 SCL Document Structure

　　XML document includes three parts: DTD (Document Type Definition) file, XML file and style sheet. SCL language is based on XML. Similarly, SCL document also includes these three parts.

　　1.1 DTD file

　　DTD files define tags and their attributes to complete declaration and tagging tasks. The IEC61850-6 standard gives a detailed definition of the DTD file of the SCL language. In theory, tags and attributes can be defined arbitrarily within the standard as needed, but in practical applications, the definition of DTD is very difficult, including the availability, simplicity, and good data model abstracted from actual devices of tags, which all require rich practical work experience. All devices that support this standard will use the same DTD file.

　　1.2 XML File

　　This file uses tags defined in DTD files to complete the task of data object tagging, that is, to describe data objects such as IEDs and systems. XML files are strictly constrained by the definition of DTD. The IEC61850-6 standard does not specify functions or function allocation. The functions of each device are different, and the LNs configured on the IED are also different. Therefore, the content of the XML file is also different, but the IED has the ability to process XML files.

　　1.3 Style Sheet

　　A style sheet is a document that specifically describes the presentation of a structured document. From an application perspective, IEDs can directly process SCL data files and can operate normally and interact with the system as long as they obtain the required information. Therefore, style sheet files are generally not required by the system.

　　2 SCL Object Model

　　According to the substation architecture, SCL describes three object models: substation, communication and IED.

　　The substation model is mainly used to describe the functional structure of a substation and to identify the primary power equipment in the substation and the connection relationship between them.

　　The communication model is mainly used to describe the connection between logical nodes through the logical bus and the IED access point. The communication structure specifically includes the object model of the IED's mac address, IP address and subnet mask, as well as the client/server relationship between logical nodes and other information.

　　The IED model describes the model information of each IED, including report receivers, logical node instances, data object instances, etc.

　　3 SCL data exchange mode

　　3.1 SCL Information Flow Model

　　The communication and transmission of SCL files within the substation involves three concepts: system configuration tool, IED configuration tool, and IED database.

　　The system configuration tool is a tool that uses SCL to configure and manage substation automation systems. It can input and output SCL files defined in the IEC61850-6 standard.

　　The IED configuration tool is a special tool for IED debugging provided by the IED manufacturer. The tool can generate specific IED description files (SCL files with the suffix .ICD) and download them to the IED. It can also provide ICD files to the system configuration tool and process SCD files generated by the system configuration tool.

　　The IED database is divided into a parameter library and a real-time library. The parameter library is used to describe the substation model and communication model, while the real-time library is used to describe the IED model. The IED database includes various information data and attributes of the substation, which can be called by configuration tools and systems.

　　3.2 SCL information flow process

　　The SCL data flow model does not include DTD files. XML files are the files that actually contain configuration data and are also the main files involved in the flow of configuration data. Figure 1 shows the data exchange process of SCL documents in the entire system, which is the process of system management configuration.

　　The IED configuration tool can obtain the ICD file of each IED and send it to the system configuration tool. The ICD file only contains the basic information of the IED, and its related parameters (such as network parameters, etc.) are not set.

　　After receiving the ICD files of the entire station, the system configuration tool will analyze the information of each IED and obtain the information of each logical node and data object in combination with the IED database to generate or manually input configuration information, and at the same time generate the SCD file and return it to the IED configuration tool.

　　The IED configuration tool can receive and process the SCD file, and can generate a configuration file CID downloaded to a specific IED based on the configuration information of each IED obtained.

　　When the IED is started, the CID file is first parsed to obtain information, and the IED is initialized based on this information. For example, the network I/O will be configured and started according to the obtained network parameters.

　　When the IED is operating normally, it can communicate with the IEC61850 client to exchange data. The SCADA system can configure parameters according to the SCD file. When running in real time, it will generate a parameter library and a real-time database.

　　4 Design and implementation of SCL configuration tool

　　IEC61850 defines a hierarchical structure for the substation model, and the corresponding SCL also uses a hierarchical structure to describe the data model of the substation. Based on the hierarchical model of the SCL file, this program uses a grid data model to simulate and implement this data structure, and uses XML parsing technology based on SAX (Simple API for XML) to extract information from the SCL file. The data, attributes and their relationships at each level are displayed in a nested chart format. The human-computer interaction interface is friendly and can configure the SCL document. This program adopts a C/S architecture as a whole, which can support the reading and configuration of multiple IEDs. During the design, plug-in technology architecture can be used in some details (such as XML membrane blocks) to facilitate the use of mature software modules, which is more conducive to future maintenance and upgrades.

　　The development environment of this program is VC++6.0, which can adopt modular design scheme and COM-based component technology, and can use a large number of mature software and open program modules, so it can reduce the development cost and development cycle, and also facilitate software maintenance and upgrade. This design mainly consists of chart control module, XML parsing module, information library module, configuration interface module and communication module.

　　4.1 Configuration interface module

　　This program mainly provides a friendly visual user configuration interface to open the corresponding SCL files, such as the ICD format file of IED. Click the menu or button "Configuration" to open the user configuration interface, and click the corresponding property page to configure the network parameters, data sets, GOOSE and other system requirements of the IED. Figure 2 shows the basic parameter configuration interface of the IED named REF615.

　　4.2 XML parsing module

　　This program uses the JAVA version of Xerces-J1.4.4 parser, which is currently the most robust and powerful XML parser. It can ensure the efficiency, reliability and correctness of the program in processing SCL files. In addition, the cross-platform advantage of JAVA language is also very convenient for program maintenance, upgrading and transplantation. The XML parsing function of Xerces-J parser can support three XML parsing technologies based on DOM, SAX and JAXP. Considering the huge amount of data in IEC61850 substation, as well as the multi-level and complex associated data objects, rich and diverse functional constraints and attributes of the data, it is necessary to use an efficient and fault-tolerant parser. Based on SAX XML parsing technology, this design uses a stream method to read SCL files and parse them line by line and operate sequentially. Compared with DOM technology, this method occupies less resources, is fast and stable, and does not need to create objects for all nodes as in DOM. Therefore, this program uses the Xerces-J parser based on SAX technology. In addition, SAX adopts a "push" model for processing XML events, which does not require the SCL file to be loaded into memory at once, which allows the SAX parser to parse documents larger than the system memory, and the SAX "push" model can be used in a broadcast environment, and multiple ContentHandlers can be registered at the same time. It can receive events in parallel, instead of processing them one by one in a pipeline like DOM.

　　4.3 Database Module

　　The database module is mainly used to analyze and store various data information of the SCL file parsed by the XML module. The data object storage model can be implemented according to the definition of IEC61850-7, including a series of data models and object instances such as logical devices LD, logical nodes LN, basic information of common data classes CDC, associated services, and access interfaces.

　　4.4 Chart Control Module

　　For the hierarchical model, the most advanced programming technology is to use tree controls for control and display. This technology can intuitively display the relationship between levels, but it cannot intuitively display the relationship between data and attributes and functional constraints. The chart control model can intuitively and three-dimensionally display this relationship in the form of tables and graphic tags, and can also efficiently add, delete and modify SCL element nodes. This module can form a grid association model based on the data information obtained by the XML module and display it using the CrystalCell chart control; each layer can use a relatively independent table (each SCL file is a large table, and the data is nested in the corresponding cells of the large table) to display all its data elements, and can automatically determine the number of rows and columns according to the number of data elements and the number of data attributes. The data at the same level is displayed in rows at that level, and the attributes of the same data, such as type, functional constraints, reference marks, text descriptions, etc., are displayed in columns in the data row. In the corresponding places of the rows and columns, you can also add pictures, symbols, trigger controls or tables and other tags to annotate the function of the data element and the relationship between the data elements. The data attributes and data operations are clear and intuitive, and the data relationship is more three-dimensional.

　　4.5 Communication module

　　According to the information exchange process in this article, the configuration tool used must have real-time and reliable network transmission function. This module can realize the mapping from ACSI to MMS according to the definition of IEC61850-7 and IEC61850-8. The MMS package can use SISCO's MMS 5.06 version, which can transmit SCL files and IED real-time data at high speed and in real time, and is not restricted by specific IED communication protocols.

　　5 Conclusion

　　Compared with the traditional engineering configuration method, SCL has more prominent functions and advantages. Since IEDs are interoperable and interchangeable, the configuration is simple and error-prone, and the meaning of data objects is clear, it can greatly reduce the workload of engineering and reduce the difficulty of engineering integration of substation automation systems based on the IEC61850 standard.