Research on Data Transmission and Information Integration Technology in the Distributed Wind Farm SCADA System

Transcription

1 Applied Mechanics and Materials Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland Research on Data Transmission and Information Integration Technology in the Distributed Wind Farm SCADA System Yanfeng Tian 1,a, He Li 1,b, Zuoxia Xing 1,c,Gang Wang 2,d 1 Shenyang University of Technology, Shenyang, Liaoning, , China 2 State Grid Liaoning Electric Power Company Electric Power Research Institute, Shenyang, Liaoning, , China a y_tian@163.com, b lihe @163.com, c xingzuox@163.com, d wgang @163.com Keywords: SCADA system; power generation; wireless network; integration technology. Abstract. Distributed power is a new form of power generation, which under a limited transmission grid resources condition can makes full use of small resource. Therefore, it has economic and practical value to develop distributed farm. However, the SCADA system of distributed farm is the basic safeguard to ensure distributed farm to be safe, reliable and economical operation. Compared to other SCADA system, the SCADA system of distributed farm has difficulties in data transmission and information integration. This paper puts forward information integration technology based on OPC XML and data transmission technology based on the combination of ZigBee and 3G wireless network to solve the above problems. Introduction Distributed farms have the following features: the installed capacity of a single farm is small; farm is scattered; the power can access to local electric power grid by low grade voltage; the power can be exhausted within the scope of the local and don't need transmit over a long distance. These features make distributed power be very economic and give a big contribution in small field. Compared with other SCADA systems, the SCADA system of distributed farm exists the following technical difficulties: 1)monitoring system information integration problems, there are two reasons: on the one hand, as many as dozens of s manufacturers at home and abroad have different control technology and communication protocols that are generally incompatible, so that s monitoring system run independently and have difficulties to communicate with other remote SCADA system; on the other hand, different s manufacturers have different data format specification, so that different manufacturers local SCADA have difficulties in sharing, integrating and interacting information with the remote SCADA system;2)data transmission problem, also includes two aspects: on the one hand, in distributed farms, s have generally wide distribution area and big quantity, so it is difficult for s to communicate with short-range local SCADA system; on the other hand, due to the poor construction of farms communications equipment and the system requirements of real-time data transmission, high reliability and safety, the local SCADA system data communication with the remote system is difficult. According to the above problems, this paper proposes OPC XML information integration technology to solve the information integration problems of SACAD system in distributed farm and ZigBee combined with 3G wireless network data transmission technology to solve the data transmission problems of SCADA system in distributed farm. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (# , Pennsylvania State University, University Park, USA-18/09/16,12:18:54)

2 2642 Vehicle, Mechatronics and Information Technologies II System framework design This system design focuses on implementing SCADA system information integration and data transmission. In the design, OPC DA of each farm site access to s PLC data by ZigBee wireless network. On the one hand, the data of OPC DA is transmitted to local SCADA system, on the other hand, is transmitted to the by DCOM interface. Remote SCADA system uses B/S architecture. Through the 3G wireless network, remote SCADA system gets the data from the of each farm. The as the system intermediary, downward, is responsible for reading the real-time data from the OPC DA and storing data in the database of the local monitoring and control system. Upward, it provides Web services for remote SCADA system. System architecture is shown in figure 1. remote SCADA system 3 G communication network 3G communication module 3G communication module 3G communication module Local SCADA system OPC DA data base Local SCADA system OPC DA data base Local SCADA system OPC DA data base Wind farm Ⅰ Wind farm Ⅱ Wind farm N Figure 1 The diagram of farm SCADA system architecture Information integration technology based on OPC XML This paper proposes the OPC XML technology to realize the information integration of s monitoring system. OPC XML technology contains OPC technology and technology based on web service. The OPC technology solves the problem of communication between SCADA system with s PLC. The technology based on web service solves the problem of data format unification and realizes Internet application invoking data from local system. The technology based on web service, that combines OPC technology with XML technology, is well suitable for B/S(Web browser/ Web / database ) mode of SCADA system[4,5], in which web service serves as the middle layer of monitoring system. Information integration technology based on OPC XML in the application of distributed farm SCADA system Distributed farm SCADA system adopts B/S program mode. The web layer is principal made up of, which is in the middle layer of the entire system and responsible for the data conversion and transmission for the upper and lower layers, so the is the core to realize the information integration. It primarily implements the following two functions: firstly, it is responsible for the real-time data read from the OPC DA, storing the data in the database and completing the XML description and encapsulation of the real-time data; secondly, it serves as an XML web service to provide web services for the application layer users, which unifies data to XML format and then issues out XML documents to the remote SCADA system through binding hypertext

3 Applied Mechanics and Materials Vols transfer protocol or others. Data layer includes various s PLC and OPC DA. The Web client layer is remote SCADA system, is the Web browser connected to the Internet. The Web browser communicates with the by HTTP, TCP/IP protocol. Remote SCADA system has realized to access remote farm data and instantaneity monitor farms through standard web Browser. The consists of three parts: OPC client, OPC XML transformation, XML web service. Firstly, OPC client obtain the status information and real-time data of s from the OPC DA ; secondly, data is converted to OPC XML; finally, XML Web service releases data to the remote SCADA system. The OPC client defines the data information transmission and access methods between the and OPC DA. XML and OPC protocol conversion service mainly complete type conversion and data definition between XML protocol documents with the OPC interface specification. At the same time, it need complete parsing, splitting and assembling between the XML documents with the OPC data format, according to communication protocol. XML web service releases XML documents to the remote SCADA system, by binding to HTTP protocol or other FTP. Software development and design There are a lot of component-based tools to develop OPC DA, so developers need not know the details of the OPC specification and can relatively easily develop OPC DA. Therefore, in this article, we do not introduce how to develop OPC DA in detail. We will mainly introduce OPC XML DA software design process. The process of operation is as shown in figure 2. Start the OPC XMLDA applications Main process into the listening state Receive the request Start the data processing threads Parse the SOAP message call the corresponding OPC XML Service implementationmodule Access to relevant data by OPC DA Make the data packaged into standard SOAP messages back to the remote SCADA system Figure 2 The operation process of the In this paper, the operation process of the is as follows: after the user starts OPC XML program and finishes the system configuration of the, system starts up process monitoring module, to monitoring the HTTP port; when listening to the access request of remote SCADA, starts the XML data processing module threads, in which the receiving SOAP messages are resolved,the analysis and package of SOAP message in the module are accomplished by

4 2644 Vehicle, Mechatronics and Information Technologies II ASP.NET, so we need not write programs. Then the OPC data access module threads is started up, to read data from OPC DA through the COM/DCOM communications protocol of the OPC interface specification.the process of interaction between OPC DA client and is as follows: creating object and connecting to it; adding group and item; reading and writing data. Firstly, we create a COM object by CISID that is generated by the registration list of Operating System when OPC DA client service is installed installation. Once the COM object is created, OPC DA client will get an IOPC SERVER interface.then, we utilizes IOPC SERVER interface to create OPC DA group. Finally, we read data by the interface functions that are called by IOPC SERVER interface pointer.finally, after data is correctly resolved and stored in the specified database and high-speed buffer, it is transmitted to remote SCADA system by the format of SOAP message. The data transmission technology based on the combination of ZigBee and 3G wireless network The data transmission of distributed farms can be divided into two levels: the first level is the short-range data transmission, in which data transmit between each s with local monitoring center; the second level is remote data transmission, namely the data transmission between local monitoring center with remote monitoring center. The s of distributed farm are scattered, and the capacity is small. If the short-range data transmission use cable communication mode, such as optical fibers, the construction difficulty will become larger and cost will be high. For remote data transmission, the infrastructure of cable communications equipment is weak in distributed farm. However, monitoring and control system itself puts forward strict requirements on the real-time and security of data transmission. To solve above problems, our system use ZigBee wireless network technology to realize short-range data transmission, and 3G wireless network technology to complete remote data transmission in the distributed farm SCADA system. The short-range data transmission technology in the distributed farm SCADA system ZigBee wireless network technology uses IEEE protocol. The wireless network, in which information is with the method of automatic routing, supports for AES-128 encryption. And the wireless network has short communication delay time and dormancy activation delay time. These characteristics can result in better performance in reliability, security, real-time and network topology. ZigBee wireless network is composed of ZigBee and the network. ZigBee is also known as network nodes, that includes sensor nodes and routing nodes. Sensor nodes connect to data acquisition equipment, such as PLC and sensors. And routing nodes serve as a transfer station, by which you can transfer information from other network nodes. When the distance between s PLC and the monitoring center is outside the ZigBee coverage, we can extend it by adding the network s routing nodes[7,8]. It is worth mentioning that ZigBee wireless network can Self networking and multichannelly communicate, so the different nodes can automatically search for each other and produce a connected network in their communication range. The above feature of ZigBee wireless network makes adding or deleteing new s hardly affect the original s communication with the monitoring center in distributed farms [9]. In the paper, the structure diagram of short-range data transmission system is as shown in figure 4. The ZigBee nodes (network nodes) are composed of CC2530 ZigBee wireless transceiver module and wireless signal amplification module. We adopt simulated RF front-end chip TM2006 as the wireless signal amplification module in this paper. The use of the wireless signal amplification module is to enlarge the communication range and ensure real-time transmission. Whatever its topological relationship is, ZigBee wireless network only has a network that is the command center of the whole network and needs to choice network frequency channel, set up network node, manage data security, collect data and so on. Its hardware are composed of control processor (MCU), ZigBee (wireless transceiver module and wireless signal amplification

5 Applied Mechanics and Materials Vols module), and other auxiliary hardware. The S3C2410 chip, produced by Samsung Company is used as the control chip (MCU). The process of the short-range transmission between s and control center is as follow: firstly the data of s transmits to s; then s communicate with the OPC DA via a serial port; finally control center calls the data of control center. Wind Wind Wind Local monitoring center Annotation: Wind Routing nodes Sensor nodes Wind Figure 4 Distributed short-range data transmission Remote data transmission technology in the distributed farm SCADA system In this paper, the 3G wireless network communication technology is used to realize remote data transmission. In order to ensure the requirements of real-time, reliability, and security of data transmission in remote SCADA system, 3G data communication network adopts 3G VPDN model. Specific implementation is as follows: (1) Adopt proprietary APN + binding access authentication in the range from the 3G routing of local monitoring center to operators LAC. When 3G wireless access to the deployment of the system, it first apply to the operators for allocating APN private network, which is similar to proprietary local 3G wireless network, and ensure that 3G network nodes only access to our private 3G network and are unable to communicate with other networks. Network nodes access to 3G wireless network by 3G router. Terminal users account and password, and network users IMSI information, which is composed of 15 unique digits and puts in the SIM card, Operators will make network user (IMSI is uniquely identified in operator network mobile user number, is composed of 15 digits, put in the SIM card), is previously configured in the operator's identification. When network nodes 3G router apply to connecting 3G wireless network, the user whose binding information and password can successfully pass certification, can access to our 3G private network. By the means, we can prevent illegal 3G SIM card users from entering 3G private network [10]. (2) Adopt L2TP VPN private tunnel (VPDN virtual private dial-up Internet) in the range from operator LAC to remote monitoring center router. In order to ensure the privacy of data transmission, users apply to mobile communication operators for enterprise group users 3G VPDN. 3G VPDN uses safe L2TP tunnel transfer protocol and builds a virtual undisturbed dedicated channelon based on existing dial-up network. The structure of 3G VPDN wireless network is shown in figuer5.

6 2646 Vehicle, Mechatronics and Information Technologies II LAC AAA Server Server 3G Communication Module Proprietary APN + Binding Access Authentication Operator LAC IP Core Network L2TP VPN Private Tunnel Remote Monitoring Center The Monitoring Center Router Figure 5 The structure of 3G wireless network Conclusions In this paper, the SCADA system of distributed farm adopts the OPC XML technology to realize the information integration of different manufacturer monitoring and control system. The OPC XML information integration technology, putted forward in this paper, has solved the problems of communication, information sharing, integration and interaction with remote SCADA system. By combining ZigBee and 3G wireless network technology, a new communication technology is putted forward in the system, complementing ZigBee and 3G wireless network technology. The method solves the difficulties of short-range data transmission between s with local SCADA system, and remote data transmission between local SCADA system with remote SCADA system. Acknowledgement This work is support by state grid technology project (Research on the Access Technology and Engineering Demonstration of Distributed Wind Power) Grant# DKYKJ [2012]001-1 References [1] Guowei Zhang, Guangcai Gong and Zhi Wu: The status and prospects of power utilization [J], Energy saving equipment, 2007(01):71-76.In Chinese [2] Qiying Hu:The development prediction of power prediction[j], Renewable energy sources, 2005(06): In Chinese [3] The European energy association. Edit by greenpeace international. On power reaches 12% of the world's electricity in 2020,Beijing, China environment science press, 2004, In Chinese [4] Haidong Wan, Boyu Qi and Yijun Xia: Wind farm SCADA system design [J], The Modern Electronic Technology, 2010 (312) : In Chinese [5] BTM Consult Global Wind Energy Council, [6] Weichun Huang, Hongbo Su: Research on OPC XML-DA in the application of fieldbus remote monitoring system [J]. Microcomputer information, 2007, 23 (6-1). In Chinese [7] Garrad Hassan, Partners Ltd and Glasgow:SCADA in farms[j], Instrumentation in the Electrical Supply Industry, 1993, 11(1): [8] Brent Brobak, Lawrence Jones: SCADA Systems for Large Wind Farms[J], Grid Integration and Market Requirements, 2001, 26(2): [9] Ziyi Liang, Zhenghua Ma: Research on farm remote monitoring and control system based on ZigBee and GPRS [J], Computer and digital engineering, 2010, 11(2): In Chinese [10] Feng Lin: Dignosability of Discrete Event Systems and Its Applications[J], Discrete Event Dynamics Systems, 1994, 12(2):