Design of One chip Communication Stack Processor and MMS Communication Stack Library Based on IEC 61850 Eunkyu In, Jongju Park, Sangwoo Ahn, Cheoljon Jang, Jongwha Chong Department of Electrical and Computer Engineering Hanyang University, Seoul, Korea
[email protected] Abstract—This paper deals with implementation of a MMS Communication stack library used in the processor and an IEC 61850 one chip communication stack processor of an IED used in a SAS server and a client. According to the definitions of IEC 61850 standards, communication services of SAS are divided mainly into three steps: initialization, processing and communication step. The three steps above defined in IEC 61850 standards are designed by using object-oriented programing language;C++. By using the IEC 61850 one chip communication stack processor, the processor makes it easy to manage and repair an IED, and supports compatibility between IEDs of different manufacturers. By using the IEC 61850 MMS communication stack library, not only user’s development hours are reduced but also it contributes to the automation of substation.
II.
SUSTATION AUTOMATION SYSTEM
Substation Automation System(SAS)[3] is a system to put the main electrical data into a database for operating, managing and monitoring the conditions of substation. Fig. 1 shows the major communication services and the path in the SAS which is modeling of substation by using the IEC 61850 communication stack library.
Keywords-IEC61850; IED; communication stack processor; communication stack library; SCL; MMS mapping;OSI 7 layers, oriented-object; ASN.1
I.
INTRODUCTION
In the latest substation system, to minimize human intervention, IT technology is mixed up with existing substation with automation and remote monitoring. It became possible by substituting established electronic devices to IED(Intelligent Electronic Device)[1] based on microprocessor with communication functions. Before the standardization process for inter IED communication service, IED manufacturers had manufactured IED with various types of protocol and provided them. However, IEDs for each manufacturer needed an additional device(i.e. wrapper) in order for inter-equipment compatibility due to the different protocol, and this attributed the rise to an additional cost of substation automation system. Therefore, IEC defined IEC 61850 standards[2] based on UCA2.0 and experience in Europe.
Figure 1. hGGG
IEC 61850 standards is defined as the system requirements in terms of the communication between IEDs within substation.
The SAS categorized into three network levels: system network, station bus, and process bus.
“This research was supported by the MKE(The Ministry of Knowledge Economy), Korea, under the KEIT(Korea Electrical Industry Technology research association).
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x
Monitoring system Interface) device. x
IV.
System Network: with
HMI(Human
Machine
Station Bus: Sending command / data message from HMI. Sending command / data message from each IED.
x
Process Bus:
PROPOSED ONE CHIP SOLUTION
The proposed one chip solution is combined with a logic processor and an IEC 61850 processor. Fig. 3 shows structure of proposed one chip solution. Functions of each processor are same with Fig. 2. One chip solution brings low cost, low power consumption, minimization, and high reliability. IED developers have the effect of shortening the development period of IED.
Periodic data collection for sampling analog and digital I/O value(electrical data). Real-time data transmission for command messages. IEC 61850 communication stack library in SAS applies to IEDs and HMI, and is defined on the system requirements related to the communication system between IEDs in SAS. III.
EXISTING IED STRUCTURE
H/W Architecture in existing IED consists of measurement control, digital I/O control, HMI control, and IEC 61850 server. Fig. 2 shows structure of a general IED based on IEC 61850.
Figure 3. An architecture of proposed IED
In Fig. 4, the proposed one chip has a main processor designed by VLSI for controlling peripheral device and combines a logic processor and an IEC 61850 processor. Proposed one chip solution is not like dual processor in PC, it works with independent processor module. The independent dual processor makes data processing and transmission faster regardless of operation of each processor in IEC 61850 communication circumstances. Also by removing duplicate line and bus, it achieves low power in IED, high efficiency and high reliability.
Figure 2. An architecture of general IED
Measurement control samples actual voltage and current value in digital value by the CT/PT processor module. In a case of odd value, the main processor module activates digital I/O control part and performs actual IED’s function as circuit breaker. Measured values and operation status of an IED can be shown by the HMI processor module. An IEC 61850 server consists of an IEC 61850 processor module for operating in functions of IEC 61850 communication stack library and communication module for communicating with other device(e.g. IED).
Figure 4. A structure of proposed one chip
Fig. 5 and TABLE I are layout and specification for one chip IEC 61850 communication stack processor. Its size is 5cm ㄐ5cm.
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TABLE I.
IEC 61850 SOC SPECIFICATION
IEC 61850 SoC Spec. Two ARM926EJ-S core @333Mhz 128Kbyte internal memory 32Kbyte Rom 8 channels DMA EBI Interface for Gigabit Ethernet USB2.0 Device Ext. memory i/f: 8/16bit DDR1@200Mhz Flash interface : Nand 8/16bit and Serial Color LCD SPI * 1 I2C * 2 Uart * 4 GPIO * 10 Independent 16bit Timer * 10
Fig. 6 is IED board constituted with developed IEC 61850 one chip communication stack processor and its size is 25cm ㄐ 20cm. This board is developed for attaching the use of IED and testing purpose of proposed IEC 61850 one chip communication stack processor and IEC 61850 communication stack library. V.
IEC 61850 COMMUNICATION STACK LIBRARY
In the IEC 61850 processor of the one chip, an IEC 61850 communication stack library is operated. What IEC 61850 communication stack does in a chip is as follows: First, initialization step makes a IED modeling[4] by reading CID(Configured IED Definition) file made by SCL Engineering[5]. Second, a processing step creates messages for communication between IEDs and to map values of model defined in an IED to messages. Lastly, a communication step sends or receives created messages.
Figure 7. Communication structure of IEC 61850. Figure 5. Layout of proposed one chip
Fig. 7 shows operation structure of IEC 61850 communication stack library in IED. IEC 61850 communication stack library consists of OSI 7 layers and object models of communication services and data. By reading information from SCL(System Configuration Language) file, IED modeling is done. Abstract Communication Services Interface(ACSI), defining models and services to access association objects, consists of a common model to define information model of a substation and of service models for information exchange. A service made by ACSI is mapped to a message through services defined in Specific Communication Service Mapping(SCSM). There are three messages communication stack library. x
Figure 6. A IED board using IEC 61850 one chip processor
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used
in
IEC
61850
MMS(Manufacturing Message Specification) : It includes most operation information of IED(e.g. status value). It is usually used between a server and a client. It is 10ms that the time limit of communication through a MMS message.
x
GOOSE(Generic Object Oriented Substation Event) : It is a trip command demanding standard, precision and safety or includes interlocking important information. It is used in every part of a substation. It is 4ms that the time limit of communication through a GOOSE message.
x
SV(Sampled Value) : It is voltage and current sample data made by merging unit and is demanding regular data. It is used between an IED and a merging unit.
System configurator creates SCD file by amalgamating SSD with ICD. HMI observes the whole substation system as using SCD file, and IED configurator separates CID files from a SCD file. In an IED, it constructs IED DB as using CID file. B. Information Modeling Fig. 9 shows MMS mapping process and Fig. 10 is class structure of IEC 61850 communication stack library coded by C++.
A. SCL(System Configuration Language) Engineering A substation using IEC 61850 communication stack library uses SCL engineering. SCL files are coded as XML(eXtensible Markup Language) and there are 4 types in SCL files, ICD, SSD, SCD and CID. x
ICD(IED Capability Description) : It defines LN(Logical Node) as functions of an IED.
x
SSD(System Specification Description) : It defines a substation by using a single line of a substation and LNs required in a substation.
x
SCD(Substation Configured Description) : It defines the whole configurations of a substation.
x
CID(Configured IED Description) : It defines the whole IED.
Figure 9. ttzGU
To do its functions, an IED constructs its modeling by reading information from a CID. Init_SCL class initializes ACSE(Association Control service Element), MMS objects, Variables, and MMS journal and maps data from a CID to LN(Logical Node) and LD(Logical Device).
Figure 8. SCL engineering.
It needs Fig. 8 SCL Engineering process, when it constructs DB by modeling a substation.
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Figure 10. Classes of IEC 61850 communication stack library.
C. MMS Mapping MMSMpl class is the most significant class to create a MMS message. MMSMpl class calls MMSOPCode Class when it makes a MMS message. MMSOPCode class sets a different kind of memory space depending on a type of a message. MMSMsgUtil reads data of MMS Named Variable and Variablelist, and then maps data to memory space. D. Processing and Communication Fig. 11 shows MMS message communication between a server and a client.
class maps each message(MMS, GOOSE, and SV) on OSI 7 Layers. e.g. MMS(1 ~ 7 layers), GOOSE/SV(1 ~ 2 layers) ISOPP class performs functions of presentation protocol and calls ASN.1 class. IEC 61850 standards defines that MMS message must be encoded in ASN.1 grammar. ASN.1 is ordinarily a grammar to provide compatibility for communication between different systems. ISOSP class performs functions of session protocol. ISOTP class performs functions of transport protocol and calls GeneralSocket class. VI. SIMULATION Simulation environment consists of a server and a client program created by the proposed IEC 61850 communication stack library. And a server and a client program are initialized with CID file of SISCO corp.
Figure 11. Communication between a server and a client.
x
Processing in a Client A client determines either asynchronized or synchronized request through MMSClientReq class, and then MMSCOMMREQServ class starts to create a request message determined in MMSClientReq. REQControl class manages request messages and checks either a response message from a server is received or not. A MMS message is created by the process of C. MMS Mapping.
x
Processing in a Server MMSDecoder class analyzes a MMS message received from a client is which request message. And REQControl class makes a list to manage request messages. A decoded request message is executed by MMSServerRsp class. MMSCOMMRSPServ class creates a response message and excutes a service to send the message to a client.
x
Figure 12. a) Client, b) Server
Communication Step COMMServ class starts communication service with a message constructed in a processing step. ACSEServ
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Figure 13. a) Client, b) Server
Fig. 12 and Fig. 13 show client and server programs. A server and a client are initialized and associate with each other. In Fig. 12, a request message is sent to read the value of “LLN0$ST$Mod$stVal” from a client to a server. And it confirms that the value of “LLN0$ST$Mod$stVal” received from a server is “5” in the client program. In Fig. 13, Client program send a request message for writing “2” in “LLN0$ST$Mod$stVal” of server. It confirms that the value of “LLN0$ST$Mod$stVal” is “2” in the server program. VII. CONCLUSION In this paper, IEC 61850 one chip communication stack processor and library are proposed. By substituting the proposed processor for a board in an IED, the development hours is reduced, and not only low cost but also high reliability is achieved. Also, because the proposed library is designed by
OOP;C++ as defined in IEC 61850 standards, an IED developer understands and uses that easily. Later, this proposed processor and library are verified by applying to commercial IED. And Future wok is also to develop GOOSE library, and then MMS and GOOSE library put to the proposed processor. Cost and time of developing devices related IEC 61850 are reduced. And in case of breakdown of devices, it can be fixed just by exchange the IEC 61850 communication stack processor, not debugging the whole board in IED.
[2]
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Gwan-Su Kim and Hong-Hee Lee, “A study on IEC 61850 based communication for intelligent electronic devices,” KORUS`2005, pp. 765–770, 26. June 2005
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