MMS Technology and its application in power System communication protocol

Summary: MMS Technology is more and more widely used in the communication protocol of power system, this article will briefly introduce and analyze MMS technology, and on this basis, the application of MMS technology in IEC60870-6 TASE2 series Standard and IEC61850 standard is analyzed.

Key Words: MMS, interoperability, iec60870-6, IEC61850

Introduction

MMS (Manufacturing Message specification) is a manufacturing message specification that is defined by the ISO/IEC9506 standard as a communication protocol for industrial control systems. The aim of the International Organization for Standardization (ISO) is to standardize the communication behavior of intelligent sensors, intelligent electronic devices (IEDs) and intelligent control devices with communication capabilities in the industrial field, so that the devices from different manufacturers have interoperability (interoperation), making system integration simple and convenient. In foreign countries, MMS technology is widely used in industrial process control, industrial robots and other fields.

In the past, MMS has not been used in the power system Telecontrol communication protocol, but the situation has changed recently. The new Iec60870-6 TASE2 series standard of the 57th Technical Committee (IEC TC57) of the International Electrotechnical Commission defines the communication protocol between the EMS, SCADA and other power control centers, which uses object-oriented modeling technology, which is directly mapped to MMS. IEC61850 is the standard for the computer Communication network and system of substation automation system, which is being developed by IEC TC57. The standard uses a variety of new technologies, such as layering, object-oriented modeling, and its underlying directly maps to MMS. From the above two examples, we can see that MMS is more and more widely used in the Telecontrol communication protocol of power system. At present, the domestic power automation industry to MMS is also relatively unfamiliar. Therefore, it is necessary to make an in-depth analysis and research on MMS Technology and its application in power system Telecontrol communication protocol.

MMS Technology

1 Background of MMS

MMS is a set of international standard message specifications for exchanging real-time data and monitoring information between computers or intelligent electronic devices developed and maintained by ISO TC184 in a networked environment. MMS is a separate set of specifications that are independent of the developers of applications and devices. The services provided by MMS are very versatile and are suitable for a wide range of devices, applications and industrial categories. For example, the read service of MMS allows an application or device to read variables from another application or device, whether the device is a programmable logic controller (PLC) or an industrial robot, and the services and messages of MMS are the same. Now MMS has been widely used in automotive, aviation, chemical, electric power and many other industrial automation fields.

2 MMS Standard

The MMS standard is iso/iec9506 and is jointly managed by ISO TC184 and IEC. ISO9506 consists of several parts, of which ISO/IEC 9506-1[1], ISO/IEC 9506-2[2] are the basic standards, and in addition to the basic standards, there are the following supporting standards for specialized areas:
1.iso/iec 9506-3, communication services and protocols for industrial robots [3];
2.iso/iec 9506-4, communication services and protocols for industrial digital control [4];
3.iso/iec 9506-5, communication services and protocols for programmable controllers, not yet available;
4.iso/iec 9506-6, communication services and protocols for industrial process Control [5].

ISO9506-1 defines the service specification, which includes:

(1) Introduction and definition of the concept of virtual manufacturing equipment (vmd,virtual manufacturing device);

(2) the definition of the exchange rules of service or message between nodes in the network environment;

(3) definitions of properties and parameters related to VMD and services.

Iso9506-1 defines the following categories of services:

(1) Environment and general Management Service (environment and Management services);

(2) virtual manufacturing Equipment Support Services (VMD service);

(3) domain Management Service (Domains Management services);

(4) Procedure Management Services (program invocation Management services);

(5) Variable Access Service (Variable access services);

(6) Semaphore Management Service (Semaphore Management services);

(7) operator Communication Services (Operator communication services);

(8) Incident Management Service (event Management services);

(9) Log Management Service (Journal Management services).

Each large class also defines a number of communication service subclasses.

ISO/IEC 9506-2 defines the protocol (PROTOCOL) specification, including:

(1) sequence of execution of the message;

(2) The format of the message or encoding;

(3) The interaction between the MMS layer and the other layers of the OSI reference Model.

The protocol specification defines the message format for MMS using the presentation layer standard ISO8824, the abstract statement identifier (Asn.1,abstract Syntax Notation number one).

MMS provides a set of services for real-time communication over the network (Peer-to-peer). As a general communication protocol, MMS can be used in a variety of general industrial control devices such as programmable controllers and industrial robots.

MMS should be able to support a variety of communication methods, including Ethernet, token bus, rs-232c, OSI, TCP/IP, MINIMAP, etc., MMS can also be connected to other systems via a bridge, router, or gateway.

3 Features of MMS

The use of MMS enables industrial systems to be interoperable and independent.

3.1 Interoperability

MMS is designed to define a standard set of communication mechanisms for devices and applications that make them highly interoperable. For this reason, MMS not only defines the format of the Exchange message, because the unification of the message format is only one aspect of obtaining interoperability. In addition, the MMS standard also provides the following definitions:

(1) object: MMS defines a set of common objects (such as variables) and the network-visible properties of those objects (such as name, value, type).

(2) Service: MMS defines a set of communication services (such as read and write) that access and manage objects in a network environment.

(3) behavior (Behavior): MMS Defines the network visibility behavior that the device should exhibit when executing a related service.

The definition of objects, services, and behaviors forms a set of specifications for how devices and applications communicate in the VMD model. The VMD model defines only the network visibility aspects of communication, and the details of how the actual device implements the VMD model, such as programming languages, operating systems, CPU types, and I/O systems, are not defined. By defining the behavior of the network visible portions of the device, the VMD model of MMS enables high interoperability between devices, while these definitions do not hinder the use of innovative new technologies within devices and applications.

3.2 Independence

Unlike many dedicated communication systems that only apply to specific products, MMS is a common international standard system that is independent of specialized equipment. MMS provides users with a common communication environment that is independent of the functionality they have completed.

Application of MMS in IEC60870-6 series TASE2 Communication protocol

1 Background of the IEC60870-6 series TASE2 Communication protocol

The 57th Technical Committee 7th Working Group (IEC TC57 WG07) of the International Electrotechnical Commission is responsible for developing IEC60870-6 series of computer Data communication Protocol systems compatible with ISO and ITU-T for power system control. The work began in 1993 with the selection of ELCOM90 as a blueprint for a widely used agreement (such as ELCOM90 in Norway, WSCC in the western U.S. power grid, etc.) and began to develop IEC international standards called Remote Control Application service element tase (Telecontrol Application Service Element, later called TASE1). After the completion of the TASE1, it was found that the protocol was poor in adaptability, and the compatibility with iso/itu-t was not good, the United States and Germany firmly opposed, strongly requested a set of ISO and ITU-T compatibility agreement. The United States Electrical Institute (EPRI) led the development of ICCP, in 1996 into the IEC system, known as TASE2[6, 7, 8], and TASE1 parallel to become international standards, but incompatible with each other, forming a European and the United States two series of standards competing situation. Where TASE1 is based on ISO 9072-1/2 ROSE,TASE2 based on ISO 9506 MMS. Because MMS has been widely used in various industries, TASE2 is more adaptable and easier to implement than TASE1. With the adoption of TASE2 by the European Power Generation Coalition (UCPTE), the debate over the years of TASE1 and TASE2 has ended, making TASE2 a globally unified agreement. Now TASE2 has been widely used in Europe and the United States and other regions, soon China will be equated with the standard as the computer communication standards between China's power grid control center, replacing the 1992 promulgated the "real-time data Communication Application layer protocol dl476-92".

The application of 2 MMS in TASE2

ICCP is a protocol based on the MMS standard subset. ICCP is shown in relation to ISO, MMS 1. It can be clearly seen that upper-level protocols are based on lower-level protocols, and lower-level protocols provide services to upper-level protocols. The ICCP layer is on top of the MMS layer, and ICCP enhances the functionality of MMS by mapping its defined structured data objects to MMS objects and adding new semantics. MMS provides services to ICCP and ICCP to control center applications.


Figure 1 The relationship between ICCP, OSI, and MMS

The ICCP protocol relies on the MMS service to realize data exchange between control centers. The MMS service is invoked by the ICCP client and the server, and the MMS service implements the data exchange by executing the required requests. Figure 2 shows the relationship between the ICCP server and the MMS service that performs the data value operation, and Figure 3 shows the sequential operation of the read numeric operation on both the client and server and the call to the MMS service. Similar relationships are defined in detail in iec60870-6-503[6].
Figure 2 The relationship between the numeric operations of ICCP and MMS


Figure 3 Reading the order of numeric operations

The application of MMS in IEC61850

background of 1 IEC61850

With the rapid development of substation automation technology, it is urgent to set up the corresponding international standards. In 1995, the 57th Technical Committee of the International Electrotechnical Commission (IEC TC57) established 3 working Groups 10, 11, WG10/11/12 to develop IEC61850 standards. [9] In March 1999, 3 working groups IEC61850 the draft Committee (Committee Draft). One notable feature of IEC61850 technology is the use of MMS, which ultimately maps to the underlying MMS. Therefore, MMS is one of the foundations of IEC61850.

2 Application of MMS

IEC61850 describes the communication System 2, the communication system is a hierarchical structure, each layer is independent of each other. Iec61850-7-2 is responsible for defining an abstract Communication Service Interface (ACSI) that is independent of the specific Network and communication protocol stack, and iec61850-8-/-9 is responsible for defining special Communication Service mappings (SCSM) associated with specific network and communication protocol stacks.

Figure 4 IEC61850 Communication system overall structure

Iec61850-7-2 defines an abstract communication Service Interface (ACSI). ACSI is a conceptual interface that defines applications that are independent of the actual use of network and communication protocols, including communication services, communication objects, and parameters, which are mapped to the underlying application through SCSM.

Iec61850-8-1 defines the mapping between the substation layer and the communication between the interval layers ACSI to iso/iec9506 that is MMS, as shown in 5. This mapping relationship defines how concepts, objects, and services in ACSI correspond to concepts, objects, and services in MMS. This part gives the method of transmitting real-time data using MMS Service and protocol which is fully compatible with ISO standard under LAN condition.

Figure 5 Mapping between ACSI to MMS

Conclusion

In this paper, the MMS technology is briefly introduced and analyzed, and the relationship between MMS Technology, IEC60870-6 TASE2 series Standard and IEC61850 standard is analyzed on this basis. It can be seen that MMS is the foundation of these two systems. Therefore, the study of MMS is of great significance to the research and realization of these two protocols.

ref
1. ISO/IEC 9506-1:service definition
2. ISO/IEC 9506-2:protocol specification
3. Iso/iec9506-3: Companion standard for robotics
4. ISO/IEC9506-4: Companion standard for numerical control
5. ISO/IEC9506-6: Companion standard for Process Control
6. IEC 60870-6-503. TASE2 Service and Protocol
7. IEC 60870-6-702. TASE2 Application profile
8. IEC 60870-6-802. TASE2 Object Models
9. IEC 61850 (Committee Draft). Communication Networks and Systems in substations. 1999

About the author
Ningyanming , Male, PhD, mainly engaged in the research of substation automation system and relevant international standards.
Fengmei , female, master, mainly engaged in the study of wavelet analysis and microcomputer relay protection device.
Qin Lijun , Male, master, professor, mainly engaged in power system simulation, substation automation system research.
Chu , Male, PhD, professor, Doctoral tutor, academician of Chinese Academy of Engineering, mainly engaged in the research of microcomputer relay protection and substation Automation system

MMS Technology and its application in power System communication protocol