Recent Advances in Applied & Biomedical Informatics and Computational Engineering in Systems Applications

Semantic Interoperability Architecture for the Distribution Smart Grid in Mexico A. ESPINOSA-REZA*, R.GARCIA-MENDOZA* and B. SIERRA-RODRIGUEZ** *Instituto de Investigaciones Electricas *Reforma 113, Col. Palmira, Cuernavaca, Morelos **Comision Federal de Electricidad **Rio Rodano 14, Col. Cuauhtemoc, Mexico, D.F. MEXICO [email protected] http://www.iie.org.mx Abstract: - This paper shows the physical and logical architecture designed for the interoperability of the Distribution Management Systems (DMS) in the Subdireccion de Distribucion (SDD by its Spanish acronym) of Comision Federal de Electricidad (CFE by its Spanish acronym) in Mexico. The architecture adopted includes the definition of the technological platform in order to manage the semantic information interchange between systems and applications; all supported by the Common Information Model (CIM) established in standards IEC 61968 and IEC 61970. Additionally, the process to make a Semantic Model of the Distribution Power System (DPS) is described, as well as the way to build CIM/XML Instances. In this way, the compatibility and correct interpretation of the messages and the information interchanged between heterogeneous systems is independently assured as to the brand, model, developer or platform of the source and destiny systems. Key-Words: Smart Grid, Distribution Power Network, CIM, Interoperability, Semantic. Infrastructure), MDM (Meter Data Management), OMS (Outage Management System), WFM (Workforce Management), among others, including some generically known as "advanced applications" whose definition has not yet been fully established.

1 Introduction Smart Grid is a strategic technological vision. EPRI in [6] describes “The term «Smart Grid» refers to a modernization of the electricity delivery system so it monitors, protects and automatically optimizes the operation of its interconnected elements – from the central and distributed generator through the highvoltage network and distribution system, to industrial users and building automation systems, to energy storage installations and to end-use consumers and their thermostats, electric vehicles, appliances and other household devices.”

Comision Federal de Electricidad (CFE by its Spanish acronym) is the Mexican electric utility that is in charge of all the processes in the electricity delivery system (Generation, Transmission and Distribution). CFE provides energy to about 34.2 million customers, representing more than 100 million people, and annually incorporates more than one million of new customers, with an average annual growth rate of nearly 4.4% over the last six years. [1]

The idea is completed as follows “The Smart Grid will be characterized by a two-way flow of electricity and information to create an automatic, widely distributed energy delivery network. It incorporates into the grid the benefits of distributed computing and communications to deliver real-time information and enable the near-instantaneous balance of supply and demand at the device level”. [6]

In this context, the Smart Distribution Power Network (SEDI by its Spanish acronym) in Mexico is the initiative of the CFE-Distribution (SDD by its Spanish acronym) to implement the vision and strategy of an electricity distribution network in a more efficient, secure and reliable way, that includes the power quality benefits, improved response time to failures, automatic detection and self-healing, flexible to integrate distributed generation and storage, among others, in order to encourage the energy generation from green sources and more efficient consumer devices to support sustainable development to mitigate the environmental impact and reverse climate change. [6][7]

As part of Smart Grid vision, the interaction of different information systems is a fundamental requirement from different utilities areas [3], such as EMS (Energy Management System), NMS (Network Management System), WAMS (Wide Area Measurement System), DMS (Distribution Management System), AMI (Advanced Metering

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 Technical interoperability. It covers the physical connections and the communications between the devices or systems (for example, Ethernet, WiFi, FTP, TCP and USB ports). It emphasizes the syntax or information format (for example: HTML, XML, SOAP and SNMP).  Informative interoperability. It covers the content, semantics and the data format or instruction flows (such as the accepted meaning by humans, programming languages as well as common symbols). It focuses in which information is interchanged and its meaning (for example The Common Information Model CIM, The Common Power System Model CPSM, Object models based on XML schema definition or Object models based on OPC Unified Architecture, among others).  Organizational interoperability. It covers the relationships among organizations and people and their parts of the system, including the commercial relationships (such as contracts, characteristics and market structures) and the juridical or legal relationships (for example, the regulation structures, requirements as well as protection of the physical and intellectual property). It emphasizes the pragmatic aspects, especially the step taking and electrical market.

2 Semantic interoperability Interoperability refers to the capability of the equipments or different manufacturing systems in order to successfully communicate among themselves in a network and it is the condition through which heterogeneous systems are capable of interchanging processes or data. Smart Grid is a system of systems, it means that the Smart Grid architecture will be a composition of many system architectures and subsystem, thus will allow the maximum flexibility during the implementation, but at the same time, it will demand a high capacity of integration of the new systems with legacy systems. [5][6][7] The GridWise Architecture Council developed a conceptual reference model for the identification of standards as well as the necessary protocols in order to assure the interoperability, the cybersecurity and define system and subsystem architectures in the Smart Grid. “The framework pertains to an electricity plus information (E+I) infrastructure. At the organizational layers, the pragmatic drivers revolve around the management of electricity. At the technical layers, the communications networking and syntax issues are information technology oriented. In the middle, we transform information technology into knowledge that supports the organization aspects of the electricity related business”. [4]

When the interoperability level increases, the electrical infrastructure intervenes more and the Information and Communications Technologies (ICT) infrastructure intervenes less, due to the business processes and relationship management, as well as the policies and regulations of the electrical market. In the semantic interaction levels, the Common Information Model (CIM) established in IEC 61968 and IEC 61970 is a proposal of an abstract model of standard information for electrical enterprises based in UML (Unified Modeling Language). In such a Model real world elements are represented as well as their relationships, with the purpose of creating an information system which can be used among different applications for data management and interchange. Several enterprises, organizations and institutions are related to model development and maintenance; many electrical utilities have reports and papers describing applications and results. [12]

Three levels are identified in order to get the effective interoperability in any system:

Figure 1. GridWise Architecture Interoperability Layered Categories. [4]

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Council

“The CIM Users Group is dedicated to the promotion of the portability of existing applications and to the promotion of the ease of installation of new applications through the use of such standards as the common information model, message bus, and common data access specification”. [13]

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3 Semantic Service Architecture (SSOA)

module of inlets/outlets/validation that assures the semantic of the messages.

Oriented

In CFE, the physical architecture has been defined in order to implement a semantic interoperability model which is shown in the following figure.

The Service Oriented Architecture (SOA) is an information architecture and strategy; it defines the use of services with low level coupling and components kind of “black box”, in order to give support to the enterprise's business requirements. [17] On the other hand, the syntax refers to the grammatical structure of a message, expression or computing program, without taking care of its interpretation. At the same time, the semantic is the meaning study; referring to aspects of the meaning, sense or meaning interpretation of a certain element, symbol, word, expression or formal representation that is grammatically correct.

Figure 2. Physical architecture for the semantic interoperability of the Smart Distribution Power Network (SEDI).

In this context, SOA assures the message deliveries syntactically well written because it establishes the architecture, structure, means and message formats, for example WSDL and XML, but it does not assure that the meaning or its interpretation is the same for the source system and for the destiny system [15]. Hence the importance of integrating a Semantic SOA architecture (SSOA) that provides an information model and a common language, in such a way that the messages sent among applications are obliged to respect besides the syntax, a scheme or a common semantic Model. In [13], the schematic definition, as well as the fundamental differences between SOA and SSOA are shown.

For the proper processing of inlet/outlet messages and information interchange between systems of DMS domain, it was established the logical architecture for the semantic interoperability, which considers that all the legacy systems of CFE must pass through a “CIM Wrapper”, that is a layer or wrapper based in Generic Interface Description (GID) technology to define the generic interfaces of data access. [10][11] Each “CIM Wrapper” must consider the develop of the Semantic Model for the particular system that will link, as well as an internal processing of data that allows the “mapping” of the particular information to the general model, respecting the unique nomenclature of the CIM Model. [15][19]

4 Architecture Base for Semantic Interoperability The semantic interoperability requires counting with an architectonic model for the efficient interchange of information among the domain systems. This model must include the capability of receiving and sending messages that are validated in the syntax and in the semantic defined for the information conformation; in this way, it is assured three points: accomplishment of the rules for technical build of messages (format, scheme and technology), accomplishment of the writing rules established (profile, sequence, linkage, cardinality) and the correct interpretation of the meaning of the message.

Likewise, when counting with the semantic interoperability layer, in the future, any system that by its nature are CIM compliant, it will be able to link up in a direct way without the necessity of abstracting the accomplishment through “CIM Wrappers”. In the case of the “On-Line Simulator” for Distribution Networks [14], it was established from its beginning the accomplishment of the CIM, hence presently counting with the capability of generating and recuperating (export/import) CIM/XML Instances for its processing in the semantic interoperability bus of CFE. Nowadays, the Simulator is used (additionally) to generate and validate CIM/XML Instances, as well as for develop the Semantic Model and mapping for legacy systems.

In this sense, the IEC standards that define the CIM recommend the use of an Enterprise Service Bus ESB (middleware) with the purpose of a data interchange for the technical layer, as well as a

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A Profile is a subset of classes, attributes and associations derived from the Ontology (CIM base model) and that it represents the components of the real world that have been selected for their use in information systems. In CFE, in order to obtain the Semantic Model of the Electrical Distribution Network (SED by its Spanish acronym) as well as CIM/XML Instances of the real Electrical Distribution Network, the CIM base model of standards IEC 61968 and IEC 61970 was used, and the following sequence was applied: Figure 3. Logical architecture for the semantic interoperability of the Smart Distribution Power Network (SEDI).

5 Semantic Model of the Electrical Distribution Network The technology of the technical interoperability layer (syntax) does not assure the same level of meaning or interpretation in the semantic layer, due to: [17][18]  XML provides a superficial syntax for structured documents, but does not impose semantic restrictions in the meaning of these documents.  XML Schema is a language that is used to restrict the structure of the XML documents and to extend XML with data types.  RDF is a model of data for objects or “resources” and the relationships among themselves, giving a simple semantic. This type of data model can be represented in XML syntax.  RDF Schema is a vocabulary that is used to describe characteristics and classes of RDF resources, with a semantic for the generalization and hierarchy of characteristics as well as of classes.

Figure 4. Sequence for obtaining the Semantic Model and create CIM/XML Instances according to CIM. 1)

A Semantic Model is an Ontology, it means that it allows representing explicitly the meaning of vocabulary terms and the relationships among those terms in an exhaustive and accurate way with the purpose of easing the communication and the interchange of information between different systems. An Ontology adds vocabulary to describe characteristics and classes; among others, relationships between classes (for example, composition, association, inheritance), cardinality (for example, “only one”), equality, and it adds types of properties, characteristics of properties (for example, symmetry), as well as enumerated classes. [19]

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2)

3)

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Mapping concepts of the Electrical Distribution Network with the defined concepts in CIM base model. As long as possible it must be used the definition of CIM, taking into consideration that occasionally it will be impossible to establish the exact correspondence. Extend the CIM base model. Through the use of derived classes, all the Electrical Distribution Network concepts that have not been considered in the CIM base model must be added, for example: feeder data, type of customers, etc.. Generation of the CIM/XML Profile. As of the extended CIM base model and with the CIMtool (open source) [20], the validated Profile is generated with the rules of the CIM Ontology. At this point, Semantic Model is available and can be used in different ways and technologies that fit with CIM. [12]

Recent Advances in Applied & Biomedical Informatics and Computational Engineering in Systems Applications

4)

5)

Coding the Profile in NET Classes. According to the Profile developed, its classes and relationships (in UML), all the classes must be coded in a Object Oriented Language in order to use the CIM/XML Profile according to the RDF scheme of the IEC 61970-501 standard. Write CIM/XML files (Instances). It is necessary developing of an application that consume the NET classes, this application must have native access to the data source of legacy systems in order to extract data of the real Electrical Distribution Network and fill the objects created based in the CIM/XML Profile, in this way a CIM/XML file (Instance) is generated and can be processed according to the rules of the CIM Ontology.

The result allows the formal representation Electrical Distribution Network of CFE and it being in accordance to the semantic rules that the interoperability among multiple systems domain of Electrical Distribution.

6 Conclusion From its definition, the Smart Grid considers a technological revolution in the electrical energy supply systems, from its generation, transportation and storing until to its final use. CFE is working in the adoption of international standards and best practices in the industry, such as IEC 61850, IEC 61968, IEC 61970, IEC/PAS 62559, UML, among others, with the purpose of conforming an electrical network more efficient, safe, robust and reliable. In this effort, the definition and strategy of the Smart Distribution Power Network (SEDI), it will mark the guidelines of the CFE-Distribution on its way to the required technological change that is needed to conform the electrical network of the future.

of the allows permit in the

On its behalf, the adoption of the CIM Model and the Semantic Interoperability Architecture are the elements that will allow the interchange of information in a standard way among the systems, with the purpose of establishing and implanting advanced applications, such as the Demand Response (DR), Advanced Distribution Automation (ADA), Real Time Pricing (RTP), Self-Healing, among others that are emerging in the international context. [9]

7 Acknowledgements

Figure 5. Example of CIM/XML Instance of Electrical Distribution Network of CFE, according to CIM.

The authors would like to thank the following people for their help in developing this work:  From IIE: Alejandro Villavicencio, Tito Manuel Calleros, Mirna Molina, Heidi Barrera and Eider Miguel Amores.  From CFE: Fidel Borjas, Hector Perez and Leopoldo Meza.  From SISCO: John Gillerman and Margaret Goodrich.  From Soluciones Leal: Rita Aulenbacher Holm.

Currently CFE counts with the Semantic Model and Instances for:  The topological model of Distribution Network (georeferenced) from 135 kV up to 13.8 kV.  The one-line diagrams for Distribution Substations.  The electrical and physical models of the electrical elements (electrical assets) and integrated devices (such as telecontroled devices).  SCADA data acquired in real time.  Historical data of Distribution Substations.  Important customers that are connected to the Distribution Network  Operational data (failures and maintenance).  Historical data of energy quality events (Sags and Swells).

References: [1]. CFE Official Website (http://www.cfe.gob.mx). [2]. EPRI's IntelliGrid initiative (http://intelligrid.epri.com). [3]. The Modern Grid Initiative Version 2.0, Conducted by the National Energy Technology Laboratory for the U.S. Department of Energy

New concepts and systems mapping are being integrated to the Semantic Model of CFE.

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Office of Electricity Delivery and Energy Reliability, January 2007 (http://www.netl.doe.gov/moderngrid/resources. html). [4]. GridWise Architecture Council, GridWise Interoperability Context-Setting Framework, March 2008 (http://www.gridwiseac.org). [5]. 111th US Congress, Public Law 111-5American Recovery and Reinvestment Act of 2009 (ARRA), February 17, 2009, (http://www.gpo.gov/fdsys/pkg/PLAW111publ5/content-detail.html). [6]. EPRI, Don Von Dollen, Report to NIST on the Smart Grid Interoperability Standards Roadmap, (Contract No. SB1341-09-CN-0031-Deliverable 7), June 17, 2009. [7]. NIST Special Publication 1108, NIST Framework and Roadmap for Smart Grid Interoperability Standards, Release 1.0, January 2010. [8]. IEC-EPRI, IEC/PAS 62559, IntelliGrid Methodology for Developing Requirements for Energy Systems, Publicly Available Specification, Pre-Standard, Edition 1.0, 200801. [9]. IEEE P2030, Draft Guide for Smart Grid Interoperability of Energy Technology and Information Technology Operation with the Electric Power System (EPS), and End Use Applications and Loads, P2030 Working Group Meeting Minutes: June 3, 2009, Santa Clara, CA. [10].Newman, Scott, Position Paper for the GridWise Interoperability Workshop, April 2007 (http://www.gridwiseac.org/pdfs/interop_papers _0407/papers/neumann.pdf).

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[11].L. King, T. Nielsen, Scott Neumann, Ali Vojdani, Parag Parikh, The Common Information Model for Distribution, An Introduction to the CIM for Integrating Distribution Applications and Systems, EPRI document 1016058, Technical Update, November 2008. [12].Rosa G. Garcia E., Jose A. Sanchez L., Alfredo Espinosa R., Review of the state of the art and practice in CIM applications in Electric Utilities (Analisis del Estado del Arte y de la Practica en la aplicacion del modelo CIM en Empresas Electricas), Boletin IIE, Abril-Junio de 2010 (In Spanish). [13].CIM Users Group Official Website (http://www.cimug.org). [14].Alfredo Espinosa R., On-line Simulator for Electrical Distribution Network (Simulador del Sistema Electrico de Distribucion). Breves Tecnicas, Boletin IIE, Enero-Marzo de 2010, pp. 27 y 28 (In Spanish). [15].Dave McComb, Semantics in Business Systems, Morgan Kaufmann Publishers, 2004. [16].Bobby Woolf, Exploring IBM Smart SOA Technology & Practice, Maximum Press, 2008, Canada. [17].Jeff Davies, David Schorow, Samrat Ray and David Rieber, The Definitive Guide to SOA Oracle Service Bus, second edition, Apress, 2008. [18].Judith Hurwitz, Robin Bloor, Marcia Kaufman and fern Halper, SOA for Dummies, 2nd IBM Limited Edition, Wiley Publishing, Inc., 2009, US. [19].OWL Web Ontology Language Overview, World Wide Web Consortium (W3C), February 2004, updated to October 2009. [20].CIMtool (http://www.cimtool.org/).

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