ODM Overview

Background

Many years ago, IEEE recommended a Common Data Format (IEEE CDF) for exchanging Loadflow study data[1] using flat file. Power system software companies uses their own internal data format, some have features similar to a mark-up language. However, it is our observation that these formats are proprietary and are often not well documented. We think that the power engineering community needs a completely open, free, flexible and well-documented model/format for power system analysis information exchange. XML is an obvious choice, since it is a very mature technology and has become the de facto standard for defining information exchange standards. Also, numerous open-source and free XML processing tools are currently available. For those who are unfamiliar with XML, some introductory information relevant to power system representation can be found in Ref[2].

ODM in a Nutshell

You might be familiar with the IEEE CDF format. The following is a line describing a bus record:

2 Bus 2     HV  1  1  2 1.045  -4.98     21.7     12.7     40.0    42.4   132.0  1.045    50.0   -40.0   0.0    0.0        0

Using ODM, the same information could be represented in an XML record, as follows:

<aclfBus id="Bus2" offLine="false" number="2" zoneNumber="1" areaNumber="1" name="Bus 2     HV">

   <baseVoltage unit="KV" value="132.0"/>

   <voltage unit="PU" value="1.045"/>

   <angle unit="DEG" value="-4.98"/>

   <genData>

      <equivGen code="PV">

         <power unit="MVA" im="42.4" re="40.0"/>

         <desiredVoltage unit="PU" value="1.045"/>

         <qLimit unit="MVAR" active="true" min="-40.0" max="50.0"/>

      </equivGen>

   </genData>

   <loadData>

      <equivLoad code="CONST_P">

         <constPLoad unit="MVA" im="12.7" re="21.7"/>

      </equivLoad>

   </loadData>

</aclfBus>

There are many advantages to represent data in XML format. In fact, XML currently is the de facto standard for representing data for exchanging information. One obvious benefit is that it is very easy to read by human. Anyone with power engineering training can precisely interpret the data without confusion. There is no need to guess if the number 40.0 is generation P or load P, in PU or Mw.

Current State

• Currently there are many formats for storing data for power system simulation. Among them, PSS/E, BPA and IEEE CDF are well known.
• Power system software companies and open-source groups, such InterPSS, developed and provides utilities to import data in these formats into their applications. It has been observed that the direction is mainly one way, importing data in different formats into their simulation applications, but not in the other way, that is exporting data to different data formats. This has made robust and reliable power system simulation study case information exchange very difficult, if not impossible.
• Except IEEE CDF, these data formats are often not well documented. Also, most data format documents are not publicly available.
• A simple math calculation tells us that if there are N data formats and M applications, the possible filtering/converting routes in the above diagram are NxM.

Proposed Solution

• An Open Model for Exchanging Power System Simulation Data, ODM - Open Data Model for short, is proposed. The model is defined using XML schema. The schema will be maintained by the IEEE PES OSS Task Force.
• In the information model theory, the ODM model, shown in the above figure, is sometimes called a Canonical model. The model should be designed to be flexible and extensible to cover all data formats. Using the Canonical model, the possible filtering/converting routes for N formats and M applications are N+M.
• If the model becomes popular and widely accepted, power system software companies and open source groups will develop and provide import and export utilities to exchange information with the model
• We are expecting that open-source groups will provide implementations to exchange information between the well known data formats, such as IEEE CDF, PSS/E, and the ODM model.

Third Party Tools/Modules

If the model becomes widely accepted, third party tools, such as graphic one-lien diagram editor, and simulation modules, developed based on the model are expected to be available, mostly likely from open-source software groups.

Guideline and Scope

Guiding Design Principles and Assumptions

• The information exchange model is intended for power system simulation. It serves different purpose than the IEC CIM model, which is intended to describe the operation state of a power system from both physical and logical perspective. the ODM model, on the other hand, only represents power system in a logical view, with nodal bus and branch as the most fundamental concepts. For example, the IEEE CDF is consists of a set of bus records and branch records. PSS/E RAW Data file consists of bus records, branch records and other records with reference to either bus records or branch records.
• Modern power system simulation algorithms are mostly built on top of the power network nodal admittance Y-matrix. The model is designed in such a way to minimize possible ambiguity to implement Y-matrix based solutions.
• It is intended for power system simulation information exchange only, not for modeling a power system for simulation purpose. For example, it won’t have elements to represent the Y-matrix itself.
• The data needed to create the model could be persisted in any format and any location, such as file system or database system. However, it has to be in XML format confirming the schema when used to exchange information between different systems. Persistence of the model data in an XML file is recommended.

Scope

• As the first step, the ODM model schema shall cover all concepts in IEEE CDF, PSS/E raw and UCTE data formats for Loadflow analysis.
• The ODM schema is currently being extended to cover short circuit analysis, transient stability simulation and other concepts
• A reference Java implementation of the model will be provided. Utilities to convert IEEE CDF file and PSS/E raw file into the model will be also created by participating open-source groups.

The reference implementation is currently under development by InterPSS Systems LLC. The implementation is currently hosted at GitHub.

ODM Schema Design

At the top is the schema is defined using the StudyCaseXmlType structure, as shown in the following diagram:

• schemaVersion - Schema version string.
• contentInfo - extra info for describing the content, including original data format.
• networkCategory - Transmission or Distribution network category
• analysisCategory - Loadflow, ShortCircuit, TransientStability, OPF ...
• baseCase - Element of type NetworkXmlType for describing a power network as the base case.
• childNet - For describing a set of child power networks.
• modificationList - optional, a list of modification to the base case
• scemarioList - optional, a list of scenarios, built on the base case for description, for example, control parameters for a Loadflow analysis

Related Documents

Data Structure and Relationship Analysis

It is our goal to capture all key data relationships found in the existing, commonly used, data formats, including IEEE CDF, PSS/E and UCTE. It has been observed that although these data formats are quite different at individual record and field level, they have the same underlying data entity/object relationships. After all these data formats are intended to create the nodal Y-matrix and perform power system analysis. This documents presents detailed analysis of the data structures and key relationship for power system simulation.

ODM Schema Specification

The Open Model for Exchanging Power System Simulation Data (ODM) schema is formally defined in the document.

Reference Implementation

As an important part of the ODM Model development, a reference implementation of the model using Java will be provided. It serves two main purposes:

• To prove that the model could be practically implemented. “We eat our own dog food”;
• To serve as a concrete example for those who might new to XML and have difficult to understand how to use the model.

ODM Tutorial

An ODM tutorial has been created for those who might be new to XML and associated concepts. A simple 5-bus system is used to show how step-by-step to manually create a XML document, governed by the ODM Model XML Schema.

Sample Study Case

This section list sample study cases where ODM Model is used to solve power system simulation problems or is part of such a solution.

UCTE 2002 Sample Loadflow Case

In-depth AC Loadflow and DC Loadflow studies of the UCTE network, representing the continental European countries, using InterPSS. Also, performance testing data are presented regarding the usage of the IEEE ODM model to transfom the original case data file in the IEEE Common Data Format into the OMD model.

References

[1] "Common Data Format for the Exchange of Solved Load Flow Data", IEEE Trans on PAS, Vol. PAS-92, No. 6, Nov/Dec 1973, pp. 1916-1925.

[2] "XML and Data Exchange for Power System Analysis", IEEE Power Engineering Review April 2000

[3] Tutorial on XML