Information Models – IEC 61400-25-2

The information model makes use of an Object Oriented approach for modeling the wind power plant components and data in general. It defines an exact model of the wind power plant (WPP) which contains the components and data of interest. This data will be made available to access for monitoring and control purposes. The information model constitutes a precisely defined set of reusable data classes which will make it possible to build up a logical model being able to represent a specific WPP which is to be modeled.

The WPP is abstracted as a logical device encapsulating different types of classes Wind

Power Plants

Outside scope Communication Profile

IEC 61400-25-4 (Section 2.1.3)

Server

Information Model

IEC 61400-25-2 (Section 2.1.1) Information exchange model IEC 61400-25-3 (Section 2.1.2)

Client Interface

possible to group related operations on data closely related to each other. For instance, the wind turbine residing in a WPP is modeled as a single specific logical node where it will be possible to embed all data and related operations in it. Closely related data will most probably reside on the same logical node. This will make it easier to carry out operations on related data since the data is located in the same container so that data referencing is not complex and thereby making it easy to fetch it. It will be easier to implement and to capture an overview of the device being modeled because its logical structure closely resembles the real world. The sections below will go through each modeling concept used in the information model.

2.1.1.1 Logical Device

As stated previously, a logical device is defined as an abstract model being able to fully represent a power plant device, which is in IEC 61400-25, a wind power plant. The Logical Device (LD) encapsulates all the logical nodes necessary to contain all the data for the WPP device.

Figure 3

Information model hierarchy

Server

Logical Device (LD) Logical Device (LD) Logical Device (LD)

Name Type

Logical Node (LN) Logical Node (LN) Logical Node (LN)

Data class

Common Data Class (CDC) CDC Attribute

1. A LD residing on a server is assigned to a specific WPP which must be able to fully represent it with all its data and attributes. It must contain a collection of specific Logical Nodes (LN) which will further contain data instances reflecting the physical state of the real WPP.

2. Beside the Logical Nodes specific for a WPP, a logical device also contains data about its own condition and the physical device (server) that is hosting the logical device. This common information is contained in specific Logical Nodes serving only for this purpose. For instance, the logical node LPHD (Logical node physical device) represents common data of the physical device hosting the logical device.

These logical nodes are described in Clause 8 of IEC 61850-7-1

Briefly, a Logical Device is a container for all WPP related data together with self descriptive meta-data describing the physical host and the device itself. The hierarchical structure of a logical device residing on a server together with logical nodes and data classes is depicted in the Figure 3 above.

The Figure 4 below illustrates the relation of the model to the real world.

Hides/encapsulates real World

2.1.1.2 Logical Node

It has been mentioned that a WPP is decomposed into smaller information units where they are distributed to different containers. Each such container is defined as a logical node (LN). The modeling approach uses the logical nodes as building blocks to construct all the information of a WPP which is subject to a service. The modeling approach is stepwise decomposition and composition for WPP and the information model respectively. An example of a logical node could be WTUR³ which represents the general information of and wind turbine. This logical node encapsulates information such as net active energy production and net reactive energy production.

1. A logical node consists of a collection of related data, defined as data classes (DC). All the information in a logical node is contained in respective data classes.

The structure of all logical nodes is similar and has a standardized form where different types of logical nodes can be constructed through the combination of different optional data classes they may contain.

All the logical nodes used in modeling the WPP inherit their structure from the abstract logical node class defined in IEC 61850-7-2. From an implementation point of view the implementation of these different logical nodes will be similar since the structure is based on a common definition and follows a common pattern.

2.1.1.3 Data Classes

The data class is the actual component of the information model which is used to define any data contained in logical nodes. It is a generic template to define specific data classes which encapsulates the information. These specific classes are called common data classes, which are precisely defined classes inherited from the general data class.

These classes are defined according to similar needs for different systems in order to have a reusable data class repository. The common data classes used to model a wind power plant device can mainly be categorized under two groups. Common data classes defined specifically for wind power plants and logical nodes inherited from IEC 61850-7-3. A complete listing of these common data classes is provided in IEC 61400-25-2 clause 7.

1. The level of data classes is where the information exchange services operate when retrieving real WPP data. The values of data instances can be written and read depending on their configuration.

2. Similar to logical devices and logical nodes a data class instance must have a unique name among data instances at the same level in the information hierarchy.

This will make it possible to have a unique path from the top level logical device to the instance itself. Therefore each data class has a data reference attribute making it possible to reference it from the top level instance of the information

3 Wind turbine general information. This is information about turbine status, power generation and total net reactive energy production. What the node contain depend upon the specific vendor.

hierarchy. This is important since there is no other way to specify which values on the server/WPP one will retrieve.

3. Each data class has a set of data attributes which are all related to store and describe the data in various means. This includes the type, functional constraints, explanation of the data and trigger conditions that may be associated with the data. Each of these attributes will be used to model the data specifically as needed to reflect the actual data on the wind power plant device

4. The server must be capable of representing the information model with all its instances from logical devices and all the way down to specific data attributes.

The hierarchical structure must be preserved so that each data instance can be referenced in a standard manner as defined in the information model.

5. A server may host one or more logical devices depending on the number of WPP which must be controlled by that server. Therefore it must be possible to uniquely reference a specific logical device representing a specific WPP. Each logical device must have a unique reference/name within the server/namespace it resides.

6. The server must be capable of representing a logical node contained in a specific logical device and to refer to it uniquely. Each logical node has a unique reference name which makes it possible to locate it directly in conjunction with unique reference name of the logical device containing the logical node. This is important since a single server instance can have more than one logical device residing on it.

This means that the server can have different logical devices containing logical nodes with identical names. The naming convention used in the standard prevents unambiguous references to any device or data instance.

The data model is defined in an object oriented manner, and must be reflected as such in the data Model.