Active and Reactive Power Control with IEC 61400-25-2

The focus of the IEC 61400-25 series is on the communications between wind power plant components such as wind turbines and actors such as SCADA systems. IEC 61400-25-2 specifies the information model of devices and functions related to wind power plant applications. These models extend IEC 61850-7-x models. Almost all definitions, hardware and software solutions available for IEC 61850 can be used for IEC 61400-25-2. In particular, IEC 61400-25-2 specifies the compatible logical node names, and data names for communication between wind power plant components.

The standard IEC 61400-25-2 defines a comprehensive list of information models (Logical Nodes) for wind turbines, e.g.:

• WTUR - Wind turbine general information
• WROT - Wind turbine rotor information
• WTRM - Wind turbine transmission information
• WGEN - Wind turbine generator information
• WCNV - Wind turbine converter information
• WTRF - Wind turbine transformer information
• WNAC - Wind turbine nacelle information
• WYAW - Wind turbine yawing information
• WTOW - Wind turbine tower information

The most crucial Logical Nodes are likely the

• WAPC - Wind power plant active power control information
• WRPC - Wind power plant reactive power control information

These models describe the "interface" between a complete park and the grid operator for control purposes. These Logical Nodes can be used for other power resources like CHP, PV, ... The German EEG (Erneuerbare-Energien-Gesetz) accelerates the application of IEC 61400-25 tremendously, because the Grid Operator needs more information about the park and he needs to control the whole power system in cases of faults and critical conditions - wind power plants and other resources are an integrated part of the whole system. These resources cannot be treated just as negative loads.

The WAPC (active power control) comprises the following Data Objects:

Status information

• Actual number of wind turbines in operation
• Active Power Limitation Mode Enabled
• Active Power Control Mode Enabled controlling apparent power
• Gradient Function Enabled
• Delta Function Enabled

Measurements

• Wind Power Plant active power output capability
• Wind Power Plant active power output
• Wind Power Plant apparent power
• Wind Power Plant Gradient
• Wind Power Plant active power reserve utilizing the Delta function –
  the difference between active power generation capability and active
  power generated

Control information

• Activate active power control function
• Activate apparent power control function
• Activate gradient control function
• Activate delta control function
• Set reference value for the wind power plant active power output
• Set reference value for the wind power plant apparent power output
• Set reference value for gradient ramping up the wind power plant active power output
• Set reference value for gradient ramping down the wind power plant
  active power output
• Set reference value for the wind power plant active power reserve –
  also named as “spinning reserve”

The information provided by these models is crucial for a future stable power delivery system.