Header image of a transmission tower

German network rules association

Grid Control Cooperation

The grid control cooperation (GCC) is an innovative network control concept, by means of which the four German transmission system operators (TSOs) optimise their control energy use and the control reserve provision technically and economically through an intelligent communication between the load-frequency controllers of the TSOs.

The horizontal structure of the control areas in the European interconnected system, offers the GCC the possibility to exploit synergies in terms of network control like in a single fictitious control area, without giving up the proven structure of control areas. It also enables a flexible response in case of network bottlenecks.

The functionality of the GCC is assured by four modules, each of which targets a different technical and economic optimisation:

Module 1: Prevent counteracting control reserve activation

It is a characteristic of the system that there are times when individual control areas have insufficient power, while other control areas have an excess of power at the same time. Without the GCC, the control reserve for each control area would be activated in line with the concept, independently and with different polarities. The objective of Module 1 is to avoid the activation of reverse control power through controlled and targeted energy exchange between the control areas. The potential for cost saving lies in the reduction of the reverse control reserve (requency Restoration Reserve and manual Frequency Restoration Reserve) and of the associated costs.

Module 2: Common dimensioning of control reserve

The objective of Module 2 is the joint dimensioning of control reserve across control areas in order to achieve a reduction of the power reserve and the corresponding costs (automatic Frequency Restoration Reserve and manual Frequency Restoration Reserve). The dimensioning corresponds to a fictional German control area. The GCC gives the participating control areas access to the commonly held reserves, so that they can be reduced.

Module 3: Common procurement of secondary control reserve

Module 3 allows the German TSOs to purchase automatic Frequency Restoration Reserve from suppliers that are only connected to their Reserve Connecting TSO via telecontrol equipment. The potential for cost saving through the use of module 3 lies in the cost reduction through direct competition between providers in the entire German automatic Frequency Restoration Reserve market and in the reduction of the technical costs for providers.

For manual Frequency Restoration Reserve (mFRR), the joint procurement has already been in place for a long time, as the activation requested by telephone does not require an online connection.

Module 4: Cost-optimised activation of control reserve

The control reserve is used cost-effectively throughout Germany on the basis of Germany-wide merit order lists for automatic Frequency Restoration Reserve and manual Frequency Restoration Reserve. The aim of Module 4 is therefore the economic optimisation of the control reserve activation across control areas. Consequently, the potential cost saving lies in a cost reduction for control work.

Uniform balancing energy price (reBAP)

Another advantage of the GCC is the introduction of a uniform balancing energy price (reBAP) across control areas. In this way, the balancing group deviations in all German control areas are charged with the same balancing energy price.

System safety and congestion management

In the case of limited transmission capacity (network congestion), the automatic Frequency Restoration Reserve optimisation - and therefore the transmission of control reserves between the control areas - can be coordinated or restricted in real time according to the direction. In this case, diverging from the merit order list or not fully avoiding the reverse use of control reserve is consciously accepted.

Thus, the GCC allows the four German TSOs to use a uniform control reserve just like in a fictional single German control area. In this way, cost saving will be achieved, whenever physically possible, without jeopardising the grid security in the event of temporary power shortages, as the existing control area structure still exists. Moreover, the relevant control circuit within the control area remains unchanged, and is only expanded by a corrective activation. Thus, each control area is still preserved as a safety cell and can, to a certain extent, achieve balance autonomously, depending on the available control reserve within its control area.

Technical functioning

The technical principle of the grid control cooperation is based on a "automatic Frequency Restoration Reserve optimisation software", which calculates the best overall automatic Frequency Restoration Reserve use for the GCC. The basic principle is shown in the illustration

Because of prior unknown variations in consumption and production, the balance in a control area more or less continuously differs from the required power balance. The resulting balance difference must be compensated by activation of automatic Frequency Restoration Reserve. The need for automatic Frequency Restoration Reserve of the participating control areas is reported online to the coordinating optimisation module. This module calculates a correction value, which then rectifies the balance difference. Accordingly, a change is made in the input value of the secondary controller that retrieves the optimal, most cost-effective automatic Frequency Restoration Reserve amount from the GCC control areas, as calculated by the automatic Frequency Restoration Reserve optimising system. The corrective activation is calculated online with seconds as the unit of time.