automatic Frequency Restoration Reserve

Activation of automatic Frequency Restoration Reserve

For the activation of aFRR, TSOs operate various systems:

• A Load Frequency Controller (LFC) per TSO to determine the imbalance in each grid area and to locally activate local aFRR providers in a price-optimized manner.
• An overarching optimization to avoid counteracting aFRR activations in different grid areas (IGCC / Imbalance Netting).
• An overarching optimization for the global, price-optimal activation of all aFRR providers (PICASSO).
  
  

Figure 1 shows the schematic representation of the Load-frequency Control. The task of the Load-frequency Control is to stabilize the grid frequency at 50.0 Hz and to maintain the schedules for each grid area. For this purpose, each TSO measures the current actual frequency as well as the current actual power exchange of its gird area, i.e., the sum of all power flows on the interconnectors to neighboring TSOs. On one hand, the actual frequency is compared with the target frequency. On the other hand, the LFC compares the actual power exchange with the target exchange, i.e., the planned import and export according to schedule trading transactions.

For any frequency-dependent FCR imports or exports, no schedule is available, so this additional intentional flow is estimated using the so-called K-factor (among other things, dependent on the FCR held in the grid area) and used to correct the difference between actual and target exchanges.

The deviations between the actual and setpoint values result in an LFC input, which is used as the input value for the local proportional-integral LFR. Based on the LFC input, the local LFR calculates the necessary positive or negative aFRR input in the respective gird area. The integral part of the LFR ensures that the frequency is returned to the setpoint frequency.

For the activation of local providers, the LFC has a common merit order list, so it can send the respective call values to the most cost-effective providers via remote control interface. For this, a point-to-point communication link between providers and the LFC is necessary.

The provision of the entire aFRR must take place 5 minutes after the activation of the provider, with an initial response required after 30 seconds. Since the aFRR call in practice is a constantly changing value, the provision must therefore occur within a so-called acceptance band. This is formed from the minimum and maximum call values for each provider over the last 5 minutes.

The overarching optimizations from IGCC and PICASSO trim the local LFC via an online signal in such a way that, with available transmission capacities between the participating TSOs, a counteracting call is avoided, and the aFRR activation is carried out by the LFC that currently has access to the most cost-effective providers.

The calculations in PICASSO and IGCC are also performed every few seconds. Consequently, the aFRR regulation band can be freed up again through a manual mFRR call.

Consequently, the aFRR regulation band can be freed up again through a manual mFRR call.