System imbalance / FRCE

FRCE (Frequency Restoration Control Error) is the control signal that drives aFRR and mFRR activation. It is defined in Article 3(2)(31) of the System Operation Guideline (Commission Regulation (EU) 2017/1485) as the control error of the Frequency Restoration Process — equal to the Area Control Error (ACE) of an LFC area, or to the frequency deviation if the LFC area covers the whole synchronous area.

How it is computed

Inside an LFC area: ACE = ΔP + K·Δf, where ΔP is the deviation between scheduled and actual cross-border power exchange, K is the LFC area's frequency-bias factor (MW per Hz), and Δf is the frequency deviation from 50 Hz. A positive FRCE means the area is exporting more than scheduled (or under-frequency); negative FRCE means the opposite. aFRR is dispatched continuously by a closed-loop controller that drives FRCE toward zero; mFRR is called manually when FRCE persists.

SO GL targets

SO GL Article 128 sets target FRCE quality for each synchronous area. For Continental Europe and Nordic: time outside the Level 1 range must be below 30% of year intervals; time outside Level 2 below 5%. Numerical Level 1 / Level 2 values are defined in each LFC block's Operational Agreement and depend on block size and reserve dimensioning.

Baltic LFC block

Since 9 February 2025, Estonia, Latvia and Lithuania form the Baltic LFC block inside CESA. Each TSO operates its own LFC area and computes its own FRCE; the block-level FRCE drives joint reserve activation. Elering submits Estonia's aFRR demand to PICASSO and mFRR demand to MARI; IGCC nets demand against other CESA areas before any cross-border activation occurs.

Sources

System Operation Guideline (Reg. (EU) 2017/1485) · ENTSO-E: System Operation · Baltic Transparency Dashboard