Analysis and improvement of cross-regional cooperation for automatic frequency restoration reserves

Frequency restoration reserves (FRRs) are currently procured and activated by individual transmission system operators (TSOs) in Japan. To enhance the efficiency of the balancing process, a balancing market will be established in 2021, with the introduction of cross-regional cooperation for an automatic FRR (aFRR) being discussed. The cross-regional aFRR cooperation will be conducted through the procedures of the imbalance netting and aFRR sharing. As for the imbalance netting, two methods -i.e., the ACE netting and aFRR demand (aFRR-d) netting -have been used in the US and Europe, respectively. This study examines the merits and demerits of those netting methods through the time-domain simulations using a model comprising two Japanese TSOs' control areas. Although the ACE netting is more efficiently in reducing frequency fluctuations, the reduction effect in aFRR activations is limited. In contrast, the aFRR-d netting can reduce aFRR activations more efficiently while the time required to restore the frequency can be prolonged. To utilize the merits and compensate for the demerits of the above two netting methods, this paper proposes a combination of those netting methods. The simulation results indicate that the proposed method can reduce the frequency fluctuations as effectively as the ACE netting and can reduce the aFRR activations as effectively as the aFRR-d netting in comparison with the localized aFRR operation.