Development of Cross-border Load Frequency Control for the Japanese Power System

This paper presents a cross-border load frequency control (LFC) scheme planned for implementation in the Japanese power system in 2026. LFC is a critical function that regulates system frequency and tie-line power flows by adjusting secondary control reserve (SCR) outputs to minimise the area control error (ACE) in each control area. Traditionally, Japanese transmission system operators (TSOs) have procured SCRs within their own control areas, using LFC to reduce ACE. However, increasing integration of renewable energy has increased frequency disturbances and reduced SCR availability. Rising energy prices also call for more economical SCR operation. To address these challenges, cross-border activation of SCRs – enabling coordination between TSO control areas – has been proposed. This study introduces a cross-border LFC method that improves frequency stability while reducing SCR activation costs. The proposed method corrects ACEs in each control area and coordinates SCR activations across multiple control areas to enhance overall system performance. ACE correction values are calculated through a two-stage distribution: first, the total system ACE is allocated proportionally among control areas, followed by a merit-order distribution of the total already-activated SCR volume. The correction values for each control area are then derived from these distributions while respecting tie-line transmission capacity limits. The proposed method is validated under normal operating conditions and during power plant outages using dynamic simulations based on a model of the Western Japanese power system. The simulation results show that, under normal conditions, the proposed cross-border LFC reduces frequency deviations and lowers total SCR activation costs compared to operation without cross-border