Akiko Takahashi’s research while affiliated with University of Fukui and other places

Optimal Scheme for Remote Island Power System considering PV Forecast Error (2025 Annual Meeting IEEJ) 日本の離島電力系統では，ディーゼル発電機（DG）によって電力供給が行われてきた。また，近年の太陽光発電（PV）システムの普及によってPVの予測誤差の影響が増加し，供給予備力の不足や需給インバランスが問題となっている。本研究では，当日にPV出力の予測を繰り返し更新し，数分ごとに発電機起動停止計画を再立案することによって，不確実性による予測誤差の影響に即時対応できるような計画手法を提案した。シミュレーションでは，最大負荷が大きい淡水化装置が稼働しても，蓄電池によってDG追加起動を要求せず，重負荷期におけるPV予測誤差の影響を最小限に抑えた。結果として、前日計画に比べて総費用を約2.2%削減できることを確認した。

Optimal Joint Planning of Technology Selection, Capacities Planning, and Operation Scheduling for Demand-Side Energy System considering Dynamics of Heat Pump Water Heater and Linkage of Electricity, Heat, and Water (Jxiv) Heat pump water heaters (HPWHs) are attracting considerable attention as a pivotal renewable energy technology for achieving carbon neutrality in commercial and residential sectors. This study proposes an optimization model that comprehensively incorporates the dynamics of HPWHs and their interaction with electricity, heat, and water. Formulated as a joint optimization problem of technology selection, capacities planning, and operation scheduling, the model enables a potential evaluation of an HPWH-based energy system. Numerical simulations, conducted for a single household in Fukui City during the winter season, reveal that introducing a photovoltaic system, an HPWH, and a gas water heater (GWH) can minimize CO2 emissions. In this configuration, the optimal HPWH capacity is 11.7 kW, leading to a 41.4% reduction in CO2 emissions compared to an HPWH-only scenario. However, implementing this configuration would require reducing the current cost of renewable energy equipment by approximately 1/6.5. Furthermore, the derivation of a solution that combines HPWH and GWH is thought to derive from considering time variation in the coefficient of performance (COP), highlighting the importance of considering dynamics in HPWH modeling.

Electric power systems with increasing photovoltaic (PV) systems face concerns regarding degradation in frequency stability due to heightened output forecast errors. As a countermeasure, given the dynamic factors like demand, PV output, and meteorological elements, calculating the optimal reserve margin (ORM) becomes crucial for economic efficiency and resilience reinforcement. To ensure an efficient ORM, Artificial Intelligence (AI) is one of useful strategies used to analyze the combination of all the elements. However, AI is characterized by a black box problem, and to achieve transparency, AI needs to be transformed into explainable AI. To begin with, this paper analyzed all features importance using SHAP adopting a Gaussian process regression model. Then, relevant explanatory variables were selected to improve the prediction accuracy of the ORM. Finally, to verify the effectiveness, this paper planned day-ahead scheduling while securing the ORM determined by the proposed method. It executed detailed demand/supply and system frequency simulations as an operation. The proposed method decreased the risk posed by PV output forecast errors and shortage of reserve margin. Also, the maximum PV capacity increased from 96.2% to 166.2% while maintaining frequency stability.

Increasing integration of inverter power sources into the electrical power system has raised concerns about a lack of system inertia, leading to potential disturbances in system frequency and speed during grid disruptions. Virtual synchronous generator (VSG) control is a promising solution for inertia support of the electrical power system. VSG's inertia enhances system stability by eliminating small and occasional disturbances. Also, the power variation in power electronic interface inverters caused by VSG control increases the stress on power semiconductor devices. This study focuses on the ability of VSG employing three-level topology to ensure system stability and the impact on the lifetime power semiconductors. The result shows that while VSG contributes more to system stability with lager inertia, it also reduces the lifetime of power semiconductors. However, the application of three-level topology was found to mitigate the reduction in the lifetime of power semiconductors.

Research on energy management systems for microgrids up to recent years has covered a wide range of time scales, equipment, and services. However, the roles and purposes of consumers and aggregators targeted in these studies are scattered, making it difficult to apply them to the actual construction of microgrids. This study comprehensively deals with these studies and proposes a scheme that can be applied to microgrid construction plans. The proposed scheme consists of a long-term planning stage that considers an outlook of up to renewable energy 100%, a stage that considers various roles and performs capacity design at the same time as annual planning, and a stage that emphasizes short-term operational planning that considers various equipment. This paper demonstrated the use of the proposed scheme and visualized various indicators such as capacities and schedules to facilitate discussion between each role in the microgrid construction plan.

Integrating Grid-Following Inverters (GFLs) into power systems presents significant stability challenges, particularly in systems with reduced strength and high renewable energy penetration. This study delves into the dynamic interactions between parallel synchronous generators (SGs) and GFLs, highlighting the impact of reduced system inertia and transient stability margins. A novel DC bus controller is proposed to enhance the inertia and stability of GFLs during grid disturbances by dynamically adjusting power references based on load demand. Through mathematical modelling, small signal analysis, and MATLAB simulations, the study evaluates the effects of inverter-based resources (IBRs) on power system stability. The proposed GFL configuration demonstrates improved stability control, achieving an 80 % increase in stability under weak grid conditions. This paper provides insights into optimized control strategies, emphasizing the importance of power-sharing participation factors (PSPF) for effective GFL integr

This paper introduces a DC-link fault detection and synchronization control strategy for grid-forming inverters in hybrid DC/AC microgrids, aiming to bolster system stability and reliability. The proposed control scheme seamlessly integrates DC-link fault detection with virtual synchronous generator (VSG) control, facilitating inertia emulation and synchronization without the need for a phase-locked loop (PLL). The DC bus controller is designed to swiftly identify faults triggered by power imbalances, such as load fluctuations or generator integration, and dynamically adjust the power reference for the VSG controller to ensure inertia emulation. The Ziegler-Nichols method is utilized for meticulous tuning of the DC-link controller gains, while the modified swing equation governs VSG inertia and synchronization. MATLAB/Simulink demonstrate the superior performance of the proposed method compared to traditional GFM control strategies. Specifically, the proposed controller improved the frequency nadir to 59.98 Hz compared to 59.75 Hz and showed an enhanced power step response of 7.9×10^5 W compared to 6.9×10^5 W for conventional control method. The proposed GFM control also eliminated the 10×10^6 W switching spike observed with conventional controllers. These findings highlight the potential of this fault-controller approach to advance the reliability and efficiency of hybrid DC/AC microgrids.

Integrating Grid-Following Inverters (GFLs) into power systems poses significant challenges in maintaining system stability and ensuring reliable power sharing. This study examines the factors influencing GFL stability and integration by analysing the interactions between parallel synchronous generators (SGs) and GFLs operating. The study uses mathematical models, small signal analysis, and MATLAB simulations to evaluate the effects of inverter-based resources (IBRs) on power system stability. A DC bus controller is proposed to automatically sense power imbalances and set the power reference to enhance inertia and stability during grid disturbances. The simulation results and experimental data, summarized in Table 2, demonstrate that the proposed GFL improves stability control in an 80% SCR test, enhances PDPF, and achieves a frequency Nadir of 0.52 Hz. Optimized control strategies like the DC bus controller and careful consideration of power-sharing participation factors (PSPF) are crucial for effective GFL integration. This paper provides valuable insights into improving the stability and reliability of modern power systems with a high penetration of renewable energy sources.