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    Inertia Assessment From Transient Measurements: Recent Perspective From Japanese WAMS
    (2022-01-01)
    Kerdphol, Thongchart
    ;
    Watanabe, Masayuki
    ;
    Mitani, Yasunori
    ;
    Currently, the substantial renewable penetration brings a low inertia issue to the Japanese power system, threatening stability and resiliency than ever. The inertia estimation based on transient events provides a reliable basis for system control and operation. However, the poor rate of change of frequency extraction from different types and locations of phasor measurement units (PMUs) could significantly lead to inertia estimation errors. As a remedy with a lesson learned, this paper analyzes effective inertia estimations based on transient measurements of the Japanese wide-area monitoring in both distribution and transmission levels. Due to the longitudinally interconnected configuration of the 60 Hz Japanese power system, the polynomial approximation technique is proposed to restrain the strong effect of oscillatory components. To enhance the estimation performance considering an existing center of inertia, the comprehensive mode-shape analysis is performed via geographical measurement locations, indicating sufficient PMUs with precise estimation. The effectiveness of inertia estimation techniques is verified through actual system events corresponding to various transient sites. The numerical results demonstrate that recent inertia of the 60 Hz Japanese system with existing renewables ranges around 7.12 - 8.13 s in its system load base.
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    Small-Signal Stability Enhancement Through Integration of Distributed Grid-Forming Loads Considering Multi-Agent Collaboration
    (2025-01-01) ; ;
    Mitani, Yasunori
    The integration of distributed controllable loads in future islanding microgrids (MGs) is growing. This creates new opportunities to actively shape grid frequency and voltage. As a result, it leads to the development of distributed grid-forming loads (DGFM-Ls). Simultaneously, it is equally crucial to ensure robustness, particularly in preserving small-signal stability amid the multi-agent collaboration. This paper presents a strategy for the small-signal stability enhancement in islanding MGs with DGFM-Ls. The small-signal models of the MG with DGFM-Ls are mathematically developed and analyzed. The multi-agent cooperation is modelled to improve the small-signal stability of the MG with DGFM-Ls. Additionally, uncertainties from multi-agent cooperation, such as partial or complete lack of measured signal observability, are considered. Data quality issues are also taken into account under various conditions. Simulation results are conducted in a MG with a significant penetration of inverter-based resources under various MG operating points and conditions such as topology changes and unavailability of certain agents.
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    Small-signal analysis of multiple virtual synchronous machines to enhance frequency stability of grid-connected high renewables
    (2021-04-01)
    Kerdphol, Thongchart
    ;
    Rahman, Fathin Saifur
    ;
    Watanabe, Masayuki
    ;
    Mitani, Yasunori
    ;
    Hongesombut, Komsan
    The virtual synchronous machine technology is considered as an important technique to effectively control the shortcomings of renewable energy-based power electronics interfaces, providing backup inertia and regulating grid stability. Conventionally, the virtual synchronous machine with a large capacity is responsible for controlling the entire grid stability against renewable penetration. It is usually operated as a centralised control system. But what if virtual synchronous machines with small capacities are independently operated by their additional droop control schemes, and will they present better performance than the single virtual synchronous machine? This study proposes the multiple virtual synchronous machine system with different active power-frequency (P-f) droop characteristics to improve inertia support regarding frequency stability improvement. The comprehensive small-signal modelling of the multiple virtual synchronous machine unit is designed to include the additional P-f droop characteristics. Then, the dynamic characteristics (steady-state and transient responses) and static stability of the multiple virtual synchronous machines are compared with the single virtual synchronous machine at the same rated capacity in both eigenvalue/sensitivity-domain and time-domain analysis. The obtained results reveal that the system with the presence of several virtual synchronous machines is more stable than the system with single virtual synchronous machine, maintaining stable and secure system operation during the contingency.
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    Item type:Publication,
    Intelligence-Driven Grid-Forming Converter Control for Islanding Microgrids
    (2025-01-01) ; ;
    Mitani, Yasunori
    In modern microgrids (MGs) with high penetration of distributed energy resources (DERs), system reconfiguration occurs more frequently and becomes a significant issue. Fixed-parameter controllers may not handle these tasks effectively, as they lack the ability to adapt to the dynamic conditions in such environments. This paper proposes an intelligence-driven grid-forming (GFM) converter control method for islanding MGs using a robustness-guided neural network (RNN). To enhance the adaptability of the proposed method, traditional proportional-integral controllers in the GFM primary control loops are entirely replaced by the RNN. The RNN is trained by a robustness-guided strategy to replicate their robust behaviors. All the training stages are purely data-driven methods, which means that no system parameters are required for the controller design. Consequently, the proposed method is an intelligence-driven modelless GFM converter control. Compared with traditional methods, the simulation results in all testing scenarios show the clear benefits of the proposed method. The proposed method reduces overshoots by more than 71.24%, which keeps all damping ratios within the stable region and provides faster stabilization. In comparison to traditional methods, at the highest probability, the proposed method improves damping by over 14.7% and reduces the rates of change of frequency and voltage by over 59.97%. Additionally, the proposed method effectively suppresses the interactions between state variables caused by inverter-based resources, with frequencies ranging from 1.0 Hz to 1.422 Hz. Consequently, these frequencies contribute less than 19.79% To the observed transient responses.