The increasing interconnection of inverter-based resources (IBRs) with low short-circuit current has weakened grid strength, making phase-locked loops (PLLs) susceptible to instability due to accumulated phase-angle error under current limiting. This study defines such instability as IBR instability induced by reduced grid robustness and proposes a root-mean-square (RMS) model-based screening method. After fault clearance, the residual q-axis voltage observed by the PLL is treated as a disturbance signal and, using the PLL synchronization equations, is analyzed with a standard second-order formulation. The maximum phase angle at which synchronization fails is defined as θpeak, and the corresponding q-axis voltage is defined as Vq,crit. This value is then mapped to a screening metric Ppeak suitable for RMS-domain assessment. The proposed methodology is applied to the IEEE 39-bus test system: the stability boundary and Ppeak are obtained in Power System Simulator for Engineering (PSSE), and the results are validated through electromagnetic transient (EMT) simulations in PSCAD. The findings demonstrate that the RMS-based screening can effectively identify operating conditions that are prone to PLL instability in weak grids, providing a practical tool for planning and operation with high IBR penetration. This screening method supports power system planning for high-penetration inverter-based resources by identifying weak-grid locations that require EMT studies to ensure secure operation after grid faults.

This paper introduces the Local Renewable Management System (LRMS), developed to evaluate static stability and optimize renewable energy source (RES) output within local power systems in Korea. While the central Energy Management System (EMS) manages RES connected at the transmission level, LRMS specifically targets high-voltage distribution networks. By leveraging weather forecasts, LRMS accurately predicts RES generation, assesses system stability through real-time monitoring, and applies necessary control actions, including preventive voltage adjustments and renewable curtailment. A detailed case study from the Jeju power system demonstrates LRMS’s efficacy in enhancing renewable integration while ensuring system stability.

As power systems shift toward inverter-based resources (IBRs), maintaining stability depends on both total available inertia and system strength. This paper addresses frequency security by determining the required frequency response reserves (FRR) as an explicit function of the short-circuit capacity (SCC) at the renewable interconnection bus. For a fixed contingency, lower SCC at the connection point increases the required FRR and raises the secure operating level of inertia (SOLI); conversely, higher SCC reduces both for the same event. We show that, for a fixed contingency and nadir standard, lower local SCC at the renewable interconnection bus systematically increases both the required FRR and the SOLI. This SCC–FRR formulation enables system operators to set region-specific FRR targets and to assess the impact of renewable siting in weak versus strong areas without changing the underlying frequency-security standard. We substantiate this with a regional analysis on KEPCO’s system, using data-driven operating snapshots and dynamic frequency simulations for three areas with different SCC and renewable siting patterns. The results reveal local system strength differences across areas and demonstrate that relocating renewable connections alters FRR needs and shifts SOLI in proportion to local SCC. Jeonnam needs approximately 14–23% higher SOLI and 28–45% more FRR than other areas under the same nadir criterion.

This paper proposes a real-time oscillation monitoring framework based on an enhanced Geometric Feature Extraction (GFE) algorithm. The method utilizes high-resolution synchrophasor measurements from Phasor Measurement Units (PMUs) and employs a sliding window approach to identify oscillatory behavior in power systems. To improve detection robustness, the algorithm integrates signal-to-noise ratio (SNR) filtering and adaptive estimation of the Radius of Trajectory (RoT), which characterizes geometric patterns in reconstructed phase-space trajectories. A real-time alarming index is computed for each sample, and an oscillation alarm is triggered when the proportion of oscillatory samples within a window exceeds a predefined threshold. The proposed method was validated using actual PMU data recorded during a forced oscillation event caused by a Thyristor-Controlled Series Capacitor (TCSC) in the KEPCO power system. Experimental results demonstrate that the algorithm accurately captures the initiation, persistence, and attenuation of oscillatory behavior, offering both high detection sensitivity and low computational overhead suitable for real-time deployment.

Active power from renewable energy sources (RESs) is not suitable for long-distance transmission, and surplus generation can introduce stability concerns in high-voltage distribution networks. To address this problem, this study introduces the Local Renewable Management System (LRMS), a fully operational real-time framework deployed within the regional power system of the Korea Electric Power Corporation. The objective of the LRMS is to maximize the hosting capacity of RESs in high-voltage distribution grids while ensuring system stability. Unlike traditional centralized management systems, which regulate renewable generation primarily at the transmission level, the LRMS emphasizes localized control, enabling precise and adaptive responses to regional stability challenges arising from rapid RES penetration. Key processes include integration of real-time weather forecasts, RES output predictions, and stability assessment. Based on the calculated system non-synchronous penetration margin, the LRMS determines whether RES output can be increased or must be curtailed. Operational results from the Honam power system demonstrate the effectiveness and practical applicability of the LRMS in managing voltage profiles and system stability. An additional operational case study of the Jeju power system verifies the generalizability of the proposed system. Overall, this work presents a decentralized, data-driven solution for distribution-level RES integration, offering a scalable approach to meet carbon neutrality goals and increase RES penetration.

Abstract Managing the output of renewable energy sources considering their uncertainty and variability is crucial for resilience in power system operation. In addition, analyzing stability issues that may arise at the maximum output is important to ensure power system stability. Therefore, the authors propose a method for estimating the maximum non‐synchronous generation (Max NSG) of renewable energy based on the minimum inertia of the power system. The minimum inertia is determined through the correlation between the available and required quantity of inertia and governor resources, satisfying the frequency standards in a South Korean power system. The Max NSG of renewable energy sources at that system inertia level is estimated based on the derived minimum inertia. The proposed method was applied to 22,612 operation data extracted from the Korea energy management system (K‐EMS). The authors estimated a linear relationship between demand levels and Max NSG, ranging from 52.6 to 3.83 GW. The study shows that Max NSG, which is difficult to estimate in many power system operating conditions, can be estimated based on minimum inertia considering the frequency stability in South Korean power systems.

With the increase in inverter-based resources, maintaining system stability has made frequency maintenance criteria an important factor. In South Korea, there are two frequency maintenance criteria for N-1 and N-2 contingency faults, and consistency between these criteria is necessary to ensure the rational use of limited frequency response resources. This article proposes a method to verify the consistency of the criteria based on the minimum inertia in the system. The proposed methodology has the following salient features: i) developing a methodology to verify consistency between criteria based on minimum system inertia, ii) identifying the inconsistency in South Korea's existing frequency maintenance criteria and the need for their revision, iii) evaluating the impact of inconsistent frequency maintenance criteria on non-synchronous generation and system non-synchronous penetration. The methodology was validated on the IEEE 39 bus test system and applied to 7040 hourly operational data from the energy management system of the South Korean to verify the differences in criteria. The main result is that the two frequency maintenance criteria are inconsistent, require more frequency response resources in the N-1 criterion. The findings provide practical implications for system planners and operators, highlighting the need for frequency maintenance criteria revision in South Korea.

In low-inertia systems with a high penetration of renewable energy, the rotational kinetic energy and inertia constant are significant factors in determining frequency stability. The energy released owing to the frequency decrease during contingency represents a portion of the inertia that a synchronous machine possesses in the normal state. However, when securing inertia or planning additional resources to secure frequency stability, inertia in the normal state is analyzed as the standard rather than the amount of energy released during a fault. Therefore, in this paper, we define the actual energy emitted from a synchronous machine as Effective inertia. In order to evaluate Effective inertia in various operating conditions, we conducted a comprehensive review on approximately 24,627 cases from the years 2019, 2020, and 2021. As a result, in systems with low rotational kinetic energy, both low- and high-frequency nadirs were observed, indicating high uncertainty. However, Effective inertia presented a consistent trend regarding the energy release aligned with the minimum frequency. For instance, the rotational kinetic energy required to satisfy the frequency standard was 23 GWs, while the required Effective inertia was 858 MWs. We emphasize that securing inertia based on rotational kinetic energy includes additional imaginary energy that does not contribute to frequency, resulting in an energy requirement greater than that needed for Effective inertia. Therefore, in order to secure the frequency stability of the future system, the actual required energy amount based on Effective inertia will be presented and utilized in the inertia market and FFR (Fast Frequency Response) resource design.

The generation of inverter-based renewable energy affects system frequency and is limited by frequency criteria. In a power system with two or more criteria, it is important to understand whether the frequency criteria are appropriate because these should not differ in terms of renewable energy generation for consistent power operation. This study proposes a method to evaluate the frequency criteria applied to the system operation data by determining the minimum level of inertia required for the latter according to the effect of renewable energy generation. The minimum level of inertia can be determined as the minimum inertia value that satisfies the frequency criteria when inertia and frequency regulating reserve change with the operation of the generator. The minimum level of inertia was determined by conducting a frequency simulation by applying two frequency criteria in Korea. The proposed methodology has been applied to 7080 operation data, when two maximum output generators are operating more than 1400 MW simultaneously, out of 23003 time-based data extracted from the Energy Management System (EMS). Further, from the results, the minimum level of inertia for the N-1 frequency criterion was higher than the generator N-2 frequency criterion. This result indicates that the N-1 frequency criterion is more conservative in terms of the accommodation of renewable energy than the N-2 frequency criterion and that renewable energy will be limited by the N-1 frequency criterion. An important finding of this study is that the two frequency criteria in South Korea are applied differently in terms of the minimum level of inertia.& COPY; 2023 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

This paper introduces the concept of “Effective Inertia,” which refers to the kinetic energy contributed by synchronous generators up to a specific frequency threshold. Additionally, the notion of “Critical Effective Inertia” is proposed, representing the energy required until the lowest point of frequency. By quantifying these energy values, it becomes possible to determine the additional energy needed to maintain frequency stability. However, when evaluating effective inertia, it is crucial to account for Fast Frequency Response (FFR) mechanisms, such as HVDC, as they possess distinct dynamic characteristics. To demonstrate the application of this concept, a case study of the Jeju power system in South Korea is presented, focusing on the analysis of effective inertia in a low inertia system connected via HVDC.

Since the amount of power generated from inverter-based renewable energy affects the grid frequency, it is limited to maintain frequency reliability. In power system with two or more frequency standards, such as South Korea, the two standards should not be different for consistent system operation, so it is necessary to evaluate whether the frequency standards are appropriate for renewable energy accommodation. This paper proposes a methodology for evaluating the frequency standards by determining the minimum level of inertia required for the system operation considering the renewable energy generation. When inertia and frequency regulating reserve forces change as the operation of the generator changes, the minimal level of inertia can be calculated as the lowest inertia value that satisfies the frequency criteria. The minimal level of inertia was determined by conducting a frequency simulation by applying two frequency criteria in South Korea. The proposed methodology has been applied to 7080 operation time-based data extracted from Energy Management System. From the results, the minimal level of inertia for N-1 frequency criterion at the same situation was higher than the N-2 frequency criterion. The key finding of this study is that South Korea's two frequency criteria are applied differently based on the minimal level of inertia.

For power systems to manage a variety of renewable energy sources while securing system stability and reliability, more resources are required. However, due to the interaction of the frequency response resources, determining the appropriate resources for frequency stability is challenging. In the Jeju system, where two HVDCs control the frequency primarily, this paper suggests a closed-form frequency response prediction model that represents the response characteristics of a high-voltage direct current link (HVDC). The Jeju system has reached its limit as a result of the increased penetration of renewable energy, which has led to increasingly frequent renewable energy curtailments. To ensure the frequency stability of the Jeju power system, it is thought to be necessary to construct a flywheel-connected synchronous condenser. The impact of the inertia constant and capacity of a flywheel-connected synchronous condenser is examined using the proposed closed-form frequency response prediction model. Case studies are presented to demonstrate the feasibility of the proposed method. PSSE simulations are performed with the HVDC user-defined model which manufactured by General Electric (GE) and the Jeju Island power system in Korea. The suggested approach can be successfully applied to choose appropriate resources and plan resources for frequency stability.

In order to prepare measures for the stable operation of the power system to expand renewable energy, the renewable energy hosting capacity (HC) in the system shall be identified in advance. This paper proposes a methodology for predicting monthly HC based on factors affecting HC. It was found out that these factors are: Total generation, ratio of nuclear, coal, liquefied natural gas (LNG), and other power generations. A prediction model was developed using multiple linear regression by integrating and separating data of elements from weekend data. A comparison of the determination coefficients showed that the models incorporating weekend data exhibited the best accuracy. In conclusion, the proposed model has the characteristics of predicting various HCs simply and quickly with five factors.

In order to reduce greenhouse gas emissions, the connection of renewable energy to power system is increasing. Renewable energy such as wind power and photovoltaic are inverter-based resources (IBRs) that provide limited short-circuit current unlike synchronous generators, and the limited short-circuit current adversely affects voltage after disturbance. Describes Short Circuit Ratio(SCR), a system strength evaluation index used in power systems when connecting inverter-based resources, and Weighted Short Circuit Ratio(WSCR) and Composite Short Circuit Ratio(CSCR), system strength evaluation indexes considering the interaction between inverter-based resources caused by Phased-Locked Loop(PLL) control characteristics is analyzed.

Given the rapid increase in inverter-based distributed generators (IBDGs), their response and subsequent impacts on power system stability during abnormal power system conditions are becoming important. Recent events have shown that an unexpected loss of IBDGs triggered by their outdated frequency ride-through (FRT) capability can occur, which in turn can lead to a power system frequency below the secure operation region. As FRT characteristics of IBDGs are dependent on their time of installation and capability to update FRT parameters, IBDGs with different ride-through characteristics are mixed within the power system. In this study, the potential impacts of FRT capabilities of IBDGs with legacy inverters have been investigated. The analysis was conducted considering the penetration level of IBDGs and complying with FRT characteristics. Furthermore, the required amount of fast frequency response resources, which are generally provided by battery energy storage systems, was evaluated along with the secure operating envelope that can aid in future power system planning. Case studies on modified New England 10-machine test system and Korean power system were conducted to validate the effectiveness of the analysis. (c) 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CCBY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

There is a global focus on adding renewable energy sources to the mix of energy supplies. In this study, the grid connections for large-scale offshore wind farms in areas that have high penetration of renewable energy sources were examined. System strength evaluation considering the interaction of wind farms and inverter-based resources (IBRs) was performed; the fault current was then analyzed to determine their contribution to the total fault current at a bus level. These studies revealed that the interaction between offshore wind farms and IBRs may make the power system weaker, and it is possible that fault current contributions from offshore wind farms can violate the capacity limit of existing circuit breakers. The results of steady-state analysis were verified through case studies focused on the southwest area of the Korea Electric Power Corporation (KEPCO) system where large-scale offshore wind farms are planned to be established and connected. Power system planners will benefit from the results of this study with a better understanding of the factors to consider when integrating large-scale wind farms in areas with high penetration of renewables.

In this paper, we develop a 'Local Renewable Management System (LRMS), to predict, monitor, and control the renewable energy sources (RES) of local power system. The LRMS conducts on-line stability assessment while gradually increasing the generation of RES and decreasing the power flow of inter-connection line to determine the maximum capacity of the RES. This paper introduces the structure of LRMS to assess the local power system stability. The algorithmic structure of LRMS is described and the stability relieving process of LRMS such as preventive control and curtailment process is depicted. Finally, the case study is conducted through Jeju power system with an analysis and observation.

This paper proposes a method to mitigate subsynchronous torsional interaction detected during power system operation. This innovative method employs the delay reconstruction of the damping controller of a thyristor-controlled series compensator. This addresses the need to detect and manage stability and electromagnetic transients in power systems caused by the increasing use of fast-response power electronics. Previously, severe oscillation conditions could be avoided via analysis of the subsynchronous torsional interaction scenarios during the planning stage, enabling the suppression of oscillations. However, planning, modeling, and analysis for various scenarios becomes more difficult as the complexity of the power system increases, owing to the use of renewable energy and the incorporation of topology changes. Therefore, interest in measurement data-based real-time oscillation analysis has increased. The first step of the mitigation strategy proposed herein reconstructs nonlinear time-series data to detect subsynchronous torsional interaction in real time and generate alert signals. The second step of the strategy is that the controller mitigates oscillations by controlling the firing angle using the geometric feature extraction method. In this paper, the relaxation of the frequency oscillation in the subsynchronous region of about 22 Hz and about 18 Hz was verified through two simulation cases.

System strength is an important concept in the integration of renewable energy sources (RESs). However, evaluating system strength is becoming more ambiguous due to the interaction of RESs. This paper proposes a novel scheme to define the actual interaction boundaries of RESs using the power flow tracing strategy. Based on the proposed method, the interaction boundaries of RESs were identified at the southwest side of Korea Electric Power Corporation (KEPCO) systems. The test results show that the proposed approach always provides the identical interaction boundaries of RESs in KEPCO systems, compared to the Electric Reliability Council of Texas (ERCOT) method. The consistent boundaries could be a guideline for power-system planners to assess more accurate system strength, considering the actual interactions of the RESs.

As the penetration level of renewable energy sources (RESs) increases, the decrease in the system inertia and spinning reserves will be one of the major challenges for the secure operation of power systems. Recently, in order to secure power system frequency within the limit defined in the grid code, accurate analysis on the frequency responsive reserves is getting important. In this study, method of evaluating the minimum level of inertia along with the required reserves to secure system frequency is developed. Furthermore, maximum allowable penetration level of RESs is analyzed in order to secure frequency after a sudden loss of a single generator unit. And with the evaluated minimum inertia for the secure frequency, this study shows the amount of the increased generation and the system frequency response in the time frame after a single generator or two generator units are tripped off. In the developed method, increase in RES penetration is illustrated as a negative load while considering the merit order of conventional generators. A case study is conducted on the future Korean power system of 2024.