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.
• The proposed method derives the minimum inertia based on the correlation between the available and required capacity of inertia and governor resources, considering the frequency standard.
• The authors estimate Max NSG at the system level based on the minimum inertia.
• The authors estimate Max NSG by reviewing actual data that reflect various system operating conditions.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The global increase in the use of solar photovoltaics and wind turbines has led to a rapid increase in the penetration level of inverter‐based distributed generators (IBDGs). Until recently, the ...operation modes of IBDGs under abnormal power system conditions were not a major concern owing to the small number of IBDGs used in power systems. However, several events have indicated that the momentary cessation (MC) mode of an IBDG can eventually deteriorate the stability of power systems. Among the various parameters that define the MC mode, the direct impact of the MC recovery ramp rate on the transient stability of the power system has been addressed by computing the stability margin based on a single machine equivalent method. Furthermore, this paper introduces the critical momentary cessation recovery ramp rate for a specific system, which can be used as an important index in the planning of an IBDG installation. Case studies on modified IEEE 39 bus system and Korean power system were conducted to validate the effectiveness of the proposed method.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Renewable energy curtailment often occurs to accommodate large amounts of renewable energy sources in power systems while maintaining system stability and reliability. Widely known methods, such as ...new transmission line construction, the introduction of demand-side resources, and the reduction of conventional generator output, can minimize the occurrence of curtailment; however, there are difficulties in introducing them because of social and economic problems. For these problems, the Jeju power system adopted a battery energy storage system (BESS) resource to mitigate the curtailment and secure frequency stability with the high penetration of renewable energy. The small-size Jeju island power system is operated with reliability must-run (RMR) units and high-voltage direct current (HVDC) lines connected to the mainland. Since the number of RMR units contributes to frequency stability by providing inertia, reducing the number of operating units for curtailment mitigation is difficult. Therefore, in this paper, based on the current “Carbon-Free island” policy and operation plan of the Jeju power system, we proposed a BESS for reducing the number of RMR units, observe the effect of reducing curtailment using the BESS, and suggest a practical operation plan to reduce the number of RMR units under conditions that secure frequency stability.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The responses of an inverter-based distributed generator (IBDG) to abnormal voltage and frequency are different from those of a conventional generator owing to the difference in the operating modes. ...In particular, the momentary cessation (MC) mode deteriorates the transient stability of normal power systems by ceasing to provide active and reactive power to the grid. However, in a high-generation area, where a significant amount of generation is concentrated and where transient instability exists under a contingency, MC operation is conducive to the transient stability because the electrical output of critical generators increases to cover the local loads under this condition. This effect can cause frequency instability if a sizeable portion of the IBDG output is lost owing to the operating modes. To ensure transient and frequency stability, this study analyzed the effects of operating modes and generator tripping on the high-generation area. A method for determining the capacity limit of the IBDGs in the high-generation area was then developed to ensure power system stability. The effectiveness and feasibility of the proposed method were verified by conducting a case study on the Korean power system.
The inertia of a power grid plays a significant role in maintaining the stability of a system. If the inertia is large enough, stable operating conditions can be maintained during small scale events. ...As the percentage of power supplied by renewable energy sources increases, the value of inertia in a system will decrease. Therefore, it has become necessary to accurately estimate the inertia in the system. Traditional methods of estimating the inertia make use of fault conditions to allow for the dynamics in the system to be accurately observable. However, this is not optimal as fault conditions are infrequent and undesirable. The method detailed makes use of modal information which can be obtained via synchrophasor measurements to estimate the inertia during steady-state conditions. The results show that while the estimation is not accurate for individual buses, the values calculated for regional and system inertias are more accurate.
In this study, a new algorithm dealing with time-varying modes for determining and tracing multiple frequency oscillations in power systems is proposed. Multiple modes or resonance of forced and ...natural oscillations can have severe effects on a power system. Therefore, it is crucial to recognize the dominant natural and forced oscillations because the oscillation mode possesses time-varying features that depend on the system operating conditions or changes in the parameters. The salient features of the proposed algorithm include the use of a time-series-based approach to recognize undesired modes (including multiple oscillations over a wide frequency range), tracing time-varying modes as the power system operating condition changes, and effectively determining and applying the oscillation features before implementing the corresponding control measures in the power system. In this study, multiple frequency oscillation scenarios for the test system and practical measurement data for a recent incident that occurred in Korea Electric Power Corporation (KEPCO) system are discussed. Therefore, the proposed algorithm can be practically applied in wide-area monitoring systems, not only for a single forced oscillation or local mode detection but also for system-wide inter-area mode recognition.
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