The low and variable inertia due to the integration of large-scale wind generation poses severe challenges to the frequency control of the power grid. In this study, a novel model predictive control ...(MPC)-based load frequency controller (LFC), which can adapt to the changes in system inertia, is proposed to improve the frequency control effect. First, the inertia estimation scheme based on measurements is designed. Then, the state-space model, which is the key that determines the control effect of MPC, is corrected in time based on the estimated inertia. The proposed method in this study can avoid the problem of MPC-based LFC failure caused by inaccurate model parameters. The performance of the proposed strategy is demonstrated in two scenarios, i.e. wind power fluctuation and load multi-step, using a two-area interconnected power system with time-variant inertia.
This paper is dealing with two split extensions of the form 2 8 : A 9 . We refer to these two groups by G ¯ 1 and G ¯ 2 . For G ¯ 1 , the 8-dimensional GF(2)-module is in fact the deleted permutation ...module for A 9 . We firstly determine the conjugacy classes of G ¯ 1 and G ¯ 2 using the coset analysis technique. The structures of inertia factor groups were determined for the two extensions. The inertia factor groups of G ¯ 1 are A 9 , A 8 , S 7 , ( A 6 × 3 ) : 2 and ( A 5 × A 4 ) : 2 , while the inertia factor groups of G ¯ 2 are A 9 , P S L ( 2 , 8 ) : 3 and 2 3 : G L ( 3 , 2 ) . We then determine the Fischer matrices for these two groups and apply the Clifford–Fischer theory to compute the ordinary character tables of G ¯ 1 and G ¯ 2 . The Fischer matrices of G ¯ 1 and G ¯ 2 are all integer valued, with sizes ranging from 1 to 9 and from 1 to 4 respectively. The full character tables of G ¯ 1 and G ¯ 2 are 84 × 84 and 40 × 40 complex valued matrices respectively.
•A comprehensive review of inertia estimation techniques is provided for SGs, including the model-based and measurement-based approaches.•This is the first attempt to propose new potential algorithms ...for the estimation of the inertia from different VIE-based CIGs according to their various control characteristics.•New insights for future work on quantifying power system inertia considering CIGs and their potential applications are extensively discussed.
Understanding and quantifying the inertia of power systems with the integration of converter-interfaced generation (CIG) plays an essential role in the safe transition to a future low-inertia scenario. This paper provides a comprehensive summary of inertia definitions for both synchronous generators and CIGs as well as their corresponding estimation methods. In particular, the estimation methods are categorized as model-based and measurement-based approaches considering both small and large disturbances. The advantages and disadvantages of different methods are carefully discussed. This paper also offers for the first time a framework to quantify the virtual inertia of CIGs at the component and aggregation levels, an open problem in the literature. Finally, future directions for inertia estimation are identified and discussed. This significantly benefits the design of appropriate control and protection schemes in achieving a more reliable, secure, and resilient power system.
By integrating a significant amount of renewable energy sources such as wind power and photovoltaic, the power system is gradually evolving into a low-inertia power system. The reduction in the ...proportion of synchronous generators has resulted in a diminished ability to provide inertia support to the power system, consequently leading to increasingly severe challenges in maintaining frequency stability. To address this issue and enhance the inertia of the power system, several strategies for virtual inertia control have been developed. These strategies have the potential to reshape the output characteristics of power-electronics-interfaced renewable energy sources and battery storage systems. Following the wide usage of virtual inertia control, the inertia estimation has emerged as an urgent concern in practical applications for grid operators. Hence, a comprehensive and critical review of inertia estimation has become imperative. The primary objective of this survey research is to provide an overview of virtual inertia control strategies. Additionally, this study summarizes inertia estimation methods in both individual converter and regional power system according to different disturbance signals. Furthermore, various analysis methods for evaluating the level of system inertia are discussed. Furthermore, the configuration of virtual inertia for power system is discussed thoroughly. Finally, future research trends on the virtual inertia estimation of converter and the configuration of virtual inertia of the power system are discussed.
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•The power system has deeply mutated to renewable-energy-dominated power system.•Multiple forms of virtual inertia have been studied to enhance system-frequency stability.•Inertia estimation for a single converter is essential for the renewable power system.
With the increasing integration of renewable energy resources into power grids, system inertia is decreasing considerably. This trend poses major challenges to transmission system operators and ...requires a comprehensive understanding of inertia-related information to formulate effective strategies that ensure power system frequency stability. In this study, an inertia security evaluation methodology is proposed from a frequency stability perspective, including its definition, quantitative assessment, and application. First, the definition and mathematical underpinnings of the inertia security region (ISR) are introduced. Then an evaluation method for the ISR is established, considering various frequency stability control strategies based on the size of the disturbance. Two quantitative indices, the inertia security ratio and inertia adjustable capability, are introduced to assist grid operators in determining the system inertia security status and assessing the inertia adjustability capability. Furthermore, for inertia deficits, a sensitivity-based inertia allocation approach is proposed for credible contingencies. Finally, the efficacy of the proposed ISR approach is validated using case studies on a modified 39-bus system and a practical large-scale power grid in China.
The effects of photon inertia on the determination of its trajectory were verified and the representation of a displacement mass characterized by the flow of the number of wavefronts and the ...decomposition of photon inertia into parts associated with translation and rotation motions was considered. It was found that with the relativistic increase of the photon's resistance to change its directional properties, it inhibits the relativistic trajectory of the second torque, so called Minkowski torque, in an angular range of incidence. After synchronizations, in the OAM inversions, there are reductions of the inertia associated to the translational part that assumes classical predominance, where the relativistic trajectory is allowed while the photon offers less resistance to changes in its directional properties. The classical-relativistic variability of the photon inertia characterizes the classical or relativistic profile of the energy distribution in forms of motion, where adjustments of the rotational and translational parts can be performed as a function of the refractive index rate, temperature and angle of incidence. It was found that with increasing temperature of the refringent medium, the synchronizations displacement in the sense of the normal incidence. A specific vacuum temperature for the refringent medium was characterized, where the photon exhibits a classical-relativistic synchronization under all angles of incidence, characteristic of its immaterial state in vacuum.
Recent studies show that the vigorous seasonal cycle of the mixed layer modulates upper ocean submesoscale turbulence. Here we provide model‐based evidence that the seasonally changing upper ocean ...stratification in the Kuroshio Extension also modulates submesoscale (here 10–100 km) inertia‐gravity waves. Summertime restratification weakens submesoscale turbulence but enhances inertia‐gravity waves near the surface. Thus, submesoscale turbulence and inertia‐gravity waves undergo vigorous out‐of‐phase seasonal cycles. These results imply a strong seasonal modulation of the accuracy of geostrophic velocity diagnosed from submesoscale sea surface height delivered by the Surface Water and Ocean Topography satellite mission.
Key Points
Upper ocean submesoscale (here 10‐100 km) turbulence and inertia‐gravity waves undergo strong seasonal cycles that are out of phase
Submesoscale turbulence dominates the horizontal velocity and sea surface height variability in late winter/early spring
Submesoscale inertia‐gravity waves dominate the horizontal velocity and sea surface height variability in late summer/early fall
Wind turbines can have inertia characteristics similar to synchronous generators through virtual inertia control, which helps to provide the inertia support for the system. However, there is the ...problem of how to coordinate the allocation of virtual inertia among wind turbines. In response to this problem, this paper first analyzes the inertia response capabilities of wind turbines and puts forward an evaluation index that quantifies the inertia response capability of wind turbines. The inertia response capability of a wind farm is evaluated at the entire system level. Based on the evaluation index, the virtual inertia coordinated allocation method considers the system inertia demand and the inertia response capabilities of the wind turbines. It is proposed to release the inertia response capability of each wind turbine while avoiding an excessive release of kinetic energy and bring a second impact by wind turbines’ exiting operation. Finally, the effectiveness of the proposed method is verified by a simulation case study.
Several studies show that grid-integrated renewable energy (RE) sources have the potential to replace conventional synchronous generators in the network. This means the grid will experience low ...conventional inertia that is currently provided by synchronous generators. Low, unpredictable and time-changing inertia in the power system, as a result of high penetration of non-synchronous RE sources, can cause rapid frequency oscillations. The rapid and unpredictable frequency oscillations are the major source of stability challenges in the power system. Therefore, this research presents a comprehensive literature survey on the role of inertia for grid flexibility under high penetration of non-synchronous RE sources to the power system. As inertia is becoming a time-changing quantity, inertia estimation techniques have been gaining popularity as solutions to stability challenges faced by the power system. Related to time-changing inertia, the following are discussed in this survey research. First, synthetic inertia provision in the network and the need for inertia estimation are intensively discussed. Second, the importance of prior knowledge of the system inertia, which will help operators to apply suitable control strategies to mitigate stability challenges, is also addressed. Third, the significance of co-existence, coordination and optimization of both conventional synchronous generator's inertia and synthetic inertia, as a key feature towards reliable and flexible grid in low inertia environment, are also emphasized. Finally, technical challenges, key issues, and further research needs are highlighted.
•Discussed challenges of low and time-varying inertia on the grid's frequency stability.•Explained significance of synthetic inertia to the grid's frequency stability.•Reviewed inertia estimation techniques in power systems extensively.•Highlighted the need for coordination and optimization of inertia for grid flexibility.•Emphasized the need for inertia monitoring for planning and operation of the grid.
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