Dynamic VAR Research Articles

Optimal configuration of dynamic VAR compensators considering uncertainty and correlation

AbstractThe transient voltage stability of modern power systems is challenged by the increasing uncertainty on source‐load dual sides. To cope with it, a robust optimal configuration method for dynamic VAR compensators (DVCs) is proposed. First, a series of power‐flow scenarios are generated with uncertainty and correlation considered, where nonparametric kernel density estimation is used to predict the marginal distribution of wind speeds and combined Copula function is employed to characterize correlations between nearby wind farms. Then, the variation‐of‐information indicator is introduced to assess the similarity among power‐flow (PF) scenarios, and representative PF (RPF) scenarios are screened with the help of Spectral clustering algorithm. Finally, locating and sizing of DVCs for RPF scenarios are achieved. By synthesizing the compensation schemes for RPF scenarios, the robust configuration scheme is suggested. Simulation studies in the modified New England 10‐machine 39‐bus system show the proposed method can ensure transient voltage security of the studied power system under source‐load uncertainty.

Bitcoin's Effect on Selected Crypto Assets: Quantitative Evidence

The main objective of the study is to systematically investigate the effects of Bitcoin on specific crypto assets. In this context, a sample of 135 observations between 2020W01 and 2022W33 for seven crypto assets with the highest value in the financial markets, including Ethereum, Tether, USD Coin, BNB, XRP, and Cardano, has been included in the study sample. These crypto assets, along with Bitcoin, constitute almost 95% of the total crypto asset portfolio. This situation increases the importance of representing a broad universe in the study and contributes to the academic literature. To examine the effects of Bitcoin on the selected crypto assets, a Multivariate Dynamic VAR Model has been used. The model assumes causality among variables. Variables that do not meet this assumption have been excluded from the study sample. The results of the study demonstrate that Bitcoin exhibits significant and one-way effects on all cryptocurrencies. However, the impact of other crypto assets on Bitcoin has been negligible. In this context, it is emphasized that investment decisions obtained from two-way evaluations may be risky and misleading. In order to reduce investment risks for crypto assets to more acceptable levels, the use of comprehensive analysis methods is recommended.

Nonlinear and threshold effect of corporate social responsibility on bank performance

ABSTRACT This study examines the non-linear and threshold effects of corporate social responsibility (CSR) on bank performance. For empirical analysis, this study has used data from 30 Bangladeshi and 26 Indian banks from 2015 to 2021. The non-linear dynamic GMM and panel VAR model results suggest a U-shaped relationship. The threshold regression suggests that there is tipping point for earning to earnings assets, Tobin’s-Q, and return on equity for Bangladeshi and Indian banks. Additionally, this study shows the negative (positive) relationship exists between CSR expenditure and bank performance before (after) the tipping point. Findings reveal that lower CSR does not have any marginal benefit but rather increase cost, and optimal CSR increase the bank's performance. Therefore, policymakers and bank management should invest considering the threshold level to get a positive outcome from CSR.

Hybrid model-data-driven dynamic VAR planning for wind-penetrated power system using spectral surrogate techniques

The increasing wind power penetration and proliferation of induction motor loads, of which dynamic impact cannot be revealed through steady-state analysis, bring challenges to the short-term voltage stability of modern power systems. This study proposes a hybrid model-data-driven approach for dynamic VAR source planning to enhance the short-term voltage stability of wind-penetrated power systems to reduce the computation burden of electro-mechanical transient models. Firstly, the theoretical background of Stochastic Spectral Embedding (SSE) is introduced. Then, a surrogate model for the electromechanical transient model is established using SSE following efficient expansion coefficient calculation and a designed partition strategy for the studied problem. Furthermore, a hybrid model-data-driven VAR deployment optimization model is established with 3 objectives, which is solved by a dual-population-based evolutionary algorithm (DPEA). The accuracy and effectiveness of the model are verified on a modified New England 39-bus system. Simulation results prove that the computational cost is reduced significantly in comparison with conventional model-based method without a compromise in accuracy and the proposed method is also more accurate than methods based on other surrogate models. The proposed SSE-based model can be applied to other power system analysis with electro-mechanical transient models to alleviate the computational cost.

Multi-objective dynamic VAR planning against fault-induced delayed voltage recovery using heuristic optimization

Multi-objective dynamic VAR planning against fault-induced delayed voltage recovery using heuristic optimization

International emigration and economic complexity: Evidence from the dynamic GMM panel VAR approach

For over a decade, developing nations have used foreign direct investment and trade to access advanced economies’ technology and knowledge. However, the role of emigrants in promoting the productive capacity of their home countries through the diffusion of knowledge and novel technologies has been relatively overlooked. The present study investigated the relationship between emigration stock and productive knowledge embedded in their origin economy, as measured by the Economic Complexity Index (ECI). The study applied a GMM Panel Vector Autoregressive (PVAR) technique to 86 non-high-income countries between 1995 and 2020. In principle, the PVAR model findings indicated that international emigrants promoted the level of technology and knowledge in their home countries. Further causality analyses revealed that within all countries, there was unidirectional causality from emigration to the ECI. However, a bidirectional relationship existed between the two variables in countries with low education levels. Developing countries should consider the opportunities emigrants offer when planning their development strategies.

A Data-Driven Trajectory Approach for Dynamic VAr Support in Renewable Rich Power Grid

A Data-Driven Trajectory Approach for Dynamic VAr Support in Renewable Rich Power Grid

Parameter Optimization for Var Planning of Systems With High Penetration of Wind Power: An Adaptive Equivalent Reduction Method

Voltage-related issues such as dramatic voltage fluctuation, lack of Var reserves, become more prominent in high wind power penetration (HWPP) system, leading to increasing of large-scale cascading trip risks within 100-200ms. During the cascading process, fast dynamic Var support, which is strongly related to internal parameters of Var devices, is quite crucial for HWPP system security. If device parameters optimization is also considered in the Var planning, it will be more promising to achieve less investment cost and guarantee transient security for HWPP system. However, the complex control elements and numerous internal parameters optimization cause a huge computational burden of planning issues. Therefore, this paper proposes an adaptively parameter order equivalent reduced optimization (APO-ERO) approach to efficiently and accurately solve the Var planning problem with parameter allocation. First, the original high-order Var device model is adaptively reduced to an optimal low-order model that minimizes the reduced order error. Next, an equivalent low-order optimization model in the upper layer and an inverse mapping parameter allocation model in the lower layer are established to relieve the computational burden. Finally, the two different test systems with HWPP verify that the proposed method can improve computational efficiency on the premise of guaranteeing accuracy.

Militarization, globalization and liberal democracy: a nexus?

PurposeUsing composite indices, the paper examines the nexus between militarization, globalization and liberal democracy. The democratic peace theory, the conflict inhibiting effects of international trade – a key and dominant facet of globalization – and the democracy promoting globalization hypothesis form the theoretical underpinnings of the empirical investigation.Design/methodology/approachTo probe into the issue at hand, the paper adopts a dynamic panel VAR estimation procedure. Given the usual data constraints, the sample consists of 113 countries, and the estimations span the period 1995–2019.FindingsThe findings from the dynamic panel VAR estimations suggest the presence of a negative and statistically significant nexus between the level of globalization and the level of militarization. No statistically traceable nexus between globalization and liberal democracy was found.Research limitations/implicationsThe findings offer empirical support to the hypothesis that the strong links of interdependence shaped by globalization reduce the need for military preparedness. The results lead to a tentative inference in favor of the doux commerce thesis. Nonetheless, given that the estimations span a historically specific period – the entire post-bipolar era – the inferences that stem from the findings should be treated with caution.Originality/valueTo the best of the authors’ knowledge, the composite indices Bonn International Centre for Conflict Studies (BICC) militarization index, the globalization index of the Swiss Economic Institute (Konjunkturforschungsstelle) (KOF), LibDem, polyarchy have not hitherto been jointly used in previous studies to examine the nexus between militarization, globalization and liberal democracy.

Dynamic Reactive Power Optimization Configuration of New Energy Power Station Based on Fault Limit Removal Time

The large-scale construction of long-distance, high voltage level transmission projects and sustained load demand increase negatively influence transient voltage stability. A certain amount of dynamic Var compensation at the receiving end of the power grid can significantly improve the stability. Most new energy power plants, such as wind power, and photovoltaic generation, have installed dynamic Var compensation devices. The potential for safety and stability control should be fully exploited. In this paper, it is concluded that the critical fault clearing time is the main index to measure the transient voltage stability of the system, and the critical fault clearing time has been extended by allocating dynamic Var compensation. According to these conclusions, a method for optimal allocation of dynamic Var compensation to improve critical fault clearing time is proposed. The method has determined the optimal capacity and the installation point. The effectiveness of the proposed method is illustrated through simulations on the actual power grid.

Modeling dynamic VaR and CVaR of cryptocurrency returns with alpha-stable innovations

We employ alpha-stable distribution to dynamically compute risk exposure measures for the five most traded cryptocurrencies. Returns are jointly modeled with an ARMA-GARCH approach for their conditional mean and variance processes with alpha-stable innovations. We use the MLE method to estimate the parameters of this distribution, along with those of conditional mean and variance. Our results show that the dynamic approach is superior to the static method. We also find out that these risk measures of five cryptocurrencies do not offer the same pattern of behavior across subperiods (i.e., pre-, during- and post-COVID pandemic).

Optimal selection of single tuned passive filters to enhance post‐fault voltage recovery and power quality in a renewable integrated microgrid

AbstractThe harmonic currents produced by nonlinear loads and renewable energy sources (RES) like PV and wind energy have had a growing impact on industrial distribution networks in recent times. Along with harmonic distortions, lack of adequate reactive power support in a heavily loaded renewable‐rich industrial network has made the operation vulnerable to fault‐induced delayed voltage recovery (FIDVR). Due to poor post‐fault voltage recovery, an industrial microgrid is exposed to cascading loss of distributed generators (DGs). Dynamic var sources are being used to prevent cascade tripping. However, they may result in deterioration of the network's THD scenarios. Single tuned passive filters are widely used to suppress harmonic contents. The goal of this work is to design filters so that these become capable to lower overall harmonic distortion while also minimizing the risk of blackouts caused by inadequate post‐fault voltage recovery. To determine the allocation and rating of single tuned passive filters in a renewable‐penetrated industrial microgrid, an optimization model is developed. To show the feasibility and efficacy of the proposed formulation, simulations are performed on a modified IEEE 43 bus system. The findings suggest that the proposed design methodology produces effective solutions to minimize the necessity of additional reactive power sources.

Adopting Dynamic VAR Compensators to Mitigate PV Impacts on Unbalanced Distribution Systems

Adopting Dynamic VAR Compensators to Mitigate PV Impacts on Unbalanced Distribution Systems

Reactive power compensation using STATCOM in a PV grid connected system with a modified MPPT method

Commonly Static Synchronous Compensators (STATCOMs) are employed extensively as voltage regulators and VAR compensators in transmission networks in power systems. This research proposes the integration of STATCOMs in distribution networks, particularly in PV grid-connected systems that use distributed energy resources to reduce active and reactive power demand from the grid by supplying variable reactive power from an alternative supply which adapts to the load demand. This decreases the dependence on the utility power supply and promotes the integration of STATCOMs with renewables. Complete case studies between the differences in application of a fixed reactive power compensating condenser and STATCOM for dynamic VAR compensation to loads connected at the point of common coupling in a grid connected Photo-Voltaic (PV) system is presented. The scope of this research is to examine the behavior of dynamic loads, such as an induction motor, at steady state operation when the reactive power demand from the supply increases, as well as the effect of this demand variation on the network that supplies such loads. Complete system modeling and analysis for both scenarios, the fixed reactive power compensator and the STATCOM, supplying various load demands, have been developed. The simulation is based on a 100-kW rated PV grid-connected system to simulate behavior and performance of such study. Adaptive Neuro Fuzzy Inference System with Particle Swarm Optimization was used to extract the maximum power point of the PV array proceeded by a sliding mode controller. MATLAB/ Simulink was developed for modelling and analysis. Various load dynamics with varying solar irradiance and increasing reactive power demand of the associated load were simulated to evaluate various challenges and disturbances on the power supply.

Examining the role of renewable energy on the foreign exchange rate of the OECD economies with dynamic panel GMM and Bayesian VAR model

Examining the role of renewable energy on the foreign exchange rate of the OECD economies with dynamic panel GMM and Bayesian VAR model

Fast Var Margin Evaluation of High Wind Penetration Power Systems: An Objective-Oriented Dimensionality Reduction Approximation Approach

A high proportion of wind power systems with correct as set weak network connections may suffer from cascading trip faults due to the lack of conventional power plants and voltage/var support, which brings about great challenges to secure wind farm operations. To accurately and efficiently evaluate the dynamic var margin for an online field application within large-scale integrated wind areas, the transient dynamic voltage processes of hundreds or thousands of wind turbines must all be considered due to the dramatic interior voltage fluctuation effect of wind units, which brings a heavy computational burden for solving the TSCOPF problem. Therefore, to address these large-scale challenges, this paper proposes an objective-oriented approximation dimensionality reduction equivalent (OOA-DRE) approach, which accurately transforms the high-dimensional differential system to a low-dimensional system with few differential equations and low-dimensional algebraic equations for the wind unit with the maximum electrical distance value. Meanwhile, this paper uses the Levenberg-Marquardt method to obtain the global pre-evaluation error, so that the evaluation error reaches the minimum value. Finally, an actual wind power system verifies that the calculation time is reduced by approximately 2/3 compared with the original model on the premise of ensuring accuracy for large-scale systems.

PENGARUH TINGKAT KEMISKINAN DAN ANGKA PUTUS SEKOLAH TERHADAP PEKERJA ANAK DI INDONESIA

This study examined the influence of Poverty Rate and Dropout Rates on Child Labor in Indonesia. This study used secondary data obtained from the publications of the Central Bureau of Statistics of Indonesia for 21 years (1999-2019). To achieve the results of this study, a dynamic VAR model analysis using the Eviews 9 program was used. The results indicated that poverty rate had a positive and significant effect on child labor in Indonesia and the dropout rate did not have a significant effect on child labor in Indonesia. The researcher hopes that the government can increase family economic empowerment, expand educational opportunities for child workers and their families, provide more employment opportunities to reduce poverty

Coordination of D-STATCOM & SVC for Dynamic VAR Compensation and Voltage Stabilization of an AC Grid Interconnected to a DC Microgrid

This article presents a new collaborative control method based on expert decision, proposed for the combined system of an ac grid with a low THD thyristorized static var compensator (SVC), interconnected to a dc microgrid through a distribution static compensator (D-STATCOM) that also works as a bidirectional power converter. The combination of large rating SVC and a low rating D-STATCOM functions as a hybrid compensator for the ac distribution grid. In the combined mode of operation, the D-STATCOM mitigates voltage fluctuations and compensates initial var demands, while the SVC caters to the base var requirements. The D-STATCOM has also been used for integration of a dc microgrid to the utility grid, permitting exchange of power between the grids and thereby reducing voltage fluctuations of both the systems. The proposed collaborative control method based on expert decision can extract the full advantages of the respective subsystems as per demand of the operating condition. This combined system complies with the relevant harmonic standards and can effectively correct system power factor, stabilize bus voltage, and mitigate voltage flicker under fluctuating load conditions. Theoretical analyses with simulation results as well as experimental results show that the proposed system can meet the requirement of continuous dynamic reactive power compensation and voltage stabilization with low cost, high reliability, and large capacity.

Board Inclusion in Financial Reporting and Dividend Policy: Evidence from Static and Dynamic Panel VAR Models

The study explored how board inclusion in financial reporting affects the dividend policy in Nigeria. The study was conducted within the context of deposit money banks (DMBs) and data were gathered from the financial statement of listed DMBs in Nigeria for ten years spanning from 2008 to 2017. The study employed static and dynamic panel VAR technique. The result showed that dividend per share can predicts frequency of the board meeting, the frequency of board meeting can predicts board compliance to banks' rules and regulation in the future and board compliance to banks' rules and regulation can predict dividend per share. The study concluded that board inclusion in financial reporting on dividend policy exerts long-run and short run negative effect on dividend policy. In view of this study recommended that the board inclusion in financial reporting should aim at discouraging manipulative accounting tendencies and enhance true fare of financial position of the banks with the goal of improving or maximising dividend policy represented by the amount of cash pay-out as dividend to shareholders as a form of reward for their investments.

Dynamic reactive power characteristic analysis of inverters under the commutation failure faults in HVDC systems

In the traditional high voltage direct current (HVDC) systems, commutation failure (CF) fault is one major challenge, and the transient var characteristic of the inverter station is an essential factor in the counter measures against CF fault. Based on the detailed switching process of valves during CF, the var demand characteristic is analysed. From the key factors during the recovery of CF, the dynamic var demand characteristic is investigated. It is shown that, the dc side of converter is short-circuited and the ac side can be regarded as open-circuit. Moreover, the var demand of inverter station is mainly influenced by the changing ratio of dc current and commutating voltage. At last, the case studies verify the validity of the reactive power characteristics of the inverter station proposed in this paper.