VAR System Research Articles

Rough Fuzzy Control of SVC for Power System Stability Enhancement

This paper presents a new approach to the design of a rough fuzzy controller for the control loop of the SVC (static VAR system) in a two area power system for stability enhancement with particular emphasis on providing effective damping for oscillatory instabilities. The performances of the rough fuzzy and the conventional fuzzy controller are compared with that of the conventional PI controller for a variety of transient disturbances, highlighting the effectiveness of the rough fuzzy controller in damping the inter-area oscillations. The effect of the rough fuzzy controller in improving the CCT (critical clearing time) of the two area system is elaborated in this paper as well.

Foreign Direct Investment, Domestic Investment and Economic Growth in China: A Time Series Analysis

This paper investigates the causal link between foreign direct investment (FDI), domestic investment and economic growth in China for the period 1988–2003 using a multivariate VAR system with error correction model (ECM) and the innovation accounting (variance decomposition and impulse response function analysis) techniques. The results show that while there is a bi‐directional causality between domestic investment and economic growth, there is only a single‐directional causality from FDI to domestic investment and to economic growth. Rather than crowding out domestic investment, FDI is found to be complementary with domestic investment. Thus, FDI has not only assisted in overcoming shortage of capital, it has also stimulated economic growth through complementing domestic investment in China.

The East Asian Miracle: Export-led or Investment-led?

Disagreements persist on whether the Korean and Taiwanese economic miracle is export-led as advocated by market fundamentalists or investment-led as envisioned by the market interventionists. The Granger causality test has been conducted within the context of a VAR system comprised of exports, investment, imports and GDP. The test results show that the fundamentalists' version is more compatible with the data than the interventionists'.

Using Financial Markets Information to Identify Oil Supply Shocks in a Restricted VAR

This paper introduces a methodology for identifying oil supply shocks in a restricted VAR system for a small open economy. Financial market information is used to construct an identification scheme that forces the response of the restricted VAR model to an oil shock to be the same as that implied by futures markets. Impulse responses are then calculated by using a bootstrapping procedure for partial identification. The methodology is applied to Finland and Sweden in illustrative examples in a simple 5-variable model. While oil supply shocks have an inflationary effect on domestic inflation in these countries during the past decade or so, the effect on domestic GDP is more ambiguous.

THREE-DIMENSIONAL VARIATIONAL DATA ASSIMILATION OF MULTIPLE REMOTE SENSING OBSERVATIONS

This study presents a framework to assimilate data observed by a variety of space- and ground-based remote sensing instruments. The framework is based on the WRF 3-D Var system. Data to be assimilated are brightness temperature from TRMM Microwave Imager (TMI), radar reflectivity from conventional radars, precipitable water vapor (PWV) retrieved from GPS observations, and horizontal winds from operational wind profilers. A heavy rainfall case, which was occurred around Kyushu Island in 2003, is chosen for an application. Results indicate that each data can contribute to significant reduction of the inherent spin-up problem. Assimilation of TMI data improves forecasting of convections coming from offshore, which is effective over the lead time of 6-hour. Temperature retrieval with radar reflectivity is necessary for quantitative precipitation forecasting (QPF). GPS-PWV data is useful with TMI data to recover water vapor field. Assimilation of ground-based data has positive impact up to 6-hour ahead at most in this study. After all, QPF with assimilation of all datasets shows the best performance.

Codependence in cointegrated autoregressive models

AbstractThis paper investigates codependent cycles, i.e., transitory components that react to common stimuli in a similar, although not necessarily synchronous fashion. Unlike previous studies, the methodology of this paper allows FIML estimation of the restricted VAR/VECM and therefore the extraction of the unobserved codependent cyclical components via a Beveridge‐Nelson decomposition. It is further shown that the number and order of cofeature combinations that yield the scalar component models associated with codependence is limited by the dimension of a finite‐order VAR system. Monte Carlo simulations indicate that LR tests based on FIML estimates have higher power than alternative GMM and canonical correlations tests, while maintaining good size properties. An empirical application investigates the presence of codependence in UK consumption data. Copyright © 2007 John Wiley & Sons, Ltd.

Sectoral Money Demand Models for the Euro Area Based on a Common Set of Determinants

Empirical money demand analysis undertaken at the aggregate level may obscure behavioural differences between the financial, non-financial corporation and household sectors. Looking at the individual and more homogenous sectors may allow more clearly interpretable empirical relationships between money holding, scale variables and opportunity costs to be estimated. Two possible approaches can be taken to address this issue: aggregate and sectoral money holdings are explained either by a common set of determinant variables or by specific determinants, which may differ across sectors. In this analysis, the first approach has been chosen in order to highlight the different elasticities of the long-run money demand with respect to a common set of macroeconomic determinants and thereby to allow comparison of the model for the aggregate M3 with corresponding models for households, non-financial corporations and non- monetary financial intermediaries. This paper presents results for cointegrated VAR systems estimated over a sample of quarterly data from 1991 to 2005. A SUR system is estimated to cross-check the robustness of the findings and to analyse the importance of common shocks across sectors.

Labor force participation and juvenile delinquency in Taiwan: a time series analysis

This study examines the null hypothesis of Granger no-causality between labor force participation (LFP) and juvenile delinquency in Taiwan. In order to explore this issue more thoroughly, this study adopts the approach proposed by Toda and Yamamoto (1995, Journal of Econometrics, 66(1–2), 225–250). It uses official time-series data provided by the Government of Taiwan. After estimating both a four- and five-variable VAR system, one that substitutes both male and female LFP rates for the aggregate LFP rate, the primary findings of this study reveal the following: The higher the past juvenile crime rate, the lower the future aggregate and female LFP rate will be. In addition, the higher the past male LFP rate, the higher the future juvenile crime rate will be. These findings are quite robust in terms of different lag-length structures.

The Var turbidite system (Ligurian Sea, northwestern Mediterranean)—morphology, sediment supply, construction of turbidite levee and sediment waves: implications for hydrocarbon reservoirs

The Var turbidite system is a small sandy system located in the Ligurian Basin. It was deposited during the Pliocene-Quaternary in a flat-floored basin formed during the Messinian salinity crisis. The system was fed through time by the Var and Paillon canyons that connect directly to the Var and Paillon rivers. It is still active during the present sea-level highstand. Two main mechanisms are responsible for gravity-flow triggering in the Var turbidite system: (1) mass-wasting events affect mainly the upper part of the continental slope, in areas where volumes of fresh sediment delivered by rivers are highest, and result from the under-consolidation state of slope sediments and earthquakes, and (2) high-magnitude river floods resulting from melting of snow and convective rainfall during fall and spring seasons, and generating hyperpycnal turbidity currents at river mouths when the density of freshwater transporting suspended particles exceeds that of ambient seawater. Failure- and flood-induced gravity flows are involved through time in the construction of the Var Sedimentary Ridge, the prominent right-hand levee of the Var system, and sediment waves. Processes of construction of both the Var Ridge and sediment waves are closely connected. Sandy deposits are thick and abundant in the eastern (downchannel) part of the ridge. Their distribution is highly constrained by the strong difference of depositional processes across the sediment waves, potentially resulting through time in the individualization of large and interconnected sand bodies.

Modeling and Application Studies for a Modern Static VAr System Installation

This paper presents a description of modeling and application studies related to a modern static VAr system (SVS) installation in a utility grid. The SVS incorporates a fully integrated static VAr compensator (SVC) and coordinated, automatically switched capacitor banks using a sophisticated control system. The capacitor banks are switched by individual circuit breakers. Descriptions are provided for the SVC control strategy and various levels of modeling details for the application and design studies performed for this device. The stability model described in the paper expands on a previously published work to incorporate the slow susceptance regulator, coordinated/automatic capacitor switching, as well as pertinent protection functions. New insight is presented on the effect of SVC controls on the torsional damping of nearby generators and how such interaction can be easily avoided through proper voltage regulator tuning.

Impact factors

In this paper we discuss sensitivity of forecasts with respect to the information set considered in prediction; a sensitivity measure called impact factor, IF, is defined. This notion is specialized to the case of VAR processes integrated of order 0, 1 and 2. For stationary VARs this measure corresponds to the sum of the impulse response coefficients. For integrated VAR systems, the IF has a direct interpretation in terms of long-run forecasts. Various applications of this concept are reviewed; they include questions of policy effectiveness and of forecast uncertainty due to data revisions. A unified approach to inference on the IF is given, showing under what circumstances standard asymptotic inference can be conducted also in systems integrated of order 1 and 2. It is shown how the results reported here can be used to calculate similar sensitivity measures for models with a simultaneity structure.

A test for multivariate ARCH effects

This paper extends Engle's LM test for ARCH affects to multivariate cases. The size and power properties of this multivariate test for ARCH effects in VAR models are investigated based on asymptotic and bootstrap distributions. Using the asymptotic distribution, deviations of actual size from nominal size do not appear to be very excessive. Nevertheless, there is a tendency for the actual size to overreject the null hypothesis when the nominal size is 1% and underreject the null when the nominal size is 5% or 10%. It is found that using a bootstrap distribution for the multivariate LM test is generally superior in achieving the appropriate size to using the asymptotic distribution when (1) the nominal size is 5%; (2) the sample size is small (40 observations) and/or the VAR system is stable. With a small sample, the power of the test using the bootstrap distribution also appears better at the 5% nominal size.

Output and Inflation Responses to Credit Shocks: Are There Threshold Effects in the Euro Area?

This paper investigates whether output and inflation respond asymmetrically to credit shocks in the euro area. The methodology, based on a non-linear VAR system, follows work by Balke (2000) for the U.S. The results reveal evidence of threshold effects related to credit conditions in the economy. Consistent with this finding, the impulse responses show some signs of asymmetric responses over the lending cycle. However, the results of the paper suggest that in the euro area non-linearities arising from credit market imperfections may be less pronounced than in the U.S., probably reflecting specific institutional features of its banking sector.

Two Sides Of The Same Coin: Bootstrapping The Restricted Vs. Unrestricted Model

The properties of the bootstrap test for restrictions are studied in two versions: 1) bootstrapping under the null hypothesis, restricted, and 2) bootstrapping under the alternative hypothesis, unrestricted. This article demonstrates the equivalence of these two methods, and illustrates the small sample properties of the Wald test for testing Granger-Causality in a stable stationary VAR system by Monte Carlo methods. The analysis regarding the size of the test reveals that, as expected, both bootstrap tests have actual sizes that lie close to the nominal size. Regarding the power of the test, the Wald and bootstrap tests share the same power as the use of the Size-Power Curves on a correct size-adjusted basis.

Voltage Support by Distributed Static VAr Systems (SVS)

This paper shows that when load centers require Static VAR Systems (SVS) for regulated voltage control, the strategy of using many, small, distributed SVS located at distribution buses is more advantageous than a few large bulk SVS located at the transmission or sub-transmission bus. The advantages are (i) standby to meet N-1 reliability criterion is reduced; (ii) costly high voltage transformers are no longer needed because the SVS can be connected directly to the low voltage distribution buses; (iii) distribution-side voltage support is more effective so that the total MVAr requirement of the distributed SVS is less. Simulation studies have demonstrated that the distributed SVS units operate harmoniously together.

Artikel

■ Aim In 2002 the Bergen Clinics Foundation established ‘Føre Var’, a city-wide ‘early warning’ system geared towards the identification, monitoring and reporting of drug and alcohol trends in the city of Bergen, Norway, on a six-monthly basis. The primary goal for the system was the dissemination of earlier, more reliable information on new and emerging trends to enable timely and more effective interventions by policy makers and practitioners in the drug and alcohol field. ■ Methods The Føre Var system triangulates and cross-references a wide range of statistical and quantitative data, including drug seizures data, treatment figures, alcohol sales and a school survey, with information from a number of ‘leading edge' or sensitive data sources, including Internet sites, youth and local media, cultural mapping and key informants. Data is collected from sources every six months, analysed for identifiable patterns and trends, and then disseminated widely. ■ Results & Conclusion This paper details the system's developmental stages and methodologies, in addition to summarizing results from the first three Føre Var reports. Finally, the strengths and weaknesses of the model, its replicability as well as the potential advantages of a city-level network are discussed.

NODAL VOLTAGE CONTROL IN POWER SYSTEMS BASED ON THE MODEL-REFERENCE ADAPTIVE APPROACH

The paper illustrates the design of a power system voltage control scheme based on the model reference adaptive approach. Firstly, for an assigned operating condition, a power system approximated linear model is build-up which represents the system dynamics as seen from the busbar at which the controller is connected. Then, by imposing a desired reference model, the controller parameters are obtained by solving the model-following problem which ensures that the controlled voltage tracks the voltage reference. In presence of unknown operating conditions changes, the regulator parameters are varied according to an adjustment laws designed on the basis of the gradient rule. The task of the adaptation mechanism is to counteract the effects of such changes. Referring to a Static VAR System (SVS) controllable compensator device the adopted model-reference adaptive control scheme has been designed and its performance analyzed by accurate numerical time simulation studies in the case of both unknown load variations and changes in the power system structure, in particular line opening.

Thermoeconomic evaluation and optimization of a double-effect H 2O/LiBr vapour-absorption refrigeration system

In this paper, the thermoeconomic concept is applied to the optimization of a double-effect H 2O/LiBr VAR system, aimed at minimizing its overall product cost. A simplified cost minimization methodology based on the thermoeconomic concept is applied to calculate the economic costs of all the internal flows and products of the system by formulating thermoeconomic cost balances. Once these costs are determined, the system is thermoeconomically evaluated to identify the effects of the design variables on cost of the flows and products. This enables to suggest changes of the design variables that would make the overall system cost-effective. Finally, an approximate optimum design configuration is obtained by means of an iterative procedure. The result shows significant improvement in the system performance. The sensitivity analysis shows that the changes in optimal values of the decision variables are negligible with changes in the fuel cost.

Providing an earlier warning of emerging drug trends: the føre var system

In 2002 the Bergen Clinics Foundation established Føre Var, a citywide ‘earlier warning’ system geared towards the identification, monitoring and reporting of drug and alcohol trends in the city of Bergen, Norway, on a six-monthly basis. The primary goal for the system was the dissemination of earlier, more reliable information on new and emerging trends to enable timely and more effective interventions by policy makers and practitioners in the drug and alcohol field. The Føre Var system triangulates and cross-references a wide range of statistical and quantitative data including seizures data, treatment figures, alcohol sales and a school survey, with information from a number of ‘leading edge’ or sensitive data sources, including Internet sites, youth and local media, cultural mapping and key informants. Data is collected from sources every six months, analysed for identifiable patterns and trends and disseminated widely. This paper details the system's developmental stages and methodologies, in addition to summarizing results from the first three Føre Var reports. In conclusion, the strengths and weaknesses of the model, its replicability as well as the potential advantages of a city-level network are discussed.

Granger causality of the inflation–growth mirror in accession countries*

AbstractThe paper presents a model in which the exogenous money supply causes changes in the inflation rate and the output growth rate. While inflation and growth rate changes occur simultaneously, the inflation acts as a tax on the return to human capital and in this sense induces the growth rate decrease. Shifts in the model's credit sector productivity cause shifts in the income velocity of money that can break the otherwise stable relationship between money, inflation, and output growth. Applied to two accession countries, Hungary and Poland, a VAR system is estimated for each that incorporates endogenously determined multiple structural breaks. Results indicate Granger causality positively from money to inflation and negatively from inflation to growth for both Hungary and Poland, as suggested by the model, although there is some feedback to money for Poland. Three structural breaks are found for each country that are linked to changes in velocity trends, and to the breaks found in the other country.