In clusters of wind generators spread over small geographic areas, the spatial correlation of wind power production is strong. Simulation of joint power production in such cases-such as for instance for determining the available power in a microgrid-is flawed if the correlation is not properly defined.Several methods have been proposed in the literature for producing scenarios of correlated samples; mostly focused on wind speed. In this paper we analyze three popular choices: classical Monte Carlo (with correlation induced by Cholesky factorization), Latin Hypercube Sampling (with correlation induced by rank sorting), and the recent copula theory. We put together a variety of statistical tools to transform an uncorrelated multivariate sample into a correlated one; and supplement other works by introducing a detailed definition of the wind power distribution and by expanding the Archimedean copula analysis to dimensions beyond the bivariate case analyzed in some related works.We analyze a year of wind production of 210 wind site from NREL data base. We cluster them to give a view of prospective microgrids, and employ several statistical techniques to measure the adequacy of the simulated samples to the original measured data.Our results show that, for generation in small geographic areas, the higher the number of generators, the better the wind power dependence structure is described by LHS. On the contrary, copulas-Gumbel or Gaussian for two-and three-dimensional problems, and Gaussian for higher dimensions-are better suited for representing correlated wind speed. The results are different when the generators are spread over large geographic areas.Compared with LHS endowed with rank sorting for inducing correlation, copula theory is in some sense cumbersome to apply for modeling and simulating wind power data. However, simulations can be performed in prospective microgrids in small geographical areas with larger accuracy by means of LHS if wind power is analyzed rather than wind speed. This advantage is lost for large distances or when small number of generators is considered.
Wind generators provide efficient harvesting of wind energy at the cost of worsening the inertial response during loadfrequency events. The inertial response may be improved, however, by emulating the response of synchronous generators by means of additional control loops that sense frequency deviations. Energy reserve is needed in such a case if overloading, stalling or power request for speed recovery are to be avoided. In this study, the authors formulate an optimal problem to achieve the aim of conciliating the opposite objectives of minimum loss of power production and required minimum inertial reserve. The solution to the problem gives the pitch angles and the associated, modified speed against power tracking characteristics needed to support high kinetic energy storage with minimum loss of power production. The analyses confirm that a proper reserve can be maintained, mainly at low wind speeds, with a reduced amount of de-loading.
Abstract-This paper discusses a multiterminal direct current (MTDC) connection proposed for integration of offshore multi-use platforms into continental grids. Voltage source converters (VSC) were selected for their suitability for multiterminal dc systems and for their flexibility in control. A five terminal VSC-MTDC which includes offshore generation, storage, loads and ac connection, was modeled and simulated in DigSILENT Power Factory software. Voltage margin method has been used for reliable operation of the MTDC system without the need of fast communication. Simulation results show that the proposed system was able to maintain constant dc voltage operation during fluctuations in the generation and changes in the demand. Moreover, it was able to secure power supply to passive loads during loss of a dc voltage regulating terminal and to perform a dispatch scheme where it is possible to buy, sell or store energy attending to the price in the electricity market.
Application of asynchronous machines in wind turbine driven generators is a good alternative due t o their good inherent characteristics such as efficiency, reliability, low cost and power/weight ratio. Nevertheless, when isolated operation is required, the application of external capacitors t o provide self-excitation results in a rather complex analysis which makes the design phase somewhat tedious and of little accuracy. This paper presents one method for the analysis of the operation of self-excited induction generator, which provides also a procedure for the computation of the required external control capacitance and resistance. A number of switchable control capacitors and resistors can be used provide variation in discrete steps in order t o balance active and reactive power. In this paper, the objective is t o develop a dynamic model of the conversion scheme to regulate the frequency and terminal voltage between the limits fixed for performance criteria.
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