1002 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 53, NO. 4, AUGUST 2006Power-Electronic Systems for the Grid Integrationof Renewable Energy Sources: A SurveyJuan Manuel Carrasco, Member, IEEE, Leopoldo Garcia Franquelo, Fellow, IEEE,Jan T. Bialasiewicz, Senior Member, IEEE, Eduardo Galván, Member, IEEE,Ramón C. Portillo Guisado, Student Member, IEEE, Ma. Ángeles Martín Prats, Member, IEEE,José Ignacio León, Student Member, IEEE, and Narciso Moreno-Alfonso, Member, IEEEAbstract—The use of distributed energy resources is increas-ingly being pursued as a supplement and an alternative to largeconventional central power stations. The specification of a power-electronic interface is subject to requirements related not only tothe renewable energy source itself but also to its effects on thepower-system operation, especially where the intermittent energysource constitutes a significant part of the total system capacity.In this paper, new trends in power electronics for the integrationof wind and photovoltaic (PV) power generators are presented.A review of the appropriate storage-system technology used forthe integration of intermittent renewable energy sources is alsointroduced. Discussions about common and future trends in re-newable energy systems based on reliability and maturity of eachtechnology are presented.Index Terms—Direct drives, doubly fed induction generator(DFIG), flywheel, hydrogen, multilevel converter topologies, su-percapacitors, superconducting magnetic energy storage (SMES),wind diesel.I. INTRODUCTIONTHE INCREASING number of renewable energy sourcesand distributed generators requires new strategies for theoperation and management of the electricity grid in order tomaintain or even to improve the power-supply reliability andquality. In addition, liberalization of the grids leads to newmanagement structures, in which trading of energy and poweris becoming increasingly important. The power-electronic tech-nology plays an important role in distributed generation and inintegration of renewable energy sources into the electrical grid,and it is widely used and rapidly expanding as these applica-tions become more integrated with the grid-based systems.During the last few years, power electronics has undergonea fast evolution, which is mainly due to two factors. The firstone is the development of fast semiconductor switches thatare capable of switching quickly and handling high powers.The second factor is the introduction of real-time computercontrollers that can implement advanced and complex controlManuscript received March 2, 2006; revised May 17, 2006. Abstract pub-lished on the Internet May 18, 2006.J. M. Carrasco, L. G. Franquelo, E. Galván, R. C. P. Guisado, Ma. Á. M.Prats, J. I. León, and N. Moreno-Alfonso are with the Department of Elec-tronics Engineering, University of Seville, 41092 Seville, Spain (e-mail:[email protected]; [email protected]).J. T. Bialasiewicz is with the Department of Electrical Engineering, Uni-versity of Colorado, and the Health Sciences Center, Denver, CO 80217 USA(e-mail: [email protected]).Digital Object Identifier 10.1109/TIE.2006.878356algorithms. These factors together have led to the developmentof cost-effective and grid-friendly converters.In this paper, new trends in power-electronic technology forthe integration of renewable energy sources and energy-storagesystems are presented. This paper is organized as follows.In Section II, we describe the current technology and futuretrends in variable-speed wind turbines. Wind energy has beendemonstrated to be both technically and economically viable.It is expected that current developments in gearless energytransmission with power-electronic grid interface will lead toa new generation of quiet, efficient, and economical windturbines. In Section III, we present power-conditioning systemsused in grid-connected photovoltaic (PV) generation plants.The continuously decreasing prices for the PV modules leadto the increasing importance of cost reduction of the specificPV converters.Energy storage in an electricity generation and supply systemenables the decoupling of electricity generation from demand.In other words, the electricity that can be produced at timesof either low-demand low-generation cost or from intermittentrenewable energy sources is shifted in time for release attimes of high-demand high-generation cost or when no othergeneration is available. Appropriate integration of renewableenergy sources with storage systems allows for a greater marketpenetration and results in primary energy and emission savings.In Section IV, we present research and development trends inenergy-storage systems used for the grid integration of intermit-tent renewable energy sources.II. WIND-TURBINE TECHNOLOGYA. Variable-Speed Wind TurbinesWind energy has matured to a level of development whereit is ready to become a generally accepted utility generationtechnology. Wind-turbine technology has undergone a dramatictransformation during the last 15 years, developing from afringe science in the 1970s to the wind turbine of the 2000susing the latest in power electronics, aerodynamics, and me-chanical drive train designs [1], [2]. In the last five years,the world wind-turbine market has been growing at over 30%a year, and wind power is playing an increasingly importantrole in electricity generation, especially in countries such asGermany and Spain. The legislation in both countries favorsthe continuing growth of installed capacity. Wind power is quite0278-0046/$20.00 © 2006 IEEECARRASCO et al.: SYSTEMS FOR THE GRID INTEGRATION OF RENEWABLE ENERGY SOURCES 1003Fig. 1. Single doubly fed induction machine with two fully controlled ac–dc power converters.different from the conventional electricity generation with syn-chronous generators. Further, there are differences between thedifferent wind-turbine designs available on the market. Thesedifferences are reflected in the interaction of wind turbineswith the electrical power system. An understanding of this is,therefore, essential for anyone involved in the integration ofwind power into the power system.Moreover, a new technology has been developed in the wind-power market introducing variable-speed working conditionsdepending on the wind speed in order to optimize the energycaptured from the wind. The advantages of variable-speedturbines are that their annual energy capture is about 5%greater than the fixed-speed technology, and
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