1598IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 24, NO. 3, JULY 2009Distributed Generation Interfaceto the CERTS MicrogridHassan Nikkhajoei, Member, IEEE, and Robert H. Lasseter, Fellow, IEEEAbstract—This paper focuses on the energy storage system andthe power electronic interface included in microsources of theCERTS microgrid. CERTS stands for the Consortium for ElectricReliability Technology Solutions. The consortium was formed in1999 to research, develop, and disseminate new methods, tools,and technologies to protect and enhance the reliability of the U.S.electric power system and efficiency of competitive electricitymarkets. To provide the plug-and-play feature and the powerquality requirements of the CERTS microgrid, all microsourcesregardless of their prime mover type must have a unified dy-namic performance. This necessitates attaching an energy storagemodule to some or all of the microsources. The storage module isattached to the prime mover through a power electronic interfacethat couples the microsource to the microgrid. Details of theenergy storage module, the power electronic interface and thecorresponding controls are described. Performance ofan examplemicrosource, which includes a synchronous generator, a storagemodule and an electronic interface, is studied. Dynamic perfor-mance of the example microsource when operating in the CERTSmicrogrid is evaluated based on digital time-domain simulations inthe EMTP-RV software environment. Effectiveness of the storagemodule, the electronic interface and the corresponding controls inenhancing the microsource performance is verified.Index Terms—Distributed generation (DG), dynamics, elec-tronic interface, energy storage, microgrid, microsource, powerquality.I. INTRODUCTIONDtechnical, economical and environmental issues ofconventionalpower systems [1]–[3]. Distribution of generation units withinan electric power system offers technical advantages in termsof power quality and reliability as well as energy managementand efficiency. It also offers economical advantages in termsof reducing capital investment for construction of power sys-tems since distribution of generation units eliminates the needfor having extensive transmission systems. DG power systemsprovide environmental benefits as a result ofoffering a more ef-ficient way of generating and distributing electricity as well asenabling the integration of renewable energy resources [4]. AsISTRIBUTED generation (DG) is a promising conceptthat is considered as an alternative solution foraddressingManuscript received July 20, 2007; revised August 06, 2008. Current versionpublished June 24, 2009. Paper no. TPWRD-00462-2007.H. Nikkhajoei is with the Department of Electrical Engineering, UnitedArab Emirates University, Al-Ain, United Arab Emirates (e-mail: nikkha-joei@uaeu.ac.ae).R. H. Lasseter is with the Department of Electrical and Computer Engi-neering, University of Wisconsin-Madison, Madison, WI 53706-1691 USA(e-mail: lasseter@engr.wisc.edu).Color versions ofone or more ofthe figures in this paper are available onlineat http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/TPWRD.2009.2021040a new concept for the electric power industry, the applicationofDG for power systems is under extensive studies and experi-mental tests and there are many technical issues in terms of theoperation, control and protection of DG systems [5]–[7].An alternative solution to realize the emerging potential ofDG is to view the Distributed Resources (DR) and the asso-ciated loads as a small power system that is called microgrid.The Consortium for Electric Reliability Technology Solutions(CERTS) microgridemploys anadvancedapproachthat enablesintegrating anunlimitednumberofDRs withthe electricitygrid,withoutrequiring changes inthe structure ofexisting powersys-tems [8]. The CERTS microgrid concept is driven by the fol-lowing principles: 1) a system perspective for customers, utili-ties and society to capture the full benefits of integrating DRswith the electricity grid and 2) a business motivation for ac-celerating adoption of the microgrid concept by reducing thecorresponding initial investment and enhancing the value ofmi-crogrids [9]. The goal of developing the CERTS microgrid isto accelerate realization of small scale DG systems that offerattractive advantages, such as 1) supplying waste heat to build-ings, that eliminates the need for extensive thermal distributionnetworks and 2) enhancing the quality ofpower which is deliv-ered to sensitive loads [6].The CERTS microgrid requires that all of its microsourceshave a unified dynamic performance, regardless of their primemover type. This ensures the plug-and-play feature and thepower quality performance that are expected from the CERTSmicrogrid. Prime movers such as internal combustion engines,gas turbines, microturbines, photovoltaics, fuel cells and windturbines have different dynamics depending on the prime moversize and the technology used. To provide a unified dynamicperformance for microsources with different prime movers, anenergy storage module must be included in the microsources.A power electronic interface controls the operation of storagemodule based on dynamics of the prime mover. This ensuresthat all microsources have the same load-following perfor-mance at their point of coupling with the microgrid. Thispaper describes the operation of CERTS microgrid, detailsof an energy storage module and an electronic interface formicrosources, and detailed simulation of a variable-speedsynchronous generator-based microsource when operating inthe CERTS microgrid.II. CERTS MICROGRIDThe CERTS microgrid has two critical components, the staticswitch and the microsource. The static switch has the ability toautonomously island the microgrid from disturbances such asfaults, IEEE 1547 events and power quality events. The CERTS0885-8977/$25.00 © 2009 IEEE
