Parallel Operation of Uninterruptible Power Supply Systems in MicroGrids Josep M. Guerrero 1 , Juan C. Vásquez 1 , José Matas 1,2 , Jorge L. Sosa 3,4 , Luis García de Vicuña 2 UNIVERSITAT POLITÈCNICA DE CATALUNYA (UPC) 1 Dept. of Automatic Control Systems and Computer Eng., UPC, Spain Distributed Generation and Renewable Energy Research Group, CEIB 2 Dept. of Electronic Eng., UPC, Spain 3 Dept. of Electrical Eng., UPC, Spain 4 Universidad de los Andes. Mérida, Venezuela Escola Universitària d’Enginyeria Tècnica Industrial de Barcelona (EUETIB) Renewable Energy Lab C. Comte d’Urgell, 187. 08036 Barcelona, Spain Telephone: +34 93 413 74 58 / Fax: +34 93 413 74 01 josep.m.guerrero@upc.edu Acknowledgments This work was suported by the Spanish Ministry of Science and Technology under grant CICYT ENE 2006-15521-C03-01/CON, and by the Consorci de l’Escola Industrial de Barcelona. Keywords Converter control, distribution of electrical energy, uninterruptible power supplies (UPS). Abstract In this paper, a control scheme applied to distributed UPSs forming a microgrid is proposed. The control architecture consists of two levels of hierarchy: 1) the P/Q droop control method of every UPS unit and 2) the management of the microgrid through the control of the setpoints of the units, and the connection or disconnection to the utility mains. 1. Introduction Renewable energy systems are growing up due to not only environmental aspects but also due to social, economical, and political interests. The variable nature of these systems such as photovoltaic or wind energy relies on natural phenomenon like the sun or the wind. Consequently, it is difficult to predict the power that we can obtain through these prime sources, and the peaks of power demand do not coincide necessarily with the generation peaks. Hence, storage energy systems are required if we want to supply the local loads in an uninterruptible power supply (UPS) fashion [1], [2]. Some small and distributed energy storage systems can be used for this purpose, such as: flow batteries, fuel cells, flywheels, superconductor inductors, or compressed air devices. The distributed generation (DG) concept is taking importance, pointing out that the future utility line will be formed by distributed energy resources and small grids (minigrids or microgrids) interconnected between them. In fact, the responsibility of the final user is to produce and storage part of the electrical power of the whole system. This change of paradigm let the microgrid export and import energy to the utility through the point of common coupling (PCC). And, when there is a utility failure, the microgrid still can work as an autonomous grid [3]. As a consequence, these two classical applications: grid-connected and islanded operations can be used in the same application. In this sense, the droop control method is proposed as a good solution to connect in parallel several inverters in island mode [4]. However, although it has been investigated and improved, this method by itself is not suitable for the coming flexible microgrids. Authorized licensed use limited to: UNIVERSITAT POLITECNICA DE CATALUNYA. Downloaded on May 09,2022 at 11:36:39 UTC from IEEE Xplore. Restrictions apply.