Low Voltage Microgrid under Islanded Operation: Control Strategies and Experimental Tests F. Baccino, M. Marinelli, S. Massucco, F. Silvestro Abstract—The paper aims at describing the experimental setup of a low voltage microgrid equipped with distributed energy resources, both renewable and conventional, storage systems and loads. The experimentation involves the validation of control strategies also in islanding operation. The control algorithms are implemented in the Matlab-Simulink environment and run on a laptop connected to the Supervisory Control and Data Acquisition system (SCADA) of the test facility. The objective is to safely and stably operate the system using a Vanadium Redox Battery (VRB) as the only regulating unit in the microgrid, thus using this storage system as the provider of both frequency and voltage control. Different control strategies are tested and their performances evaluated and reported. Keywords - microgrid, islanding operation, storage systems, renewable energy sources, smartgrid I. INTRODUCTION The more and more significant penetration of Distributed Generation (DG) from Renewable Energy Sources (RES) in low voltage distribution networks implies control and operation issues that can be seen as opportunities to enhance new control strategies and network management operation. The resulting microgrids composed by integrated generation, storage and loads could thus be operated in islanded mode with consequent improvements in quality and continuity of service, while at the same time giving a helpful support in avoiding the violation of the grid technical constraints concerning voltage, current and frequency limits. Typically a storage system is coupled with non- programmable RES for different reasons. It can be used to respect an assigned power or energy profile at the point of common coupling [1], to perform actions of peak shaving in those moments in which there is a strong unbalance between generation and load [2] or to maximize the economic profit storing the energy produced when the price is low aiming at selling in those moments in which the price is higher [3]. All these strategies are meaningful while the system is in parallel with the main grid, yet the storage system can be a precious resource in keeping the microgrid running in islanded condition providing the regulation power needed to keep stable the voltage and the frequency without giving up the RES generation. The islanded operation of a small system with significant presence of RES requires controlling units able to cope with fast and wide variations of both production and consumption since it is not possible to trust in the compensations due to the geographical distribution of the resources. The Italian National Standard [4] states that the Distributor can temporarily (e.g. for maintenance) operate portions of the distribution grid in islanded mode previously agreed with the interested active and passive customers. During the islanded operation the quality of service parameters, i.e. frequency and voltage, have to stay within the limits reported in Table I which are less strict than the limits imposed during the normal operation, the values are reported in order to provide a comparison with the experimental results. TABLE IQUALITY OF SERVICE INDEXES LIMITS Index Target Limits Frequency 50 Hz ±5% (2.5 Hz) during 100% of time ±2% (1 Hz) during 100% of time Voltage 400 V +10% (+40 V) -15% (-60 V) The aim of this paper is to describe the experimental setup and the islanded operation of a low voltage microgrid entrusting the task of regulating only to the Vanadium Redox Battery (VRB). In section II the test facility is described along with the different components. In section III the island control strategies are outlined. In section IV the experiment are described focusing on the three different configurations examined and the respective measurements. In section V the results are presented and discussed. II. TEST FACILITY DESCRIPTION The experiments are run in the SYSLAB test facility at DTU Risø Campus. The single line diagram of the test facility is depicted in Figure 1. SYSLAB is a small-scale power system (<100 kW) consisting of real power components interconnected by a 3 phase 400 V AC power grid, and some communication and control nodes interconnected by a dedicated network, all distributed (more than 1 km) over the Risø DTU Campus. The power components include a diesel gen-set, wind power and solar power plants, electricity storage systems, electrical vehicles and controllable loads. The SYSLAB power system can operate in island mode or be connected to the national power system. Focus of SYSLAB is the assessment of the various systems aspects, including system architecture, F. Baccino, M. Marinelli, S. Massucco, F. Silvestro are with the Intelligent Electric Energy Systems Laboratory, University of Genoa, Genoa, Italy (e-mail: francesco.baccino@unige.it; mattia.marinelli@unige.it; stefano.massucco@unige.it; federico.silvestro@unige.it) 8th Mediterranean Conference on Power Generation, Transmission, Distribution and Energy Conversion MEDPOWER 2012