Participation in the Frequency Regulation Control of a Resilient Microgrid for a Distribution Network

This paper introduces the results of a research project whose objective is to extend obtained capabilities of a resilient microgrid to a conventional distribution network. This system has been previously sized and optimized to fully operate in an autonomous way. The presented work is an advanced interface control system for grid connection of this cluster in order to provide the over power in compliance with the distribution network. Especially, a frequency regulation function is added into the control system. As a result, the Distribution System Operator considers this locally controlled cluster as a single producer. key words: Resilient microgrid, frequency regulation, control design, interactivity, distribution network. INTRODUCTION The operation of the power grid system requires meeting a few essential reliability objectives like: continuous balancing of generation and demand, transmission system security, emergency preparedness, system control etc. The main change in the future European electricity market will affect the power reserve management [1]. Having a large power reserve will be a key for successful operation. The reserves are usually analyzed as slow access reserves and quick spinning reserve. Currently spinning reserves are the online generating equipments that can increase output immediately in response to variations in frequency or on demand. These reserves can be fully available within 10 minutes. Currently gas turbines and hydraulic power plants are used to provide quick spinning reserves. The increasing need in quick spinning reserves and the politic environmental wishes require finding new clean niches for reserves. This paper presents the results of a research project whose objective is to extend obtained capabilities of a resilient microgrid to a conventional distribution network. An advanced interface control system for grid connection of this cluster is developed in order to provide the available over power in compliance with the distribution network (fig. 1). As a result, the Distribution System Operator (DSO) considers this locally controlled cluster as a potential power reserve contributor. I. CONFIGURATION OF THE CONSIDERED MICROGRID In Europe, a large development of PV and wind generators is awaited and planned to create a sustainable energy system in order to reduce emission of CO2. These renewable energy based generators are well known by grid operators as random energy generators with limited capabilities for providing ancillary services. Figure 1: General organization of the system In order to facilitate the integration of more renewable energy based generators, a possible solution is to associate them with local conventional generators, local storage units and a set of local flexible loads. The optimum management of this energy system is the key to increase the efficiency, the supply, the safety, reliability and quality of the energy distribution in this local area for end-users [2]. This future active network has to coordinate small and medium scale power sources with consumer demands, allowing both to decide the best operation in real time. It can be viewed as a microgrid, which is able to locally control a cluster of generators and flexible loads in a decentralized way and to permit renewable energy based generators to provide their full benefits. Practical implementations are under development in Europe at Kytnos island (Greece), at Mannheim-Wallstadt (Germany) [3]. The studied microgrid comprises a 30kW Gas Micro Turbine (GMT), 17kW PV generators and a total of 30kW end-users (fig. 2). This system has been previously sized and optimized to fully operate in an autonomous way. All sources are grid-connected with power electronic converters within a dedicated control system International Journal of Integrated Energy Systems, Vol.1, No1, January-June 2009 Page 2 / 5 and communication interface with a Microgrid Energy Management System (MEMS). Inside this microgrid two units of 2.3kW.min of ultra capacitors are used as energy buffer in order to smooth PV powers and to track the optimal operating point of the GMT unless load variations and PV power production variations. Figure 2: Synoptic of the studied microgrid with useful powers II. INTERACTIVE INTERFACE WITH THE DISTRIBUTION NETWORK General description The interactive interface implements the grid integration of the microgrid and coordination with the distribution network (fig. 1). It includes frequency and voltage control algorithms at the PCC within a gridpower flow assessment, protections and additional measurements. In this paper we just detail the droop controller for the primary frequency control and power exchange with the distribution network. First we recall the fundamental principle of the primary and secondary frequency control of the grid and then we will detail the necessary functions inside the interactive interface to adapt the operating the microgrid with the distribution network. Microgrid Energy Management System ... PSC_ref PMT_ref pv P )