Technological University Dublin ARROW@TU Dublin Articles School of Electrical and Electronic Engineering 2013 A Review of Existing Microgrid Architectures Lubna Mariam Technological University Dublin Malabika Basu Technological University Dublin, [email protected] Michael Conlon Technological University Dublin, [email protected] Follow this and additional works at: https://arrow.tudublin.ie/engscheleart2 Part of the Electrical and Computer Engineering Commons Recommended Citation Mariam, L., Basu, M. & Conlon, M. (2013). A review of existing microgrid architectures. Journal of Engineering, vol. 2013, pp.1-8. http://dx.doi.org/10.1155/2013/937614 This Article is brought to you for free and open access by the School of Electrical and Electronic Engineering at ARROW@TU Dublin. It has been accepted for inclusion in Articles by an authorized administrator of ARROW@TU Dublin. For more information, please contact [email protected], [email protected]. This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License Hindawi Publishing Corporation Journal of Engineering Volume 2013, Article ID 937614, 8 pages http://dx.doi.org/10.1155/2013/937614 Review Article A Review of Existing Microgrid Architectures Lubna Mariam, Malabika Basu, and Michael F. Conlon Electrical Power Research Centre (EPRC), School of Electrical and Electronic Engineering, Dublin Institute of Technology, Kevin Street, Dublin 8, Ireland Correspondence should be addressed to Malabika Basu; [email protected] Received 13 December 2012; Revised 28 February 2013; Accepted 2 March 2013 Academic Editor: Keat Teong Lee Copyright © 2013 Lubna Mariam et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The future electricity network must be flexible, accessible, reliable, and economic according to the worldwide smartgrid initiative. This is also echoed by the Sustainable Energy Authority of Ireland (SEAI) and European Electricity Grid Initiative (EEGI). In order to facilitate these objectives and to reduce green house gas (GHG) emission, research on various configurations of microgrid (G) system is gaining importance, particularly with high penetration of renewable energy sources. Depending on the resource availability, geographical locations, load demand, and existing electrical transmission and distribution system, G can be either connected to the grid or can work in an autonomous mode. Storage can also be a part of the G architecture. This paper presents a critical literature review of various G architectures. The benefits of grid-connected or isolated G with storage have also been identified. 1. Introduction One of the major aims of G is to combine benefits of nonconventional/renewable low-carbon generation tech- The term microgrid (G) refers to the concept of single elec- nologies and high efficient combined heat and power (CHP) trical power subsystems associated with a small number of systems. The choice of a distributed generator mainly distributed energy resources (DERs), both renewable and/or depends on the climate and topology of the region. Sustaina- conventional sources, including photovoltaic, wind power, bility of a G system depends on the energy scenario, strategy, hydro, internal combustion engine, gas turbine, and micro- and policy of that country and it varies from region to region. turbine together with a cluster of loads [1, 2]. The application Thesetopicsarebeyondthescopeofthisreview. of individual distributed energy resources as microgeneration This paper critically reviews the existing and simulated can cause problems such as local voltage rise, the potential G systems demonstrated in European regions by classifying to exceed thermal limits of certain lines and transformers, their architecture based on integration with the grid, dis- islanding and have high capital cost [3]. Microgrid can be a tribution system, communication system, energy resource, better solution for these problems. In a Gsystem,theDERs and storage. A short description of the advantages and dis- must be equipped with proper power electronic interfaces advantages of the widely available and feasible distributed (PEIs) and control to ensure the flexibility to operate as a generators (DGs) is provided. The benefits of storage and the single aggregated system maintaining the power quality and existing storage devices have been identified. The advantages energy output [4]. From the grid point of view, the main and disadvantages of different distribution systems are also advantage of a Gisthatitistreatedasacontrolledentity presented. within the power system which can operate as a single load. From customers’ point of view, Gs are beneficial because 2. Basic G Architecture they can meet their electrical and heat requirement locally, supply uninterruptible power, improve power quality (PQ), The basic architecture of a GsystemispresentedinFigure 1, reduce feeder loss, and provide voltage support. Furthermore which shows that a G system generally consists of dis- Gs can reduce environmental pollution and global warming tributed generation (DG) resource, storage systems, distribu- by utilizing low-carbon technology [4]. tion systems, and communication and control systems. 2 Journal of Engineering Grid PCC Storage DG − + MGCC ∼ ∼ ∼ MC LC MC DG Load Storage Load LC ∼ ∼ ∼ MC LC MC MC Load LC Load DG Microgrid architecture Communication and control MC Microgeneration control Electrical Network MGCC Microgrid system central control LC Local control Figure 1: A simple microgrid architecture. 2.1. Distributed Generation (DG) Sources. Distributed gen- heatandpower(CHP)actsasatotalsystemwhenheating eration technologies applicable for Gmayincludeemerg- is also used with electricity. Different kinds of sources are ing technologies such as—wind turbine, solar PV, micro- being used in CHP systems such as microturbines (generally hydropower, diesel, and some well-established technologies driven by natural gas, hydrogen, and biogas), Stirling engines, like single-phase and three-phase induction generators, syn- and IC engines. CHP system allows optimum usage of energy chronous generators driven by IC engines [9]. Combined by capturing the excess heat, thereby achieving efficiency Journal of Engineering 3 Table 1: Typical characteristics of common DG sources [5, 6]. Characteristics Solar Wind Microhydro Diesel CHP Geographical location Geographical location Geographical Availability Any time Dependent on source dependent dependent location dependent Output power DC AC AC AC AC GHG emission None None None High Dependent on source Control Uncontrollable Uncontrollable Uncontrollable Controllable Dependent on source Typical Power electronic converter Power electronic converter Synchronous or Synchronous None interface (DC-DC-AC) (AC-DC-AC) induction generator generator Power flow MPPT & DC link voltage MPPT, pitch & torque Controllable Controllable AVR and governor control controls (+P, ±Q) control (+P, ±Q) (+P, ±Q) (+P, ±Q) (+P, ±Q) values of more than 80%, compared to that of about 35% for the energy to the induction generator through the gearbox. conventional power plants [14]. Table 1 shows some typical The generator shaft is driven by the wind turbine to generate characteristics of commonly used DG sources. electric power. Wind turbines may have horizontal axis or vertical axis configuration. The average commercial turbine 2.1.1. Photovoltaic (PV) System. Solar PV generation involves size was 300 kW until the mid 1990s, but recently machines the generation of electricity from solar energy. Due to enor- of larger capacity, up to 5 MW and more, have been developed mous improvement in inverter technologies, PV generation and installed [16]. is now preferred worldwide as Distributed Energy Resources (DERs). The major advantages of a PV system are 2.1.3. Micro-Hydropower System. Micro-hydropower system uses the energy of flowing water to produce mechanical or (i) the sustainable nature of solar energy, electrical energy. This energy generation system depends on (ii) positive environmental impact, the topography and annual precipitation of the area. The sys- tem suffers from large variation of water flow due to uneven (iii) longer life time and silent operation. rainfall and results in a variation in generation [17]. Run- Although photovoltaic (PV) cells can be effectively used of-river system is often used in micro-hydropower systems as DERs in G systems, they have some disadvantages includ- which do not require large storage reservoir. A portion of ing the river water is diverted to a water-conveyance channel torotateaturbineorawaterwheelthatspinsashaft.The (i) high installation cost, motion of the shaft can be used for mechanical power such (ii) low energy efficiency, as pumping water or can be used to power a generator to generate electricity. (iii) restriction to certain locations and weather depen- dence. 2.2. Storage Systems. One of the main criteria of successful It has been reported that small PV installations are more operation of G is the inclusion of energy storage devices, cost effective than the larger ones4 [ ]. As the nature of PV which balances the short-term power and energy demand generation is DC power, a suitable type of power converter with generation. Generally the G power systems have stor- must be employed to convert the DC voltage to AC voltage. age through the generator