C I R E D CIRED Seminar 2008: SmartGrids for Distribution Frankfurt, 23 - 24 June 2008 Paper 132 CIRED Seminar 2008: SmartGrids for Distribution Paper No 132 Page 1 / 5 OPERATION AND CONTROL OF DG BASED POWER ISLAND IN SMART GRID ENVIRONMENT S.P.CHOWDHURY S.CHOWDHURY C.F.TEN P.A.CROSSLEY Jadavpur University–India Women’s Polytechnic–India University of Manchester–UK University of Manchester - UK spchowdhury63@yahoo.com sunetra69@yahoo.com chui.ten@postgrad.manchester.ac.uk p.crossley@manchester.ac.uk ABSTRACT This paper presents a simulation study of operation and control of distributed generators (DGs) in power islands in Smart Grid environment. It examines the technical feasibility of DG islanding operation to exploit their services for improving electrical safety, security and quality of energy supply. The grid-connected DGs are initially operated at PQ mode and then switched to V-f mode to have full controllability of bus frequency and voltage when operated as independent power island. Suitable controllers are designed separately for individual control of voltage and frequency at the DG bus. The simulation results are validated through several case studies using DIgSILENT software for both intentional and unintentional loss of grid (LOG) situations. It has been observed that when several islanded DGs are interconnected to form a power island, they can share the active and reactive power demands of the island leading to quick restoration of the system voltage and frequency within permissible bandwidth. INTRODUCTION With growing power demand and increasing concern about the use of fossil fuels in conventional power plants, the new paradigm of distributed generation is gaining greater commercial and technical importance across the globe. Distributed generation involves the interconnection of small-scale, on-site distributed generators (DGs) with the main power utility at distribution voltage level [1]. DGs constitute non-conventional and renewable energy sources like solar photovoltaic, wind turbines, fuel cells, mini- hydro, micro-turbines etc. These generation technologies are being preferred for their high energy efficiency, low environmental impact and their applicability as uninterruptible power supplies. Electric energy market reforms and developments in electronics and communication technology are currently enabling the control of geographically distributed DGs through advanced SCADA [2]. R.H.Lasseter et. al. [3] have discussed how interconnected DGs can be efficiently operated as microgrids both in grid-connected mode and islanded mode. A high degree of DG penetration (more than 20%) as well as their placement and capacity with respect to the utility grid, have considerable impact on operation, control, protection and reliability of the existing power system [3][4][5]. These issues must be critically assessed and resolved before allowing the market participation of DGs. This is necessary for fully utilising DG potential for generation augmentation, enhancing power quality and reliability and for providing auxiliary services such as active reserve, load-following, interruptible loads, reactive reserve, restoration etc. [6]. Literature survey indicates that extensive work has been done to elucidate the impacts of DG penetration on utility system and to provide possible solutions. Most critically affected area is protection coordination of the utility distribution system. Singly-fed and passive utility distribution networks are converted to multi-fed networks after DG insertion. This changes the flow of fault currents from unidirectional to bi-directional which affects the coordination of the existing protective devices. Other impacts include i) false tripping of feeders and protective devices, ii) blinding of protection, iii) change of fault levels with connection and disconnection of DGs, iv) unwanted islanding, v) prevention of automatic reclosing and vi) out of synchronism reclosing [7][8]. Keeping these in view, technical recommendations like G83/1, G59/1, IEEE 1547, CEI 11-20 prescribe that DGs should be automatically disconnected from the MV and LV utility networks, in case of tripping of the circuit breaker (CB) supplying the feeder connected to the DG. This is known as the anti-islanding feature and is incorporated as a mandatory feature in the inverter interfaces for commercially available DGs. Anti-islanding systems are mainly used to ensure personnel safety at the grid end and to prevent any out of synchronism reclosure. As the DGs are not under direct utility control, use of anti-islanding protection is justified by the operational requirements of the utilities [9]. Extensive research is being carried out to develop low-cost and efficient digital anti-islanding schemes suitable for seamless operation of the inter-tie CBs for re-connection of the islanded zones without affecting original protection co-ordination of the utility grid [9-11][13-16]. Anti-islanding feature drastically reduces the benefits of DG deployment which could otherwise be exploited if DGs were allowed to operate as power islands as and when required. Intentional power island operation allows the DGs to operate as independent islanded network suitable for maintaining uninterruptible power supply to critical loads. At present, in spite of increasing DG penetration, power engineers, network operators, regulators and other stake- holders are hesitant to such initiatives. Different surveys indicate that the present scenario does not economically justify this mode of DG operation. However, technical studies [12][17] clearly indicate the need to review parts of Authorized licensed use limited to: The University of Manchester. Downloaded on October 9, 2008 at 07:15 from IEEE Xplore. Restrictions apply.