Fast Control Strategy For Stabilizing Fixed Speed Wind Turbines in an Islanded Distributed System

ABSTRACT: Driven by economic, technical and environmental reasons, the energy sector is moving into an era where electrical demand will be met through wide spread installation of distributed resources or what's known as Distributed Generation Systems. This paper deals with a distributed generation system (DGS) with fixed speed induction generator based wind turbines (FSWTs) which are sensitive and vulnerable to voltage disturbances and reactive power deficiency. Consequently, the control and protection strategies should be prompt and precise to avoid undesired wind generator shut down. In this paper, a distributed generation system with three combined heat and power generators (CHPs) and three fixed speed induction generator based wind turbines (FSWTs) is initially connected to the grid and feeding dynamic load groups. A fast control strategy is proposed to stabilize the system when the distributed generation system (DGS) is islanded from grid after the occurrence of a three phase fault. This includes governor and exciter control of CHPs, reactive power compensation, and load shedding. Simulation is done in PSCAD/EMTDC and results are analyzed. KEYWORDS: DGS, FSWTs, CHPs, governor control, reactive-power compensation, load shedding. I.INTRODUCTION The environmental regulations due to green house gas emissions, the electricity business restructuring , and the recent development in small scale power generation are the main factors driving the energy sector in to a new era, where large portions of increase in electrical energy demand are met through widespread installation of distributed resources or what's known as 'Distributed Generation Systems'. DGS facilitate electric power generation in proximity of load centres. As a result, DGS can give commercial consumers various options in a wider range of high reliability-low price combinations.DGS can operate either in a grid-connected mode or in an islanded mode within a micro-grid. In the islanded mode of operation, a cluster of DG units serviced by a distribution system is formed to maintain the reliability of critical loads, mainly when the utility supply is not available. The behaviour of power system is mainly determined by the behaviour and interaction of generators connected to it. When the penetration of wind generation increases its effect on power system also increases. This leads to careful study of stability of power system with wind generators. Not only the renewable generation units, but also the increasing utilization of power electronics devices in a DGS has changed the power system characteristics. Some literatures reveal that the recent large scale system blackouts are increasingly because of voltage collapses caused by reactive power deficiency, rather than frequency drops Conventional system protective schemes, such as under frequency load shedding (UFLS) or under voltage loadshedding (UVLS), may not respond quickly enough after disturbances in the changing power system