Stability analysis and reactive power compensation issue in a microgrid with a DFIG based WECS Asit Mohanty a,⇑ , Meera Viswavandya b , Prakash K. Ray c , Sandipan Patra c a Department of Electrical Engineering, Motilal Nehru National Institute of Technology, Allahabad 211004, India b Department of Electrical Engineering, CET, Bhubaneswar, India c Department of Electrical Engineering, IIIT, Bhubaneswar, India article info Article history: Received 2 July 2013 Received in revised form 26 April 2014 Accepted 13 May 2014 Keywords: ANFIS DFIG Reactive power compensation Synchronous generator UPFC Wind–diesel hybrid system abstract This paper presents a novel methodology for compensating reactive power in a microgrid, having a DFIG based wind–diesel system, to enhance the voltage stability of the hybrid system. UPFC as a FACTS device is proposed in order to improve the control of reactive power mismatch and the stability of the system. A small signal model of the wind–diesel system, DFIG based wind turbine system, UPFC and the controllers are designed for the stability analysis. Further, the voltage variation and reactive power compensation is analysed with the incorporation of proposed ANFIS based UPFC controller. Simulations are performed in MATLAB environment for transient stability analysis in a wind–diesel based microgrid with different wind power input and 2% step increase in load demand. Simulation results illustrate the efficiency and effectiveness of the proposed approach and its impact upon transient behaviour of the microgrid. Ó 2014 Elsevier Ltd. All rights reserved. Introduction Increase in energy demand and depletion of fossil fuel have led to the upsurge of Renewable Energy Sources (RES) and Distributed Generations (DGs) like wind, photovoltaic (PV), fuel cell (FC), and diesel engine generator (DEG). The popularity of RES are due to their non-exhaustible and environment friendly characteristics. Now-a-days researchers are putting emphasis upon decentralised power supply and therefore centralised power supply is being supported by Distributed Generation Sources. As the size and rat- ing of the DG is always small in comparison with the conventional resources, they are connected in the distribution system near to the consumers. This helps in reducing energy loss that occurs during transmission. DG can also efficiently improve the voltage profile of the system by providing the reactive power support [1]. The different types of RES and DG can be integrated to form microgrid which can increase the reliability of power supply into the load. The main advantage of microgrid is that it operates inde- pendently in an isolated manner whenever there is a fault in the inter connected power network, i.e., distributed energy resources can operate either independently or in grid-connected mode as per the system requirement. In the inter-connected power system, as the centralized control becomes more complex, controllers are provided in a decentralized manner in order to improve the system performance. Some of the vital issues like voltage instability and reactive power imbalance are better addressed in an isolated mode and decentralized system. Under these circumstances, wind–diesel hybrid systems are widely used because of their reliability. It is a system in which a wind turbine combines with a diesel generator to provide uninter- ruptible power in standalone mode. Normally, a synchronous generator is preferred to act as diesel generator and induction gen- erator is used in wind turbine for improved performance [2–6]. Induction generators are preferred because of its rugged character- istics. But, it consumes reactive power while in operation which may affect the system voltage. Generally, variable speed wind tur- bines are equipped with doubly fed induction generators (DFIGs) [7–11] and due to its wide operating range, they are preferably used. According to the [12,13] active and reactive power of DFIG is regulated by the rotor current which is controlled through the output voltage of the rotor side converter. So, the applied voltage of the rotor is the direct control variable. DFIG is widely accepted because of its ability to supply power at constant voltage and fre- quency with the variation of rotor speed. DFIG based Wind Energy Conversion System (WECS) employs back to back converters in the rotor circuit where rotor side ensures decoupling control of stator side active and reactive power. http://dx.doi.org/10.1016/j.ijepes.2014.05.033 0142-0615/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +91 9437920530. E-mail address: asithimansu@gmail.com (A. Mohanty). Electrical Power and Energy Systems 62 (2014) 753–762 Contents lists available at ScienceDirect Electrical Power and Energy Systems journal homepage: www.elsevier.com/locate/ijepes