Mahmoud Y. Khamaira et al./ Elixir Elec. Engg. 73 (2014) 26432-26435 26432 Introduction Wind power has been one of the most important renewable energy sources over the past decade. The global installed wind power capacity worldwide has significantly increased from 7.272 GW at the end of the year 2002 to 40.56 GW by the end of the year 2011 [1]. In 2008, wind power has produced over 1% of the global electricity generation and by the year 2020; it is estimated to produce about 10% of the global electricity. Currently, doubly fed induction generator (DFIG) is commonly used for wind turbines over 1 MW capacity [1]. DFIG-based wind energy conversion system (WECS) is gaining popularity because of its superior advantages over other wind turbine generator concepts [2, 3] that have seen DFIG application in large WECS reaching 55% of the worldwide total wind capacity during the year 2012 [4]. A typical configuration of DFIG wind turbine is shown in Fig. 1. Rotor side converter (RSC) and grid side converter (GSC) interface the DFIG with the grid. Both converters use forced commutated power electronic switches such as insulated gate bipolar transistors (IGBT) to convert AC to DC and vice versa. A capacitor connected to the DC link of the converter acts as a DC voltage source [5, 6]. The failure of a wind turbine to remain operational for a short time of voltage dip without tripping is referred to the low voltage ride-through (LVRT) capability of the turbine. Rotor crowbar circuit which is relatively a cheap solution with simple control, is usually used to protect the RSC, [4, 7, 8]. There are many papers in the literature that investigated various approaches to compensate WECS reactive power during voltage fluctuation events by mainly connecting a flexible AC transmission system (FACTS) device such as static synchronous compensator (STATCOM) to the point of common coupling (PCC) [9-15]. There is however a few publications considered the compensation of active power as well [16-19]. This paper presents a new topology for the DFIG converters by incorporating a coil within the converters to improve the overall performance of a DFIG-based WECS during faults at the grid side. Simulation is carried out using Simulink/Matlab software. Fig 1. Typical configuration of DFIG System under Study Fig. 2 shows the system under study that consists of six 1.5- MW DFIGs connected to the ac grid at the PCC. Fig 2. Configuration of a DFIG wind turbine equipped with a coil The grid that is represented by an ideal three-phase voltage source of constant frequency is connected to the wind turbines via a 30-km transmission line and step-up transformer. During normal operating conditions, reactive power produced by the wind turbines is regulated at zero MVar to maintain unity power factor connection. For an average wind speed of 15 m/s, which is used in this study, the turbine output active power is 1.0 pu, and the rotor shaft speed is 1.2 pu [3]. A coil is connected to the DC link of the back-to-back power converters of the DFIG through a DC/DC chopper. Tele: E-mail addresses: m.khamaira@student.curtin.edu.au © 2014 Elixir All rights reserved ABSTRACT Doubly Fed Induction Generators (DFIGs) are currently extensively used in variable speed wind power plants due to their superior advantages that include reduced converter rating, low cost, reduced losses, easy implementation of power factor correction schemes, variable speed operation and four quadrants active and reactive power control capabilities. On the other hand, DFIG sensitivity to grid disturbances, especially for voltage sags represents the main disadvantage of the equipment. In this paper, a coil is proposed to be integrated within the DFIG converters to improve the overall performance of a DFIG- based wind energy conversion system (WECS). The charging and discharging of the coil are controlled by controlling the duty cycle of the switches of the dc-dc chopper. Simulation results reveal the effectiveness of the proposed topology in improving the overall performance of the WECS system under study. © 2014 Elixir All rights reserved. A new topology for doubly fed induction generator to improve the overall performance of wind energy conversion system Mahmoud Y. Khamaira, A. Abu-Siada, S. Islam and M. A. S. Masoum Department of Electrical and Computer Engineering, Curtin University Perth, Australia. ARTICLE INFO Article history: Received: 11 June 2014; Received in revised form: 10 August 2014; Accepted: 19 August 2014; Keywords Doubly fed induction generator, Wind energy conversion system, Grid codes. Elixir Elec. Engg. 73 (2014) 26432-26435 Electrical Engineering Available online at www.elixirpublishers.com (Elixir International Journal)