Variable speed DFIG wind energy system for power generation and harmonic current mitigation A. Gaillard a , P. Poure b, * , S. Saadate a , M. Machmoum c a Groupe de Recherche en Electrotechnique et Electronique de Nancy, Nancy Universite´ – Universite´ Henri Poincare ´ Nancy 1, BP239, 54506 Vandoeuvre le`s Nancy Cedex, France b Laboratoire d’Instrumentation Electronique de Nancy, Nancy Universite´ – Universite´ Henri Poincare´ Nancy 1, BP239, 54506 Vandoeuvre le`s Nancy Cedex, France c IREENA, 37 Boulevard de l’Universite´, BP 406, 44602 Saint-Nazaire Cedex, France article info Article history: Received 5 April 2008 Accepted 5 November 2008 Available online 18 January 2009 Keywords: Active filter Harmonics Doubly fed induction generator Wind energy conversion system Wind power generation Power quality abstract This paper presents a novel approach for simultaneous power generation and harmonic current miti- gation using variable speed WECS with DFIG. A new control strategy is proposed to upgrade the DFIG control to achieve simultaneously a green active and reactive power source with active filtering capa- bility. To ensure high filtering performance, we studied an improved harmonic isolator in the time- domain, based on a new high selectivity filter developed in our laboratory. We examined two solutions for harmonic current mitigation: first, by compensating the whole harmonic component of the grid currents or second, by selective isolation of the predominant harmonic currents to ensure active filtering of the 5th and 7th harmonics. Simulation results for a 3 MW WECS with DFIG confirm the effectiveness and the performance of the two proposed approaches. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Wind energy is becoming one of the most important renewable energy sources. Recently, power converter control has mostly been studied and developed for WECS integration in the electrical grid. The use of power electronic converters allows variable speed operation of the wind turbine where the WECS extracts maximum power from the turbine. Although WECS uses an electric generator that could be coupled directly to the electrical grid, the power electronics interface is commonly used nowadays. One can take advantage of the power electronic interface to provide some of the ancillary services such as harmonic current mitigation, simultaneously with power genera- tion [1]. These services are provided in addition to active power generation, reactive absorption and injection to achieve voltage control, regulation and correction to meet load variations [2–4]. Electric utility grid systems cannot accept further connection of new generation plants without strict conditions of power quality. In fact, IEEE Standard 1547-2003 (Standard for Interconnecting Distributed Resources with Electric Power Systems) is under final construction [5]. Power quality becomes a major aspect in inte- grating WECS to grids. Furthermore, grids are now dealing with a continuous increase of directly connected non-linear loads such as power electronics converters and large AC drives. As far as the authors know, only a few groups of researchers have addressed the issue of making use of the built-in WECS converters to improve grid power quality and achieve harmonic current mitigation. However, active power filtering function can also be achieved thanks to the WECS power electronics interface. Barbosa et al. proposed a control strategy for grid connected DC–AC converters with load power factor correction [6]. Macken et al. studied the compensation of distorted currents through multiple converter-interfaced renew- able generation units [7]. Recently, Abolhassani et al. presented a sensorless field oriented control of an integrated electric alter- nator capable of controlling the amount of harmonic compensation [8]. More recently, Jain and Ranganathan studied a wound rotor induction generator with sensorless control and integrated active filter for feeding non-linear loads in a stand-alone grid [9]. In the DFIG case, one can also think of using a suited rotor side control to cancel the most significant and troublesome harmonic currents of the utility grid. Abbreviations: AC, alternating current; DC, direct current; DFIG, doubly fed induction generator; FFT, fast Fourier transform; GSC, grid side converter; HSF, high selectivity filter; IGBT, insulated gate bipolar transistor; MPPT, maximum power point tracking; PCC, point common of coupling; PLL, phase locked loop; PWM, pulse width modulation; RSC, rotor side converter; THD, total harmonic distortion; WECS, wind energy conversion system. * Corresponding author. Laboratoire d’Instrumentation Electronique de Nancy, LIEN, EA 3440, Nancy-University, Faculte´ des Sciences et Techniques, BP 239, 54506 Vandoeuvre le`s Nancy Cedex, France. Tel.: þ33 383 684 160; fax: þ33 383 684 153. E-mail addresses: arnaud.gaillard@green.uhp-nancy.fr (A. Gaillard), philip- pe.poure@lien.uhp-nancy.fr (P. Poure), shahrokh.saadate@green.uhp-nancy.fr (S. Saadate), mohamed.machmoum@univ-nantes.fr (M. Machmoum). Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene 0960-1481/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2008.11.002 Renewable Energy 34 (2009) 1545–1553