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<!DOCTYPE article PUBLIC "-//NLM//DTD JATS (Z39.96) Journal Publishing DTD v1.0 20120330//EN" "JATS-journalpublishing1.dtd"><article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" article-type="research-article"><front><journal-meta><journal-id journal-id-type="publisher-id">INFORMATICA</journal-id><journal-title-group><journal-title>Informatica</journal-title></journal-title-group><issn pub-type="epub">0868-4952</issn><issn pub-type="ppub">0868-4952</issn><publisher><publisher-name>VU</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="publisher-id">inf22201</article-id><article-id pub-id-type="doi">10.15388/Informatica.2011.320</article-id><article-categories><subj-group subj-group-type="heading"><subject>Research article</subject></subj-group></article-categories><title-group><article-title>Closed-Loop System Identification with Recursive Modifications of the Instrumental Variable Method</article-title></title-group><contrib-group><contrib contrib-type="Author"><name><surname>Atanasov</surname><given-names>Nasko</given-names></name><email xlink:href="mailto:nasko_ratanasov@yahoo.com">nasko_ratanasov@yahoo.com</email><xref ref-type="aff" rid="j_INFORMATICA_aff_000"/></contrib><contrib contrib-type="Author"><name><surname>Ichtev</surname><given-names>Alexandar</given-names></name><email xlink:href="mailto:ichtev@tu-sofia.bg">ichtev@tu-sofia.bg</email><xref ref-type="aff" rid="j_INFORMATICA_aff_001"/></contrib><aff id="j_INFORMATICA_aff_000">Department of Automation, Technical University of Varna, Technical University of Varna, Studentska 1, 9010 Varna, Bulgaria</aff><aff id="j_INFORMATICA_aff_001">Department of Automatics, Technical University of Sofia, Kliment Ohridski 8, 1000 Sofia, Bulgaria</aff></contrib-group><pub-date pub-type="epub"><day>01</day><month>01</month><year>2011</year></pub-date><volume>22</volume><issue>2</issue><fpage>165</fpage><lpage>176</lpage><history><date date-type="received"><day>01</day><month>03</month><year>2009</year></date><date date-type="accepted"><day>01</day><month>03</month><year>2010</year></date></history><abstract><p>The instrumental variable (IV) method is one of the most renowned methods for parameter estimation. Its bigger advantage is that it is applicable for open-loop as well as for closed-loop systems. The main difficulty in closed-loop identification is due to the correlation between the disturbances and the control signal induced by the loop. In order to overcome this problem, additional excitation signal is introduced. Non-recursive modifications of the instrumental variable method for closed-loop system identification on the base of a generalized IV method have been developed (Atanasov and Ichtev, 2009; Gilson and Van den Hof, 2001; Gilson and Van den Hof, 2003). In this paper, recursive algorithms for theses modifications are proposed and investigated. A simulation is carried out in order to illustrate the obtained results.</p></abstract><kwd-group><label>Keywords</label><kwd>closed-loop system identification</kwd><kwd>prediction error</kwd><kwd>instrumental variable method</kwd><kwd>recursive parameter estimation</kwd><kwd>observations</kwd></kwd-group></article-meta></front></article>