Bulletin of Electrical Engineering and Informatics Vol. 13, No. 6, December 2024, pp. 3789~3799 ISSN: 2302-9285, DOI: 10.11591/eei.v13i6.7245  3789 Journal homepage: http://beei.org A frequency adaptive multiple complex coefficient filter for grid connected applications Bachir Boumediene 1 , Rabah Araria 1 , Zakaria Chedjara 1 , Belkacem Mekhloufi 1 , Mohamed Bey 1 , Patrice Wira 2 1 L2GEGI Laboratory, Department of Electrical Engineering, Faculty of Applied Sciences, University of Tiaret, Tiaret, Algeria 2 IUT of Mulhouse, IRIMAS Laboratory, University of Haute Alsace, 61 Rue Albert Camus, Mulhouse, France Article Info ABSTRACT Article history: Received Jul 23, 2023 Revised Apr 8, 2024 Accepted May 16, 2024 In the realm of synchronization techniques, the dichotomy between open loops (OLSs) and closed loops (CLSs) presents a perennial challenge: how to enhance dynamic performance without sacrificing stability and disturbance rejection. While OLS techniques offer rapid dynamic response and unwavering stability, they often falter in non-nominal frequency scenarios. Conversely, CLS techniques grapple with the delicate balance of bolstering dynamic performance while maintaining robust stability. To surmount these obstacles, this study proposes an innovative approach: the integration of a frequency locked loop (FLL) as a secondary frequency detector within synchronization structures, coupled with the multiple-complex coefficient-filter (MCCF). This amalgamation bestows notable advantages. Firstly, from a control perspective, the resultant synchronization technique resembles a quasi-OLS, obviating the need for intricate stability analyses. Moreover, it exhibits commendable disturbances rejection alongside swift dynamic response. Through comprehensive simulation, our proposed technique showcases superiority over existing counterparts, evidencing enhanced settling time, disturbances rejection, and efficiency in the face of frequency drifts. Keywords: Closed loop systems Frequency estimation techniques Frequency locked loop Open-loop systems Phase detection methods Phase locked loop Synchronization algorithms This is an open access article under the CC BY-SA license. Corresponding Author: Bachir Boumediene L2GEGI Laboratory, Department of Electrical Engineering, Faculty of Applied Sciences University of Tiaret Tiaret-14000, Algeria Email: bachir.boumediene@univ-tiaret.dz 1. INTRODUCTION Research in synchronization techniques has recently attracted significant attention thanks to the advances made in small-signal modeling, filtering capability. Point of view control they can be classified into open loops (OLS) and closed loops (CLS) [1]-[31]. The CLS methods are those approaches whose implementation involves feeding back one or more signals, while the OLS are characterized by having no feedback in its structures. The CLS can be categorized into phase locked loops (PLLs), frequency locked loops (FLLs), and other approaches such as least-squares, adaptive observer, and maximum likelihood estimator. The PLLs/FLLs are well recognized in a number of applications such as control of electrical motors, islanding detection, control of converters in more electric aircraft, and vibration suppression in mechanical systems. The pace of developments in the field has accelerated in the last few years, and substantial knowledge has been recently generated. Nevertheless, these two approaches are mathematically equivalent systems. The PLLs are designed to lock the phase angle in synchronous reference frame (SRF), while the FLLs lock the frequency in stationary reference frame. Figure 1 illustrates the block diagram of