Inter national J our nal of P o wer Electr onics and Dri v e System (IJPEDS) V ol. 17, No. 2, June 2026, pp. 933 ∼ 945 ISSN: 2088-8694, DOI: 10.11591/ijpeds.v17.i2.pp933-945 ❒ 933 Impr o v ed contr ol strategy f or harmonic curr ent mitigation in DFIG-based wind turbines supplying linear and nonlinear loads Hind Elaimani, Nour eddine Elmouhi Laboratory of Inno v ation in Management and Engineering, Edv antis Higher Education Group, ISGA, Rabat, Morocco Article Inf o Article history: Recei v ed Sep 8, 2025 Re vised Mar 8, 2026 Accepted Apr 23, 2026 K eyw ords: Acti v e lter DFIG Harmonic mitig ation Sliding mode THD ABSTRA CT Impro ving po wer quality is a major challenge in grid-connected wind ener gy systems, especially under mix ed linear and nonlinear load conditions. This paper proposes an enhanced control strate gy for harmonic current mitig ation in a doubly fed induction generator (DFIG)-based wind turbine. The proposed approach inte grates ux-oriented v ector control with an acti v e harmonic compensation algorithm implemented through the rotor -side con v erter (RSC). Unlik e con v entional methods that tar get only specic harmonic orders, the proposed strate gy mitig ates all current harmonics at the point of common coupling (PCC). Simulation studies conducted under v arious load conditions demonstrate that the method signicantly reduces the total harmonic distortion (THD) and ensures near -sinusoidal stator currents. The results conrm the ef fecti v eness and rob ustness of the proposed control approach in impro ving the po wer quality of DFIG-based wind ener gy con v ersion systems. This is an open access article under the CC BY -SA license . Corresponding A uthor: Hind Elaimani Laboratory of Inno v ation in Management and Engineering, Edv antis Higher Education Group, ISGA 27, A v enue Oqba, 27 A v . Oqba Ibn Naa, Rabat 10090, Morocco Email: h.elaimani@gmail.com 1. INTR ODUCTION In recent decades, the global demand for electri cal ener gy has increased rapidly due to industrializat ion and the widespread use of electrical appliances [1], [2]. T o meet this gro wing demand while reducing en vironmental impact, man y countries are inte grating rene w able ener gy sources into their po wer systems, with wind ener gy emer ging as a prominent option due to its high potential and reliabilit y . Se v eral recent studies ha v e in v estig ated harmonic mitig ation in rene w able ener gy systems. A rst w ork [3] implemented a unied po wer quality conditioner (UPQC) combining series and shunt acti v e lters to reduce current and v oltage distortions, achie ving a decrease in total harmonic distortion (THD) from o v er 55% to less than 5%. Another study [4] e xplored reacti v e po wer control on the grid-side con v erter of a w a v e ener gy system to attenuate v oltage harmonics. A comprehensi v e re vie w [5] has also discussed the use of in v erter -based distrib uted generation units as acti v e po wer quality conditioners for harmonic compensation. Moreo v er , research in v olving indirect current control (ICC) combined with fuzzy logic control (FLC) demonstrated ef fecti v e harmonic reduction under highly nonlinear loads, maintaining compliance with IEEE 519-1992 standards [6]. Finally , studies on DFIG-based wind turbines ha v e critically analyzed harmonic reduction methods to enhance the quality of the current injected into the grid [7]. T ogether , these w orks highlight the need for more inte grated and adapti v e strate gies capable of addressing comple x harmonic proles in rene w able ener gy systems. Among J ournal homepage: http://ijpeds.iaescor e .com Evaluation Warning : The document was created with Spire.PDF for Python.
934 ❒ ISSN: 2088-8694 v arious generator congurations for wind ener gy con v ersion, doubly fed induction generators (DFIGs) are widely emplo yed because of their ef cienc y and controllability . Se v eral control strate gies ha v e been de v eloped, including sliding mode control, which of fers f ast response and high precision [8]–[10]. Modern wind ener gy systems are e xpected not only to deli v er acti v e po wer b ut also to pro vide ancillary services such as reacti v e po wer support and harmonic current mitig ation. V oltage uctuations and harmonic distortions can disrupt sensiti v e equipment and de grade po wer quality , quant ied by THD [11]. Numerous methods ha v e been proposed to reduce harmonics, including modied rotor -side con v erter (RSC) control, grid-side con v erter (GSC) adjustments, and e xternal acti v e lters [2], [12]–[17]. Despite these adv ances, a comprehensi v e strate gy capable of suppressing all harmonic components while maintaining the main objecti v es of the wind ener gy con v ersion system (acti v e po wer generation and reacti v e po wer compensation) is still lacking. T o address this g ap, this study proposes a harmonic m itig ation strate gy inte grating a mult i v ariable lter with sliding mode control of both RSC and GSC. The proposed approach ensures near -sinusoidal stator currents at the point of common coupling (PCC) under dif ferent load conditions [18]–[22], thereby enhancing o v erall po wer quality in DFIG-based wind ener gy systems connected to the grid. Compar ed to e xisting RSC–GSC harmonic mitig ation schemes, the proposed approach inte grates a multi v ariable lter with sliding mode control on both con v erters, enabling more rob ust suppression of multiple harmonic components under highly nonlinear and unbalanced load conditions. Unlik e con v entional PI-based methods or standalone APFs, our method ensures near -sinusoidal stator currents at the PCC without compromising acti v e and reacti v e po wer control. The remainder of this paper is or g anized as follo ws: Section 2 presents the system modeling, including the DFIG conguration and l oad representation un de r linear , nonlinear , balanced, and unbalanced conditions. Section 3 details the harmonic current identication methods and introduces the proposed mitig ation strate gies. Section 4 discusses the simulation setup and results, highlighting performance analysis and observ ed limitations. Finally , section 5 concludes the paper and outlines future research directions. 2. SYSTEM MODELING AND METHODOLOGY 2.1. T opology of the studied system Currently , v ariable-speed wind systems based on the DFIG are the most widely used technology in onshore wind f arms. Their main adv antage lies in the f act that the static con v erters are sized for only a fraction of the nominal po wer of the DFIG, as the y are connected to the grid through the rotor winding. The o v erall conguration of the studied system is illustrated in Figure 1. It consists of the wind ener gy con v ersion system that supplies v arious types of loads, including linear , non-linear , balanced, and unbalanced loads. Figure 1. Block diagram of wind ener gie con v ersion system Int J Po w Elec & Dri Syst, V ol. 17, No. 2, June 2026: 933–945 Evaluation Warning : The document was created with Spire.PDF for Python.
Int J Po w Elec & Dri Syst ISSN: 2088-8694 ❒ 935 2.2. DFIG modeling Starting from the schematic representation of a DFIG in the reference frame of three phases, as wi d e ly presented in [23]–[26], and adopting the assumptions that the stator resistance R s is ne gligible (which is reasonable for higher po wer le v els) and that the stator ux φ s is constant (assuming a constant st ator v oltage V s ) and oriented along the dq axis, the machine equations can be e xpressed as (1)–(4). V sd = 0 V sq = V s = ω s φ s V r d = R r I r d + dφ r d dt − ω r φ r q V r q = R r I r q + dφ r q dt + ω r φ r d (1) and: φ sd = φ s = L s I sd + M I r d 0 = L s I sq + M I r q φ r d = L r I r d + M I sd φ r q = L r I r q + M I sq (2) The stator currents are gi v en by the follo wing system, as (3). I sd = φ s L s − M L s I r d I sq = − M L s I r q (3) The acti v e and reacti v e po wers become (4). P s = V sq I sq = − M L s V s I r q Q s = V sq I sd = V s φ s L s − M V s L s I r d (4) The pre vious equations describe the dynamic beha vior of the DFIG under the assumptions of ne gligible stator resistance and constant stator ux oriented along the dq-axis. This mathematical model forms the foundation for analyzing the generator performance and its interaction with the electrical netw ork. In practical applications, the DFIG supplies v arious types of load, which can be linear or nonlinear , balanced, or unbalanced. Accurate modeling of these loads is essential to e v aluate their impact on po wer quality , particularly harmonic distortions. The ne xt section presents the modeling approaches for the loads connected to the system. 2.3. Load modelling Since wind turbines are connected to the distrib ution grid, t he y are often located clos e t o poll uting loads that inject harmonics into the netw ork. The load is connected to the wind ener gy con v ersion system via the point of common coupling, as sho wn in Figure 1. T w o types of loads are considered: i) Linear loads: which may be inducti v e and/or resisti v e, consuming acti v e and/or reacti v e po wer; ii) Nonlinear loads: represented here by a three-phase diode bridge rectier supplying a direct current (DC) load, which can also ha v e inducti v e and resisti v e components. If the load v alues are identical across the three phases, the load is considered balanced; otherwise, it is unbalanced. A preliminary test w as conducted to v alidate the modeling of balanced and unbalanced loads. The corresponding current w a v eforms are sho wn in Figure 2. At time t = 500 ms, a v ariation in the acti v e and reacti v e po wer of the loads is imposed in order to increase the THD, with the aim of highlighting the proposed solution for the con v erter system’ s contrib ution to harmonic mitig ation. T o a v oid o v erloading the article with gures, spectral results for all cases are summarized in T able 1, including THD and the percentage of the main harmonic components. The high v alue of the DC component is mainly due to the nonlinear nature of the load. As observ ed in Figure 2, a DC component appears in balanced and unbalanced load conditions, e xplains the asymmetry of the w a v eforms with respect to the time axis. Impr o ved contr ol str ate gy for harmonic curr ent mitigation in DFIG-based wind turbines ... (Hind Elaimani) Evaluation Warning : The document was created with Spire.PDF for Python.
936 ❒ ISSN: 2088-8694 2.4. Simulation of the wind ener gy system in the pr esence of harmonic-polluting loads T o highlight the performance of the wind ener gy system in the presence of electrical loads, the simulation of the con v ersion system connected to the grid through the PCC w as carried out. On the other side, the PCC is connected to harmonic-polluting loads, as illustrated in Figure 1. The simulations produced the results sho wn in Figure 3. The results of the spectra of the currents injected into the grid I g are summarized in T able 2. Based on these results, it is observ ed that the presence of the wind ener gy system w orsens the situation: in f act, the THD increases and the grid current becomes more distorted. Therefore, a ltering solution is essential. Figure 2. Three-phase current responses for balanced and unbalanced load cases T able 1. Summary table of the THD of load currents Frequenc y (Hz) I cbalanced I cunbalanced t = 100 ms t = 500 ms t = 100 ms t = 500 ms I ca I cb I cc I ca I cb I cc 0 86 217 86.88 154 104 217 386 2622 50 100 100 100 100 100 100 100 100 300 5.05 12.63 5.05 8.99 6.10 12.63 22.46 15.24 600 1.4 3.5 1.40 2.49 1.69 3.5 6.23 4.23 900 0.64 1.59 0.64 1.13 0.77 1.59 2.83 1.92 THD (%) 5.31 13.26 5.31 9.44 6.40 13.26 23.59 16 1 1.05 1.1 1.15 1.2 0 0.5 1 I g B a l a n c e d (PU) Balanced Load 5 5.05 5.1 5.15 5.2 0.4 0.6 0.8 1 Balanced Load 1 1.05 1.1 1.15 1.2 Time(s) 0 0.5 1 I g U n b a l a n c e d (PU) Unbalanced Load 5 5.05 5.1 5.15 5.2 Time(s) 0.4 0.6 0.8 1 Unbalanced Load Figure 3. The currents injected into the grid to which the wind turbine and the loads are connected Int J Po w Elec & Dri Syst, V ol. 17, No. 2, June 2026: 933–945 Evaluation Warning : The document was created with Spire.PDF for Python.
Int J Po w Elec & Dri Syst ISSN: 2088-8694 ❒ 937 T able 2. Summary table of the THD of load currents Frequenc y (Hz) I g balanced I g unbalanced t = 100 ms t = 500 ms t = 100 ms t = 500 ms I g a I g b I g c I g a I g b I g c 0 146.48 366.18 146 73.61 152.12 366.19 350 380 50 100 100 100 100 100 100 100 100 300 8.52 21.3 8.52 45.54 8.85 21.3 13.85 22.12 600 2.36 5.91 2.36 12.36 2.45 5.9 11.57 6.13 900 1.07 2.69 1.07 5.75 1.12 2.69 4.37 2.79 THD (%) 8.95 22.36 8.95 47.8 9.29 22.36 31.24 23.23 3. HARMONIC MITIGA TION When the wind ener gy system w as connected to a distorted grid, the line current I g abc e xhibited harmonic frequenc y components of v arious orders, not limited to the 6th harmonic. In most pre vious studies, control strate gies tar geted only a single harmonic order , which w as then used to modify the DFIG con v erter control. In contrast, the control strate gy de v eloped in this w ork c on s iders all signicant harmonic components present in the load current I cabc . This comprehensi v e approach allo ws for a more accurate compensation under both balanced and unbalanced conditions. 3.1. Harmonic curr ent identication Se v eral harmonic identication techniques ha v e been reported in the literature. The m ost class ical one, widely used in acti v e po wer lter control, i s the instantaneous po wer (PQ) theory , originally proposed by Akagi. It i s based on the Concordia transformation, applie d to phase-to-neutral v oltages V sabc and load currents, to compute instantaneous acti v e and reacti v e po wers. These po wers can be decomposed as (5). ( P = P + e P Q = Q + e Q (5) The DC components P and Q correspond to the fundamental components and are e xtracted using lo w-pass lters. The A C parts e P and e Q are then obtained by subtracting these DC components, allo wing the harmonic currents generated by nonlinear loads to be identied. Another widely used technique is based on the synchronous reference frame (SRF) method, introduced by Bhattacharya and illustrated in [27]. Lik e the PQ method, it be gins with the Concordia transformation applied to the load currents, follo wed by a P ark transformation that projects them onto the rotating dq frame. In this frame, the fundamental component appears as a DC term, while harmonic components manifest as A C terms. A simple band-pass lter can then isolate the fundamental component. The SRF method presents se v eral adv antages: it is immune to v oltage harmonics and requires only tw o current sensors to identify all harmonic components of the nonlinear load. Ho we v er , in its classical form, it does not permit the e xtraction of a specic harmonic order . In this w ork, a multi-v ari able lter (MVF) is emplo yed for harmonic e xtraction, as described in [14]. The MVF enables the isolation of either the complete harmonic spectrum or a specic harmonic order , including both direct and in v erse sequence components. Its transfer function is e xpressed as (6). H ( s ) = Y s Y e = k s + k 2 + j ω c s 2 + 2 k s + k 2 + ω 2 c (6) Where: ω c : characteristic pulsation of the lter (corresponding to the tar geted frequenc y); k : positi v e constant controlling bandwidth and selecti vity; Y e : input signal to be ltered; and Y s : output signal ltered at the selected frequenc y . The cutof f angular frequenc y of the lter , denoted ω c , is dened as (7). ω c = εnω f (7) Where n represents the order of the signal component to be ltered, ε characterizes the type of component (direct or in v erse), and K is a posi ti v e constant. A Bode diagram of the selecti v e lter w as generated to analyze the ef fect of dif ferent v alues of the parameter K . It can be observ ed that increasing K reduces the lter’ s selecti vity , resulting in a wider Impr o ved contr ol str ate gy for harmonic curr ent mitigation in DFIG-based wind turbines ... (Hind Elaimani) Evaluation Warning : The document was created with Spire.PDF for Python.
938 ❒ ISSN: 2088-8694 bandwidth. In this case, instead of obtaining a signal containing a single frequenc y , the ltered signal e xhibits additional components, introducing noise. Ho we v er , the dynamic response of the o v erall system must also be considered, particularly re g arding the stability of the system. According to F ourier’ s theory , an y periodic signal can be e xpressed as a sum of sinusoidal components at multiples of its fundamental frequenc y . T o isolate harmonics, it suf ces to remo v e the fundamental component. Based o n frequenc y analysis of the current from balanced loads (see T able 1), and ne glecting harmonics abo v e 1 kHz, the current in phase a can be e xpressed as (8). I c ( t ) = A 0 + A sin(2 ω t + φ 1 ) + A 1 sin(12 ω t + φ 2 ) + A 2 sin(24 ω t + φ 3 ) + A 3 sin(36 ω t + φ 4 ) (8) After remo ving the fundamental component, the harmonic current becomes (9). I c har ( t ) = A ′ 0 + A ′ 1 sin(12 ω t + φ 2 ) + A ′ 2 sin(24 ω t + φ 3 ) + A ′ 3 sin(36 ω t + φ 4 ) (9) 3.2. Pr oposed harmonic mitigation strategies T w o complementary harmonic mitig ation strate gies ha v e been considere d for DFIG-based wind ener gy systems supplying nonlinear loads. Both approaches ha v e been indi vidually tested and e v aluated in pre vious w orks. In this study , a third strate gy is proposed as a combination of the tw o, aiming to enhance o v erall performance: i) RSC-based compensation: In this approach, RSC control is modied by injecting specic harmonic components into rotor current reference, thereby reducing their propag ation into stator current [14], [15]. ii) FSC-based acti v e ltering: Here, t he the full-s cale con v erter (FSC) operates as an act i v e lter tha t e xtracts and compensates for the harmonic components present in the measured grid currents [13], [16]. iii) Combined adapti v e strate gy: This enhanced method mer ges the adv antages of the pre vious tw o. It introduces an adapti v e adjustment block that ensures the DFIG maintains its primary objecti v es—acti v e and reacti v e po wer control—while achie ving impro v ed harmonic mitig ation [23], [24]. 3.2.1. RSC contr ol modication f or harmonic curr ent injection Dif ferent control techniques can be applied to po wer con v erters. Among them, PI-bas ed control remains the most commonly used due to its simplicity , whereas adv anced nonlinear techniques such as backstepping or sliding mode control pro vide superior performance in terms of dynamic response and po wer quality . In this w ork, sliding mode control is applied to both con v erters, as e xtensi v ely de v el oped in [23], [24]. Based on the mathematical models of the generator , DC b us, and grid lter , control la ws ha v e been deri v ed to manage both the RSC and the GSC. The RSC controller is mainly responsible for ensuring that the acti v e and reacti v e po wers follo w their respecti v e references. In the modied v ersion of the RSC control, the same fundamental control structure is preserv ed, b ut an additional term is introduced to eliminate the 6th-order harmonic. This is achie v ed by injecting the corresponding harmonic current into the rotor current reference used within the control loop. According to the DFIG model presented in the modeli ng section, under stator ux orientation (aligned with the d-axis), acti v e and reacti v e po wer control requires computing the rotor current, see in (4), from which the v oltage references are deri v ed. In steady-state operation, the DFIG inherently couples the stator and rotor currents, acting as a current amplier . Consequently , the harmonic components present in the load are not onl y incorporated into the control strate gy b ut also amplied to ef fecti v ely compensate for the harmonic distortion observ ed at the point of rene w able resources (PRR). The harmonic components of the rotor current references are obtained as (10). i r dh = L s M · L m i cdh i r q h = L s M · L m i cq h (10) Thus, the full e xpressions of the rotor current references are gi v en by (11). I ref r q = − L s V s · M · P ref s L s M · L m + i cq h I ref r d = V s ω s · M − L s V s · M · Q ref s L s M · L m + i cdh (11) Int J Po w Elec & Dri Syst, V ol. 17, No. 2, June 2026: 933–945 Evaluation Warning : The document was created with Spire.PDF for Python.
Int J Po w Elec & Dri Syst ISSN: 2088-8694 ❒ 939 Once these updated rotor current references are computed, the corresponding reference v oltages are obtained using (1), as in the standard control structure. These v oltages are then applied to the RSC, which is controlled through pulse width modulation (PWM). Through this modication, the RSC act i v ely cancels the 6th-order harmonic component of the load current, as illustrated in Figure 4. The presence of harmonic components in the rotor v oltage can signicantly af fect the DFIG’ s int ernal beha vior . According to (1), these harmonics generate corresponding harmonic currents in the rotor circuit, which can then propag ate to the stator s ide. The frequenc y and sequence of these harmonics are dened by (3). Consequently , the induced imbalance between rotor and stator currents can lead to nonuniform magnetic loading, resulting in localized magnetic s aturation, e xcessi v e heating, and increased copper and iron losses. These ef fects ultimately reduce the o v erall ef cienc y and operational lifetime of the DFIG. Furthermore, according to (4), the mismatch between the generated and reference po wer components may indicate a loss of tracking accurac y in the initial control structure. T o mitig ate these ef fects and m aintain po wer control precision, a renement of the rotor current references is therefore required. Figure 4. Modied RSC control via sliding mode for harmonic mitig ation 3.2.2. FSC-based acti v e ltering f or harmonic compensation The second harmonic mitig ation strate gy relies on a dedicated acti v e lter (AF) implemented through a shunt con v erter , the full-scale con v erter (FSC), which has a structure similar to the RSC and GSC used in the DFIG-based wind ener gy con v ersion system as illustrated in Figure 1. The main di stinction lies in the control technique. While the RSC and GSC are dri v en by PWM , the FSC is controlled using a h ysteresis current control method. This enables rapid and precise tracking of the harmonic components e xtracted from the load current. The FSC is connected in parallel with the load and is e xclusi v ely responsible for compensating the isolated harmonic components obtained using the harmonic e xtract ion method described earlier . By injecting the appropriate compensating currents into the grid, this approach ef fecti v ely reduces the THD at the PCC. The FSC-based acti v e ltering is particularly ef cient in mitig ating multiple harm o ni c orders simultaneously and dynamically adapts to v ariations in load conditions. It ensures harmonic compensation without af fecting the primary acti v e and reacti v e po wer deli v ered by the DFIG. Impr o ved contr ol str ate gy for harmonic curr ent mitigation in DFIG-based wind turbines ... (Hind Elaimani) Evaluation Warning : The document was created with Spire.PDF for Python.
940 ❒ ISSN: 2088-8694 3.2.3. Combined generator -and grid-side harmonic mitigation The combi ned strate gy mer ges the tw o pre viously discussed approaches. The RSC is modied to inject harmonic components directly into the rotor current reference, while a parallel FSC-based acti v e lter simultaneously injects compensating currents into the grid (Figure 5). This dual-action strate gy allo ws harmonics to be mitig ated at tw o le v els: internally through the generator control and e xternally via the acti v e lter . Such an approach enhances o v erall harmonic suppression and ensures that the DFIG’ s primary objecti v es—acti v e and reacti v e po wer re gulation—are maintained. 3.2.4. Enhanced method of the RSC modication The adapted control strate gy must ensure harmonic current mitig ation while maintaining the acti v e po wer control of the DFIG. It is essential to emphasize that harmonic compensation should ne v er compromise the acti v e po wer output of the wind turbine, especially under f a v orable wind conditions that allo w for nominal po wer generation. Therefore, a modication of the rotor current references is implemented at the RSC le v el, prioritizing the re gulation of acti v e po wer production. The core idea lies in limiting the reference currents according to the o wchart illustrated in Figure 6, which ensures that harmonic compensation remains ef fecti v e without de grading the primary function of the wind ener gy con v ersion system. The rotor currents are rst calculated at their maximum v alues. The harmonic currents of the rotor are then analyzed to determine the reference currents, which are used to calculate the reference v oltages of the modulator’ s pulse width. The adjustment mechanism is illustrated in Figure 7. Blocks 1 and 2 illustrated in Figure 7 are composed as (12)–(14). V C C Gq - E q ui = − L s L r σ M V s ˙ P ref s + R r I r q + g ω s L r σ I r d + g M V s L s (12) V C C Gd - E q ui = L r σ V s ω s M − L s V s M ˙ Q ref s + R r I r d − g ω s L r σ I r q (13) V C C Gq = − L s L r σ M V s ˙ P ref s + R r I r q + g ω s L r σ I r d + g M V s L s + L r σ v 1 sgn( s ( P )) (14) Figure 5. Combined RSC and FSC-based harmonic mitig ation for a DFIG system Int J Po w Elec & Dri Syst, V ol. 17, No. 2, June 2026: 933–945 Evaluation Warning : The document was created with Spire.PDF for Python.
Int J Po w Elec & Dri Syst ISSN: 2088-8694 ❒ 941 Figure 6. Flo wchart of the reference current adjustment Figure 7. Block diagram of the modied RSC for harmonic mitig ation inte grating the current reference recalculation block 4. EV ALU A TION OF THE CONTR OL STRA TEGY 4.1. Simulation r esults The simulations were conducted to e v aluate the v alidity and ef fecti v eness of the proposed control strate gy . A 1.5 MW DFIG model w as de v eloped in MA TLAB/Simulink. Re g arding the load conditions, both balanced and unbalanced loads are considered. Before 500 ms, the linear load consumes 500 kW of acti v e po wer and 800 kV AR of reacti v e po wer , while the nonlinear load absorbs 90 kW and 1.2 MV AR. After 500 ms, the linear load remains unchanged with 500 kW and 800 kV AR, whereas the nonlinear load increases to 500 kW and 3 MV AR. T o isolate the inuence of harmonic mitig ation and clearly observ e the control dynamics, the system w as simulated under x ed wind speed conditions. This approach eliminates additional harmonics that could arise from wind speed uctuations. The simulation duration w as set to 600 ms and included both balanced and unbalanced load scenarios. In each case, linear and nonlinear loads were applied. A step change in acti v e and reacti v e po wer w as also introduced to increase the THD and e v aluate the control system’ s rob ustness. Impr o ved contr ol str ate gy for harmonic curr ent mitigation in DFIG-based wind turbines ... (Hind Elaimani) Evaluation Warning : The document was created with Spire.PDF for Python.
942 ❒ ISSN: 2088-8694 4.2. Discussion of r esults T o streamline the analysis and emphasize the performance of the proposed strate gy , the discussion focuses on the THD of k e y currents ( I r , I s , I c , and I g ) under the most se v ere condition—unbalanced loading. The simulation results yielded the current w a v eforms sho wn in Figure 8, while the acti v e and reacti v e po wer proles are presented in Figures 9 and 10. Figure 11 illustrates the DC-link v oltage, which remains stable throughout the simulation, conrming the proper ener gy balance and rob ustness of the propo s ed control scheme. T able 3 summarize the spectral analysis THD of the three-phase currents. 1 1.05 1.1 1.15 1.2 -1 0 1 I s (PU) 1 1.05 1.1 1.15 1.2 -1 0 1 I r  (PU) 1 1.05 1.1 1.15 1.2 Time(s) -1 0 1 I g (PU) 5 5.05 5.1 5.15 5.2 -1 0 1 5 5.05 5.1 5.15 5.2 -1 0 1 5 5.05 5.1 5.15 5.2 Time(s) -1 0 1 Figure 8. The currents of WECS under unbalanced load with adjustment block Similar to the pre viously proposed method, harmonic compensation is successful ly achie v ed. Ho we v er , the major impro v ement introduced by the adjustment block lies in preserving the primary ener gy con v ersion function of the wind system. Figures 9 and 10 sho w that the acti v e po wer accurately follo ws its reference deri v ed from the mechanical subsystem. Moreo v er , the rotor currents remain undistorted e v en under unbalanced load conditions, thus pre v enting potential operational issues in the DFIG. 0 1 2 3 4 5 6 Time(s) -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 P(PU) Active Power P r e f P Figure 9. The acti v e po wer of WECS under unbalanced load with adjustment block Int J Po w Elec & Dri Syst, V ol. 17, No. 2, June 2026: 933–945 Evaluation Warning : The document was created with Spire.PDF for Python.