Counter-rotating Wind Turbine Research Articles

Experimental investigation of the wake replenishment mechanisms of paired counter-rotating vertical-axis wind turbines

The understanding of wake recovery mechanisms is crucial for the design of efficient wind farm layouts and the development of accurate wake models. Recently, placing two vertical-axis wind turbines (VAWTs) in close proximity has demonstrated potential for increased power output. In this study, wind tunnel experiments were conducted to investigate the wake replenishment mechanisms behind paired VAWTs. The experimental campaign included testing an isolated VAWT and paired counter-rotating VAWTs. By combining qualitative observations of key flow field variables with a quantitative analysis based on momentum conservation, this study aims to enhance our understanding of the mixing mechanisms supporting the reintroduction of streamwise momentum into the wake of paired VAWTs. This research also involves a comparison of these mechanisms with those observed in the wake of a standalone VAWT. The results show that the differences between isolated and paired VAWTs in overall wake characteristics are minimal. The increased lateral advection within the wake of the isolated VAWT is offset by the enhanced vertical advection in the paired configuration, as a result of the change in the direction of cross-stream velocity within the gap between the paired VAWTs, which promotes a shift towards vertical flow rather than lateral flow.

Design and comparative analysis of dual rotor wound field excited flux switching generator for household DC microgrid system with rooftop wind turbine

In this paper, two variants of the magnetless dual rotor wound field excited flux switching generator (DRWFEFSG) are comparatively analyzed for single rotor wind turbine (termed as machine I (MI)) and counter rotating wind turbine applications (termed as machine II (MII)) for household direct current (DC) microgrid system. First, design concept and integration to wind turbine system are discussed. Secondly, comprehensively performance analysis i.e., static analysis, dynamic load/speed analysis and electromagnetic performance analysis are executed. Finite element analysis (FEA) based static analysis evident that MI offers 7.6% higher torque in inner rotor whereas MII exhibits 18% higher torque in outer rotor. Dynamic respond unveils that in comparison to MII, MI suffers from the issue of voltage regulation. Additionally, electromagnetic analysis reveals that both MI and MII exhibits excellent response under variable field Magneto-motive force (MMF). Comparative analysis unveils that MII requires lower field MMF to achieve same response to counterpart MI. Quantitative analysis divulge efficiency of 88.49% and power factor of 0.93 in MI whereas MII at rated operating point demonstrates 85.9% efficiency and 0.96 power factor. Finally, effectiveness of the study and validity of DRWFEFSG for wind turbine applications are tested with hardware prototypes of both MI and MII that fairly matched with FEA results.

Magnetic Coupling Effect and Performance Analysis of Dual Rotor Permanent Magnet Flux Switching Generator for Counter Rotating Wind Power Generation

To eliminate slip rings, brushes, and terminate gear-box mechanism, ferrite permanent magnet (PM) based counter rotating dual rotor PM flux switching generator (CRDRPMFSG) for direct drive counter rotating wind turbine (D <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> CRWT) application is proposed in this paper. Initially, the mechanism of gearless and brushless counter rotating wind power generation is discussed, and a simplified formulation opted for the slot/pole combinations. The proposed CRDRPMFSG encapsulate inner and outer machines with circumferentially magnetized PM enclosed by non-overlapped armature windings; thus, offering reduced overhang with compact design. However, co-axially linking the inner and outer machines through a shared stator yoke results in serious issues of magnetic coupling due to dual air-gap fields. To this end, eight topologies with various slot/pole combinations are comprehensively investigated using finite element analysis (FEA) for magnetic coupling effects and its influence on electromagnetic performance. From the analysis, it is shown that magnetic coupling level influence electromagnetic performance i.e., average torque, ripple rate, power factor, efficiency, losses, and output power. Moreover, it is noted that coupling level can be reduced by adopting same stator teeth in inner and outer machines or same stator teeth with different rotor poles. Finally, the predicted FEA calculations are verified experimentally with four benchmarked CRDRPMFSG prototypes.

Cross-coupling control design of a flexible dual rotor wind turbine with enhanced wind energy capture capacity

In order to improve the reliability of wind turbine grid connection and reduce the cost of wind power generation, this paper studies a counter-rotating dual rotor wind turbine (DRWT) which consists of decoupled driven-train subsystems, a triple-terminal converter and a dual rotor generator. For this new-type wind energy conversion system, its modeling and control strategy need to be studied. Firstly, mechanism model of the DRWT with a new structure is constructed. By investigating the effects of pitch angles and rotor speeds on output power, respectively, the maximum power output condition of the DRWT is obtained. Considering the overall energy conversion efficiency and mechanical load constraints, the optimal regime of the DRWT is established. Based on the optimal torque algorithm and cross-coupling control strategy, this paper presents a novel cross-coupling control strategy for the DRWT to track maximum power. The proposed strategy can regulate the rotor speed of the front and rear rotors, enabling DRWT to operate on the optimal speed combination curve. Finally, the hardware-in-the-loop experiment is built to test the performance of the proposed strategy under various wind conditions. The simulation results verify that the proposed strategy can improve power generation, and analysis shows that the proposed strategy fundamentally alters the energy capture ratio between the front and rear wind turbines to optimize total output power.

Comparison of Mixing Plane, Frozen Rotor, and Sliding Mesh Methods on a Counter-Rotating Dual-Rotor Wind Turbine

Nowadays, there are numerous new features available in CFD (computational fluid dynamics) that can simulate complex physical phenomena, which used to be challenging to address. However, in current CFD software, certain problems can be simulated using different approaches. In our article, we chose different rotating motion methods to analyze a counter-rotating dual-rotor wind turbine (CO-DRWT). Using the different rotating motion approaches we selected (mixing plane, frozen rotor, and sliding mesh), we examined the torque on the rotors and compared them. The following conclusion was reached. If transient fluid flow must be examined, then the sliding mesh method provided the most realistic results, while the frozen rotor method was adequate if we investigated the effect of wake and vortex near the rotating blades or on its environment. The mixing plane method should be used when the focus is on the kinetics and kinematics of the rotating blade or structure.

Comparative analysis of torque-adding wind energy conversion systems with a counter-rotating vs. conventional electric generator

The paper presents a comparative analysis on the steady-state behavior of two counter-rotating wind turbines with same components, where the generator can operate as a counter-rotating (with both a mobile rotor and stator—Case a) vs. conventional (with a fixed stator—Case b) electric machine. These wind energy conversion systems (WECSs) also have two coaxial counter-rotating wind rotors and a one-degree-of-freedom (1-DOF) planetary speed increaser with two inputs and one or two outputs for compatibility with the considered generator. The paper aims at highlighting the efficiency and energy performances of WECSs with a counter-rotating vs. conventional generator by investigating three functional scenarios (A, B, and C) of the two WECS cases (a and b) under the assumption of identical or different counter-rotating wind rotors. A generalized kinetostatic modeling algorithm is first proposed, starting from the general case of WECS with a counter-rotating generator, which allows the establishment of analytical relationships corresponding to speeds and torques at input and output shafts. Numerical simulations of the obtained closed-form model in each scenario highlighted the influence of the constructive parameters on WECS performances, as well as the energetic superiority of WECS, with a counter-rotating generator (Case a) vs. conventional generator (Case b): higher efficiency by 1.2% and more output power by 1% (Scenario A) to 5.5% (Scenario C).

Effect of the yaw angle on the aerodynamics of two tandem wind turbines by considering a dual-rotor wind turbine in front

The innovative dual-rotor counter-rotating wind turbine (CRWT) shows great importance in the development of offshore wind farms. In this paper, the performance and wake characteristics of the independent CRWT and two tandem wind turbines equipped with a CRWT at different yaw angles were numerically studied using the open-source software SOWFA (Simulator fOr Wind Farm Applications). The actuator line model (ALM) and large-eddy simulation (LES) were used to model wind turbines and turbulent flows. The third generation of vortex identification criterion was used to analyze wake vortex characteristics. The results indicated the auxiliary rotor had a negligible effect on the main rotor in terms of the dominant frequency and fluctuations. In comparison with the rotational blade frequency (BF), it was found that one BF and double BF were equivalent to the dominant frequency of the SRWT and CRWT, respectively. The CRWT suffers a greater velocity deficit and has a faster velocity recovery. In the case of tandem wind turbines, the upstream wind turbine equipped with a CRWT performs minimal influence on the optimal yaw angle of 30°. In addition, the effects of the yaw angle on wake center deflection, wake width, and performance fluctuation for the downstream wind turbine were investigated.

A Novel Dual Electrical and Dual Mechanical Wound Field Flux Switching Generator for Co-Rotating and Counter-Rotating Wind Turbine Applications

A Novel Dual Electrical and Dual Mechanical Wound Field Flux Switching Generator for Co-Rotating and Counter-Rotating Wind Turbine Applications

Comparative energy performance analysis of four wind turbines with counter-rotating rotors in steady-state regime

In the worldwide effort to decarbonize the electricity generation, increasing the energy performance of renewable energy conversion systems is a continuing global concern and challenge for stakeholders. In this context, the paper presents the results of a comparative study on energy performance of four counter-rotating wind turbines of different types. In this regard, the authors propose a new reconfigurable structure of a counter-rotating wind system, able of operating in four distinct cases: with traditional electric generator (with fixed stator) or counter-rotating generator, with monomobile (torque adding) or bimobile (speed adding) speed increaser. These functional cases are obtained by the appropriate command of two intermittent clutches. A generalized algorithm for kinematic and static analytical modeling of the reconfigurable wind system in steady-state regime is proposed in the first part. Also, a new approach for optimizing the main design parameters, such as the ratio of wind rotor diameters, is detailed. The numerical simulations of the obtained closed-form model, for optimized value set of design parameters and various wind speed values, showed a slight energy advantage of using counter-rotating generators and monomobile transmissions, but accompanied by drawback of increased complexity. The main results of the paper, i.e. the new reconfigurable wind system concept and its analytical steady-state model of speeds, torques and efficiency, are useful for researchers and practitioner interested in developing optimized counter-rotating wind turbines.

Effect of turbulence on the performance of a pair of vertical-axis wind turbines

The focus of this study is to investigate under high turbulence intensity the performance and wake characteristics of a pair of closely spaced counter-rotating vertical axis wind turbines (VAWTs) in wind tunnel-controlled conditions. To achieve this, wind tunnel experiments for an isolated VAWT and dual VAWTs are conducted. A squared-mesh wooden grid is placed upstream of the wind turbines to increase the level of free stream turbulence. The wind tunnel tests confirm the increase in power coefficient of paired VAWTs in turbulent flows compared to smooth flows. Additionally, this study analyses the near-wake downstream of the paired turbines in both smooth and turbulent flows to better understand the flow physics.

Development of a Dual-Input Magnetic Gear Train for the Transmission System of Small-Scale Wind Turbines

Magnetic gear mechanisms have advanced to have a promising future in transmission technology. Previous research indicates that magnetic gear mechanisms might replace mechanical gear mechanisms in some applications. Small-scale wind turbines (SWT) with counter-rotating rotors that were initially fitted by bevel gears are proposed to be replaced by a coaxial magnetic gear train (CMGT). The CMGT is intended for use as a speed multiplier in order to obtain maximum power at low wind speeds, due to its beneficial transmission of power without physical contact. The primary objective of this study is to build a dual-input CMGT that will be employed in the transmission system of small-scale counter-rotating wind turbines. A dual-input CMGT is built through the analytical modeling of an equivalent magnetic circuit (EMC), which aims to predict the magnetic flux density in the air-gaps of CMGT. Several models within design constraints were compared to obtain the optimum design parameters of the preliminary CMGT design resulting from an EMC analysis. The optimized critical design parameters were then selected and analyzed using finite-element analysis (FEA) to depict the performance of the proposed SWT design. According to the findings, the developed design can generate an inner air-gap flux density of 0.8314 T and an outer air-gap flux density of 1.0200 T. The model likewise produces promising simulation results with an output transmitted torque in the inner rotor (output link) of 8.7 Nm, 56.9 Nm in the outer rotor, and 48.0 Nm in the carrier with pole-pieces. Thus, this design can generate higher torque than a bevel-geared wind turbine. The speed characteristics are also compromised in order to raise the generator’s rotating speed to generate more power. Finally, this study demonstrates the performance and embodiment design of the proposed SWT using CMGT.

Dual mechanical port power distribution in dual rotor permanent magnet flux switching generator for counter‐rotating wind turbine applications

The cover image is based on the Research Article Dual mechanical port power distribution in dual rotor permanent magnet flux switching generator for counter-rotating wind turbine applications by Wasiq Ullah et al., https://doi.org/10.1049/rpg2.12450.

Increasing energy efficiency of counter-rotating wind turbines by experimental modelling

With the significant advance in exploiting wind energy, there has been a shift in research from the study of conventional systems to the study of counter-rotating systems due to additional energy input of the second rotor. The paper presents the results of the research on achieving an increase in the energy efficiency of counter-rotating wind power conversion systems. For this purpose, there have been designed different sizes of wind rotors, were 3D printed and tested in an open-circuit aerodynamic tunnel for different wind velocities and axial distances between rotors. The constructive design consisting of a smaller diameter front rotor and a larger rear rotor was chosen. The individual wind rotors were used to configure two experimental models of counter-rotating wind systems. The testing results analysis and interpretation enabled the establishing of the design and operating conditions that provide the highest power extracted from wind at 10 m/s velocity. A higher efficiency of the wind turbine system is achieved for a lower ratio between the front and rear turbines. In the case of the analysed experimental models, an increase in system efficiency of 49.14% is achieved for a 0.845 diameter ratio, and of 39.02% for 0.945 diameter ratio, respectively.

Effect of Rotor Topology on the Performance of Counter-Rotating Double-Sided Flux Switching Permanent Magnet Generator

Recently, electric power generation from direct-drive counter-rotating wind turbine has gained considerable attention. Consequently, employing an efficient and a high power density electric generator is important. In this regard, flux switching permanent magnet generator with double-sided structure is one of the potential candidates for this purpose due to its features like inherently magnetic gearing effect, high power density, high reliability, and robust rotor structure. In this regard, rotor structure of double-sided flux switching permanent magnet generator is one of the most important factors which can highly affect the machine's performance due to the fact that, rotor geometry is the main part in the flux switching procedure of double-sided flux switching permanent magnet generator. Consequently, this paper presents a comprehensive analysis of counter-rotating double-sided flux switching permanent magnet generator with segmented rotor and laminated rotor in which a bridge is located between adjacent rotor poles. The finite element simulations and experimental tests results showed that the proposed generator with laminated rotor gained from the higher power density in comparison with the segmented one whereas in the case of segmented rotor, the torque ripple is lower.

A Comparative Study of Dual Stator With Novel Dual Rotor Permanent Magnet Flux Switching Generator for Counter Rotating Wind Turbine Applications

Compared with the single rotor wind turbine, a counter-rotating (CR) wind turbine with two rotor sets leads to twice power density. In this regard, dual stator CR (DSCR) permanent magnet flux switching generator (DSCR-PMFSG) is employed. However, in DSCR-PMFSG both rotor and armature parts are rotating and require slip rings for power transmission. These slip rings associate demerits of constant maintenance, poor speed regulation, increased cost, and additional slip ring losses, whereas DSCR-PMFSG offer lower flux and lesser power density. To overcome the demerits of DSCR-PMFSG as mentioned earlier, this paper proposed a novel dual rotor counter-rotating permanent magnet flux switching generator (DRCR-PMFSG) for wind turbine applications that eliminate the requirements of slip rings and retain brushless operation. The proposed DRCR-PMFSG share one stator connected back-to-back through a flux bridge that provides an alternate flux path between two mechanical ports associated with the inner rotor and outer rotor, contributing to the cumulative output. A detailed comparative analysis of DSCR-PMFSG and DRCR-PMFSG is performed under static characteristics, overload, and wide speed range to generate output power, voltage, current, power density, and efficiency. Quantitative comparative analysis under static analysis evident that proposed DRCR-PMFSG exhibits 33.29% higher flux, suppressed cogging torque and torque ripples up to 53.48% and 67.45%, respectively. Furthermore, a comprehensive quantitative analysis is performed under coupled overload and over-speed capability. Analysis exposes that in comparison with DSCRP-PMFSG, the proposed DRCR-PMFSG improves voltage regulation factor by 55.88%, output current enhanced by 67.9%, raise output voltage to 2.01 times, and power density to 1.72 times while maintaining the efficiency of 90.195% and achieving stable voltage profile with load variation. Finally, a detailed comparative analysis with conventional designs is performed and comprehensive mathematical modelling based on sub-domain model is developed accounting stator slot and rotor pole combinations, magnetic saturation, and winding configuration to validates finite element analysis (FEA) of JMAG Designer v.20.1.

A Comparative Performance Analysis of Counter-Rotating Dual-Rotor Wind Turbines with Speed-Adding Increasers

Increasing the efficiency of wind power conversion into electricity poses major challenges to researchers and developers of wind turbines, who are striving for new solutions that can ensure better use of local wind potential in terms of both feasibility and affordability. The paper proposes a novel concept of wind systems with counter-rotating wind rotors that can integrate either conventional or counter-rotating electric generators, by means of the same differential planetary speed increaser, aiming at providing a comparative analysis of the energy performance of counter-rotating wind turbines with counter-rotating vs. conventional electric generators. To this end, a generalized analytical model for angular speeds and torques has been developed, which can be customized for both system configurations. Three numerical simulation scenarios have been contrasted: (a) a scenario with identical wind rotors in both systems, (b) a scenario with the secondary wind rotors being identical in the two applications, but different from the primary rotors, and (c) a scenario with different secondary rotors in the two wind turbines. The results have shown that the wind systems with counter-rotating generator are more efficient and have a higher amplification ratio, compared to systems with conventional generators. In addition, the analyzed wind system with a counter-rotating generator displays better energy performance with low values for output power and ratio of input speeds, whereas the wind turbine with a conventional generator proves to be more efficient in the high-value range of the above-mentioned parameters.

Aerodynamic Performance of Counter-Rotating Vertical Axis Wind Turbine

Aerodynamic Performance of Counter-Rotating Vertical Axis Wind Turbine

Using Adaptive Second Order Sliding Mode to Improve Power Control of a Counter-Rotating Wind Turbine under Grid Disturbances

This work presents a new control strategy for counter-rotating wind turbine (CRWT) driven doubly-fed induction generator (DFIG) under grid disturbances, such as unbalanced network voltage scenarios. The proposed strategy based on the power control used dynamic gains second order sliding mode control (SOSMC). The power control of a DFIG by SOSMC widely based on the super-twisting (ST) algorithm with invariable parameters and sign functions. The proposed control method consists in using dynamic-parameters ST algorithm that ensures a better result than a conventional strategy. The proposed control scheme used 2 sliding surfaces such as reactive and active powers to control them. Also, the sign functions are replaced by saturation (sat) functions in order to minimize the chattering problems. Simulation results depicted in this research article have confirmed the good usefulness and effectiveness of the proposed adaptive super-twisting algorithm of the CRWT system during grid disturbances.

Improved Vector Control of a Counter-Rotating Wind Turbine System Using Adaptive Backstepping Sliding Mode

The vector control (VC) method based on proportional-integral (PI) controllers of a doubly fed induction generator (DFIG) integrated in a counter rotating wind turbine (CRWT) system have many problems, such as low dynamic performances, coupling effect between the d-q axes and weak robustness against variation parametric. In order to resolve these problems, this research work proposes an adaptive backstepping sliding mode (ABSM) controller. The proposed control strategy consists in using dynamic-gains that ensures a better result than a conventional VC method. Stability of the proposed ABSM control approach has been proved by the Lyapunov method. Simulation results depicted in this research paper have confirmed the good usefulness and effectiveness of the proposed ABSM control.

Influence of the direction of rotation on the wake characteristics of closely spaced counter-rotating vertical-axis wind turbines

Closely spaced counter-rotating vertical-axis wind turbines (VAWTs) exhibit a considerable power improvement compared to the same turbines in isolation. It thus makes sense to study their potential for wind farm production optimisation. With this objective in mind, the wake of an isolated VAWT is compared experimentally to the wake of counter-rotating VAWTs. Because of the unsteady aerodynamics, the wake of an isolated VAWT deflects towards the region behind its upwind moving blade. The direction of rotation thus directly influences the deflection of the wake. For paired configurations, it is possible to use this wake deflection as an advantage. A pair of counter-rotating VAWTs where the upwind moving blades are at the centre of the pair, exhibits a particularly narrow wake. With the benefit of a power improvement and a narrow wake, closely spaced counter-rotating VAWTs exhibit promising characteristics to improve the power density in a wind farm.