Direct-drive Wind Turbine Research Articles

Design of fuzzy controller for direct drive wind turbines

Based on the research results of these years, this paper proposes a design of 3MW direct-driven wind generation inverter, and takes much effort in the control algorithm research and MATLAB simulation. Some wonderful results are obtained. All this may provide the reference for practical application. The fuzzy controllers are designed, based on fuzzy logic control theory, which can perfect control of wind generation system with no mathematic model. Models of permanent magnet synchronous generator (PMSG) and dual pulse width modulation (PWM) converter with their controllers are set by MATLAB/Simulink. In addition, experiments are made on the simulation platform of variable speed constant frequency (VSCF) wind power generation system. The behavior of dual PWM converter is demonstrated by simulations and experiment, and the control strategy is valid and correct.

New control method of a robust NPC converter for renewable energy sources grid connection

This paper presents a new control strategy for the three-level, neutral point clamped (NPC), voltage source converter. The converter can be used in many high-power renewable energy systems such as direct drive wind turbines and hybrid generating units. The developed control algorithm proposes an improved solution to balance DC bus intermediate voltages using space vector modulation (SVM) techniques. It aims to guarantee fault ride-through (FRT) capabilities of renewable energy plants equipped with multilevel converters. Since the main attention of this paper is the grid side converter control, the energy generating system was simplified to an equivalent variable current source. The grid side converter is connected to the grid through an LCL filter. Two controllers were developed to achieve grid currents regulation. The first controller is based on PI-regulation. In the second case, linear quadratic Gaussian (LQG) control is investigated. The control of DC bus voltage is achieved by PI-regulation. Performances of the two controllers and the improved modulation technique are compared and evaluated in terms of accordance with the grid connection requirements (GCR) including, low voltage ride-through capabilities, frequency variation and reactive power control.

Direct-Drive Contactless Wind Generator with Concentrated Winding

A clear trend has emerged in the field of wind power industry concerning the creation of low-, medium-, and even high-power direct-drive wind turbines without the use of gearboxes. Such generators are usually multipolar and mostly excited from permanent magnets. In the low-speed performance, multipolarity means a higher specific torque and reliability as well as lower operating costs, which in the case of high-speed generators is hindered by gearboxes. Multipolarity with a high specific torque can be achieved mainly through the use of permanent magnets of high-energy materials (such as NdFeB) and through design solutions for the armature winding. The authors compare two most common types of wind generator's armature windings: the distributed one, which contains a coil embracing several teeth, and the concentrated armature winding - with one coil for one stator tooth. The comparison (along with the experience in developing the wind turbines) shows that the con-centrated winding version has a number of advantages, the main of them being the multipolarity. This means that the generator with a concentrated winding can be more acceptable for the direct-drive wind turbines, is easier to make and simpler to operate. Another very important advantage of concentrated windings shown in this work

Structural analysis and optimisation of transverse flux permanent magnet machines for 5 and 10 MW direct drive wind turbines

ABSTRACTThe transverse flux permanent magnet generator offers high power density in terms of active mass. Two configurations of this machine topology (referred to as TFPM‐1 and TFPM‐2) are described, and optimised electromagnetic designs are presented. Direct drive generators require a significant support structure, which is designed to minimise the deflection into the air gap due to inherent electromagnetic attraction forces. The design of these structures is also dependant upon the generator topology. Structural design tools, which can be used in a design office environment, have been developed for the transverse flux machine and verified using commercial numerical modelling packages. Generic disc and arm structures are used. Only static analysis has been performed, but this does provide the designer with an estimate for more detailed design. A comparison of mass is made between the two transverse flux machines and a more conventional iron‐cored permanent magnet generator. The comparison shows that TFPM‐2 has the lowest total mass at 5 and 10 MW, but the conventional iron‐cored machine is lighter than TFPM‐1. Copyright © 2012 John Wiley & Sons, Ltd.

Meeting modern grid codes with large direct-drive permanent magnet generator-based wind turbines-low-voltage ride-through

Ambitious offshore wind energy targets continue to drive technological innovation, with the latest direct-drive permanent magnet generator-based wind turbines promising higher efficiency and availability. However, these machines have fixed rotor flux, provided by the magnets, which means that their voltage rises with speed. Further, high machine stator reactance leads to significant magnetic energy storage in the stator windings. Both these aspects provide new challenges for the power converter when designing to meet modern low-voltage ride-through requirements. This paper therefore proposes a novel control strategy, using a minimally rated chopper and dynamic brake resistor (DBR) integrated with the wind turbine's power converter, to help these systems to meet the demands of modern grid codes. This control method may allow the chopper and DBR to be rated at only 40% of a fully rated version. Despite only partially rating the DBR system, the control method minimizes the torsional oscillations in the drive train, thereby protecting the mechanical system. Copyright © 2011 John Wiley & Sons, Ltd.

Modelling and analysis of direct-driven permanent magnet synchronous generator wind turbine based on wind-rotor neural network model

A new practical way of modelling direct-driven permanent magnet synchronous generator (PMSG) wind turbines is proposed. The model emphasizes on the wind-rotor-to-PMSG-to-converter-to-grid system, which is the main energy flow system of the direct-driven wind turbine. In this article, a new wind-rotor back propagation neural network is proposed, which consists of a four-layer network and is used to describe the wind-rotor aerodynamic characteristics. According to the orthogonal experimental method, 1200 sets of wind-rotor aerodynamic data, which are calculated based on combining blade element momentum-modified theory with a dynamic stall model, are adopted as the sample data; and the wind-rotor neural network is trained using the Levenberg–Marquardt algorithm. Then, the coupling dynamic models of the wind-rotor and PMSG, and AC–DC–AC converter model are established, respectively; the control strategies for the generator-side and grid-side converters are constructed, too. The mechanical model, electric model, and control model are integrated into the whole simulation model, and the numerical simulation are carried out. The research results show that all the wind-rotor aerodynamic characteristics, electrical characteristics, and control characteristics can be obtained quickly and efficiently from the constructed model, and are helpful for optimization design and control for large-scale direct-direct PMSG wind turbines.

Unity Power Factor Control of a Direct-Driven Permanent Magnet Synchronous Wind-Power Generator Based on Three-Level Converter

Direct-driven permanent magnet synchronous generator (PMSG) has become an important research subject besides the double-fed induction generator. With the increasing of unit capacity, the study of topology of high power converters based on multi-level converter is attracting more and more attention. The study of vector control of the direct-driven permanent magnet synchronous wind turbines based on three-level converter is carried out in this paper. Based on the maximum wind-energy capture control of the PMSG, the unity power factor operation of PMSG is realized by controlling the d-axis current to zero in the generator-side converter. A detailed comparative study of two-level system and three-level system is conducted. The simulation results verify the validity of this algorithm.

Modeling and Experimental Study on Grid-Connected Inverter for Direct Drive Wind Turbine

This paper designs a dual topological structure of grid-connected inverter for high-power wind turbine, and introduces PWM converter's operational state. It establishes mathematical model of grid-side converter for wind turbine, then it puts forward the dual closed-loop vector control strategy of grid-side converter based on dq coordinate. The combination of the dual topological structure and decoupling control realize the functioning of high-power factor and two-way transmission of energy. Grid-side converter can stabilize DC side voltage during rapidly changed wind velocity which led to changes of output power in generator. Active or reactive output current can be adjusted independently. The hardware experiments and simulation results verify the feasibility of the proposed control scheme in both the high stability accuracy and excellent property of grid-connected.

Fault Diagnosis for Wind Turbines Based on Vibration Signal Analysis

Fault diagnosis is an important technical method to improve the safety index and economic effectiveness of wind turbines, it also provide support to advanced maintenance and design in wind power equipment. In this paper, we have done vibration testing on two wind turbines, one is in normal, the other is with faulty, and then carried on comparative analysis of vibration signal to the experimental data, finally designed a fault diagnosis method for direct-driven wind turbine generators.

Dynamic Torque Analysis of a Wind Turbine Drive Train Including a Direct-Driven Permanent-Magnet Generator

Mechanical interactions between a wind turbine and a direct-driven permanent-magnet synchronous generator (PMSG) are studied, and a model to analyze the system behavior is suggested. The proposed model can be applied to analyze the mechanical vibrations of direct-driven wind turbine installations both in steady state and in dynamic cases. The cogging torque and torque ripple of the PMSG are used as excitation sources in the mechanical model. Four different permanent-magnet rotor constructions are analyzed. It is shown that the maximum allowable value of the cogging torque of the direct-driven permanent-magnet wind generator in this case is 1.5%-2% of the rated torque even when the corresponding resonance frequency does not occur in the operational speed range of the wind turbine. Furthermore, it was noticed that the resonance caused by the excitation torque should occur at the lowest possible speed.

MW급 직접구동형 풍력터빈시스템을 위한 영구자석 동기발전기의 게인 스케쥴링 속도제어기에 대한 연구

This paper presents a new gain scheduling speed controller of permanent magnet synchronous generators(PMSG) for MW-class direct-driven wind turbine systems. The proposed gain scheduling speed controller performs the speed tracking at more than one operating point, and the first-order torque observer estimates the turbine torque which is needed to precisely control the speed of PMSG. The proposed speed controller verifies that the PMSG can successfully follow the reference speed which is determined via the maximum power point tracking(MPPT) control and pitch control under turbulent wind conditions. The proposed speed control algorithm is simulated using Simulink and its performance is confirmed through comparison with the results by PI control method.

Application of the ensemble empirical mode decomposition and Hilbert transform to pedestal looseness study of direct-drive wind turbine

The fault signal problems of wind turbine are non-linear and non-stationary, thus it is difficult to obtain the obvious fault features. In this study, a time-frequency method based on EEMD (ensemble empirical mode decomposition) and Hilbert transform is presented to investigate the bearing pedestal looseness fault of direct-drive wind turbine. The real vibration signals are analyzed using IMFs (intrinsic mode functions) extracted by ensemble empirical mode decomposition and Hilbert spectrum in the proposed method. The experimental results indicate that the proposed method is effective to extract the fault features of bearing pedestal looseness of wind turbine. And the results also demonstrate that fault features of front bearing pedestal looseness are different from rear bearing pedestal looseness with the same looseness gap. The fluctuation of rotational frequency increases with the occurrence of front bearing pedestal looseness fault, especially the half rotational frequency and high-frequency components, and the shaft orbit is complex. Besides, we found that when the rear bearing pedestal is loosen, the fluctuation of rotational frequency also increases, and the half rotational frequency component can be found. But for the high-frequency components, it is not obvious, and the shaft orbit is an approximate ellipse. Although the fault features of front and rear bearing pedestal looseness are obvious, the powers generated by wind turbine generator only change slightly.

Fault diagnosis of direct-drive wind turbine based on support vector machine

A fault diagnosis method of direct-drive wind turbine based on support vector machine (SVM) and feature selection is presented. The time-domain feature parameters of main shaft vibration signal in the horizontal and vertical directions are considered in the method. Firstly, in laboratory scale five experiments of direct-drive wind turbine with normal condition, wind wheel mass imbalance fault, wind wheel aerodynamic imbalance fault, yaw fault and blade airfoil change fault are carried out. The features of five experiments are analyzed. Secondly, the sensitive time-domain feature parameters in the horizontal and vertical directions of vibration signal in the five conditions are selected and used as feature samples. By training, the mapping relation between feature parameters and fault types are established in SVM model. Finally, the performance of the proposed method is verified through experimental data. The results show that the proposed method is effective in identifying the fault of wind turbine. It has good classification ability and robustness to diagnose the fault of direct-drive wind turbine.

Modeling and Experimental Study on Grid-Connected Inverter for Direct Drive Wind Turbine

This paper designs a dual topological structure of grid-connected inverter for high-power wind turbine, and introduces PWM converter's operational state. It establishes mathematical model of grid-side converter for wind turbine, then it puts forward the dual closed-loop vector control strategy of grid-side converter based on dq coordinate. The combination of the dual topological structure and decoupling control realize the functioning of high-power factor and two-way transmission of energy. Grid-side converter can stabilize DC side voltage during rapidly changed wind velocity which led to changes of output power in generator. Active or reactive output current can be adjusted independently. The hardware experiments and simulation results verify the feasibility of the proposed control scheme in both the high stability accuracy and excellent property of grid-connected.

10 MW Class Superconductor Wind Turbine Generators

High temperature superconductor (HTS) technology enables generators with one third the weight and one half the losses of conventional machines. These technologies enable a significant reduction in the size and weight of 10 MW-class generators for direct-drive wind turbine systems and reduce the cost of clean energy relative to conventional copper and permanent-magnet-based generators and gearboxes. With compact and light-weight 10 MW-class HTS generators, installation and low maintenance operation of high power wind turbine systems becomes practical and enable cost-effective access to wind resources. Under a program funded by the NIST-Advanced Technology Program, key generator technologies for a 10 MW class generator have been developed. This paper summarizes work under the NIST and internal programs.

Fatigue Life of Main Shaft Bearing of Direct Drive Wind Turbine

A calculation method of fatigue life for main shaft bearing of direct drive wind turbine was proposed. The statics models of the bearing were established and a set of equilibrium equations were obtained. By solving the equilibrium equations, the displacements of the inner ring were obtained, and the rolling element loads were calculated further. Based on the load distribution of the rollers, the fatigue life of the bearing was calculated and the influences of the clearances on it were researched. Results show that the clearances of the bearing can influence its service life distinctly. Zero axial clearance is recommended for the bearing.

Fault-Tolerant Control for a Modular Generator–Converter Scheme for Direct-Drive Wind Turbines

A modular power electronic converter, with a cascaded H-bridge multilevel inverter, has been proposed as the grid interface for a large direct-drive wind turbine generator. The present study is to investigate the potential and requirement of fault-tolerant operation in such a system. As each module is connected to isolated generator coils, tolerance to a module or coil fault is possible if the affected module can be bypassed, whereas the control of the healthy modules can be adjusted accordingly. A boost rectifier scheme on the machine side of the power conversion stage has been developed for this purpose, featuring control of the coil current without measuring the electromotive force. A coordinated dc-link voltage controller has been developed, which can rapidly raise the dc-link voltage of the remaining modules to compensate for the loss of a module while ignoring the ripple in the dc link due to low-frequency inverter switching. The ability of the resultant system to tolerate module faults has been demonstrated on a small-scale laboratory prototype.

Structural Flexibility: A Solution for Weight Reduction of Large Direct-Drive Wind-Turbine Generators

This paper looks into a new concept for reducing the structural weight of large direct-drive generators used in wind turbines. The concept uses magnetic bearings to position the rotor of the generator. The use of magnetic bearings allows structural flexibility in the generator. The weight of the rotor using the new concept is compared to the weight of a rotor designed with conventional methods. For a 5-MW generator, the result is that the structural weight of the rotor reduces by 45%.

Techno-Economic Comparison of Operational Aspects for Direct Drive and Gearbox-Driven Wind Turbines

The majority of wind turbines currently in operation have the conventional Danish concept design-that is, the three-bladed rotor of such turbines is indirectly coupled with an electrical generator via a gearbox. Recent technological developments have enabled direct drive wind turbines to become economically feasible. Potentially, direct drive wind turbines may enjoy higher levels of availability due to the removal of the gearbox from the design. However, this is only a theory: so far not substantiated by detailed analytic calculation. By providing such a calculation, this paper enables us to quantitatively evaluate technical and economic merits of direct drive and gearbox-driven wind turbines.

Operating capability as a PQ/PV node of a direct-drive wind turbine based on a permanent magnet synchronous generator

This paper describes the modelling and control system of a direct-drive PMSG wind turbine for effective active and reactive power generation control and voltage control at the grid connection point. This study focuses on the maximum power capability of the wind turbine, which is limited by its generator and power converter. The ability of this model and control strategy are assessed by means of simulations and discussed at length. The results of our study show that a PMSG wind turbine is able to actively participate in grid operation because it can independently control active and reactive power production (operating as a PQ node) or the active power and voltage at the connection node (operating as a PV node).