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A Fuzzy Logic Controller to Increase Fault Ride-Through Capability of Variable Speed Wind Turbines  [PDF]
Geev Mokryani,Pierluigi Siano,Antonio Piccolo,Vito Calderaro
Applied Computational Intelligence and Soft Computing , 2012, DOI: 10.1155/2012/405314
Abstract: A fuzzy controller for improving Fault Ride-Through (FRT) capability of Variable Speed Wind Turbines (WTs) equipped with Doubly Fed Induction Generator (DFIG) is presented. The controller is designed in order to compensate the voltage at the Point of Common Coupling (PCC) by regulating the reactive and active power generated by WTs. The performances of the controller are evaluated in some case studies considering a different number of wind farms in different locations. Simulations, carried out on a real 37-bus Italian weak distribution system, confirmed that the proposed controller can enhance the FRT capability in many cases. 1. Introduction Wind turbines (WTs) are typically located in remote and rural areas. In these areas, the feeders are long and operated at a medium voltage level characterized by a high R/X ratio and unbalanced voltage situations. Furthermore, weak grids are usually referred to have a “low short-circuit level” or “low fault level.” In a weak network a change in the real and reactive power can cause a considerable change in the voltage. The impact relies on the strength of the network and the output power of the WTs [1]. Integration of WTs into weak grids can cause the steady-state voltage level to go outside of its acceptable limit. Therefore, it can limit the exploitation of wind energy resources. Another constraint is related to the effect of the power generated by WTs on the voltage quality. Voltage level limitations and accurate control systems are required to control the voltage variations as well as to improve the voltage quality [2], and variable speed WTs can be used as reactive power sources for voltage control. In recent times, many researches have been carried out in this field. A proportional-integral- (PI-) based control algorithm to control the reactive power produced by WTs has been proposed in [3]. In [4], the authors have proposed a mathematical model of the Doubly Fed Induction Generator (DFIG) for the analysis of active and reactive power performances of a wind farm (WF). In [5], the relation between reactive and active power to maintain the DFIG’s operation inside the maximum rotor and stator currents has been studied. In [6], the authors have proposed a fuzzy controller to manage the operation of a Flywheel Energy Storage System (ESS) connected to the DC bus. Recently, the penetration of WTs into the grids increased, and the performance of the WTs under faults has became an important issue, especially for DFIGs. Several grid codes prescribed, in fact, that WTs should remain connected to the network during and
Improved Control Strategy for DFIG Wind Turbines for Low Voltage Ride Through  [PDF]
Zaijun Wu,Chanxia Zhu,Minqiang Hu
Energies , 2013, DOI: 10.3390/en6031181
Abstract: This paper presents an improved control strategy for both the rotor side converter (RSC) and grid side converter (GSC) of a doubly fed induction generator (DFIG)-based wind turbine (WT) system to enhance the low voltage ride through (LVRT) capability. Within the proposed control strategy, the RSC control introduces transient feed-forward compensation terms to mitigate the high frequency harmonic components and reduce the surge in the rotor currents. The proposed GSC control scheme also introduces a compensation term reflecting the instantaneous variation of the output power of the rotor side converter with consideration of the instantaneous power of grid filter impendence to keep the dc-link voltage nearly constant during the grid faults. To provide precise control, non-ideal proportional resonant (PR) controllers for both the RSC and GSC current regulation are employed to further improve dynamic performance. Simulations performed in Matlab/Simulink verify the effectiveness of the proposed control strategy.
A Novel Wind Turbine Concept Based on an Electromagnetic Coupler and the Study of Its Fault Ride-through Capability  [PDF]
Rui You,Braulio Barahona,Jianyun Chai,Nicolaos A. Cutululis
Energies , 2013, DOI: 10.3390/en6116120
Abstract: This paper presents a novel type of variable speed wind turbine with a new drive train different from the variable speed wind turbine commonly used nowadays. In this concept, a synchronous generator is directly coupled with the grid, therefore, the wind turbine transient overload capability and grid voltage support capability can be significantly improved. An electromagnetic coupling speed regulating device (EMCD) is used to connect the gearbox high speed shaft and synchronous generator rotor shaft, transmitting torque to the synchronous generator, while decoupling the gearbox side and the synchronous generator, so the synchronous generator torque oscillations during a grid fault are not transmitted to the gearbox. The EMCD is composed of an electromagnetic coupler and a one quadrant operation converter with reduced capability and low cost. A control strategy for the new wind turbine is proposed and a 2 MW wind turbine model is built to study the wind turbine fault ride-through capability. An integrated simulation environment based on the aeroelastic code HAWC2 and software Matlab/Simulink is used to study its fault ride-through capability and the impact on the structural loads during grid three phase and two phase short circuit faults.
Fault Ride through Capability Improvement of Wind Turbine Based DFIG Considering an Optimized Crowbar Along with STATCOM under Grid Fault Condition  [cached]
Alireza Zohoori,Ahad Kazemi,Rouhollah Shafaie
Research Journal of Applied Sciences, Engineering and Technology , 2013,
Abstract: Grid disturbances, especially grid faults, have very unfavorable effect on the performance of wind turbine based Doubly Fed Induction Generator (DFIG). In this study active and reactive powers control of DFIG with STATCOM has been carried out to improve Fault Ride Through (FRT) capability of a wind turbine. In order to excel improvement of the DFIG behavior under grid fault disturbances, an optimized crowbar protection method is also considered together with STATCOM. The optimized protection crowbar resistance is achieved through Analytical Hierarchy Process (AHP) algorithm. Simulations results illustrate that an optimized crowbar protection method along with STATCOM has improved the stability of wind farm and provide grid code requirement compared with that of methods without using the optimized crowbar resistance.
Remote testing on low voltage ride through of offshore wind turbines

XIE Caike
, JIANG Ziming, LIU Yutian, WANG Chunyi

- , 2017, DOI: 10.6040/j.issn.1672-3961.0.2016.218
Abstract: 摘要: 为解决长距离输电海缆对海上风电机组低电压穿越远端检测的影响问题,根据基于风力发电机出口端发展和制定的低电压穿越(LVRT)测试技术和标准,建立了低电压穿越分析模型,提出海上风电机组低电压穿越远端检测方法。按照现有检测方法分析了稳态、暂态情况下远端检测和近端检测的区别,得出远端检测中导致风机切机的外部原因为限流电抗与输电海缆的相互影响使机端电压升高、暂态过程延长、机端电压谐波含量增加。提出利用电力电子开关替代传统检测设备中的断路器,以便能精确控制电抗的动作时间。改进阻抗的动作时序,使短路电抗和限流电抗投入或退出电路的时间间隔最短,以避免限流电抗与输电海缆的相互作用对远端检测的影响。仿真验证了改进检测方法的有效性,为远端检测设备的研制提供了借鉴。
Abstract: In order to cope with the long-distance submarine cable effects on low voltage ride through(LVRT)remote testing for offshore wind turbines(WTs), the LVRT testing model was built and the method for remote testing on LVRT of offshore WTs was proposed according to the existing LVRT testing technique and standards based on the outlet of WTs. The difference between near and remote testing in both steady and transient situations was analyzed according to the existing devices and method, which concluded that the mutual influence of current limiting reactance and cable heightened the voltage of the outlet, prolonged the transient process and increased harmonic component. The circuit breaker of original device was replaced with electronic switches in order to control the operation of reactance accurately. The operation sequence of the reactance was improved to make the action intervals of time between the current-limiting reactance and short-circuit reactance trended to 0. By doing this, the mutual influence of current-limiting reactance and cable could be avoided. A simulation was put forth to verify the effectiveness of the improved process and to provide supports for development of remote LVRT testing equipment at the same time
A Novel Method on Fault Ride-Through of a DFIG Wind Turbine using a Dynamic Voltage Restorer During Symmetrical and Asymmetrical Grid Faults
S. Radha Krishna Reddy,Trishulapani. M,C. SOMASANKARAPPA,N. LAVANYA
International Journal of Engineering Innovations and Research , 2012,
Abstract: The application of a dynamic voltage restorer (DVR) connected to a wind-turbine-driven doubly fed induction generator (DFIG) is investigated. The setup allows the wind turbine system an uninterruptible fault ride-through of voltage dips. The DVR can compensate the faulty line voltage, while the DFIG wind turbine can continue its nominal operation as demanded in actual grid codes. Simulation results for a 2 MW wind turbine and measurement results on a 22 kW laboratory setup are presented, especially for asymmetrical grid faults. They show the effectiveness of the DVR in comparison to the low-voltage ride-through of the DFIG using a crowbar that does not allow continuous reactive power production.
Proportional-Resonant Control of Doubly-Fed Induction Generator Wind Turbines for Low-Voltage Ride-Through Enhancement  [PDF]
Yan Yan,Meng Wang,Zhan-Feng Song,Chang-Liang Xia
Energies , 2012, DOI: 10.3390/en5114758
Abstract: A novel control strategy is proposed in this paper for the rotor side converter (RSC) of doubly-fed induction generator (DFIG)-based wind power generation systems. It is supposed to enhance the low-voltage ride-through (LVRT) capability of DFIGs during great-level grid voltage dips. The strategy consists of a proportional-resonant (PR) controller and auxiliary PR controllers. The auxiliary controllers compensate the output voltage of the RSC in case of grid faults, thus limiting the rotor inrush current of DFIG and meeting the requirements of LVRT. Sequential-component decompositions of current are not required in the control system to improve the response of system. Since the resonant compensator is a double-side integrator, the auxiliary controllers can be simplified through coordinate transformation. The feasibility of the control strategy is validated by simulation on a 1.5 MW wind-turbine driven DFIG system. The impact of the RSC converter voltage rating on the LVRT capability of DFIG is investigated. Meanwhile, the influence of angular frequency detection and control parameters are also discussed. Compared with traditional vector control schemes based on PI current controllers, the presented control strategy effectively suppress rotor current and reduce oscillations of DFIG power and torque under grid faults.
Analysis on Low Voltage Ride Through of DFIG for Wind Power Generation

曾宬, 司大军, 王达达, 彭俊臻, 王娇
Smart Grid (SG) , 2013, DOI: 10.12677/SG.2013.35024

当系统中风电装机容量比例较大时,系统故障导致电压跌落后,风电场切除会严重影响系统运行的稳定性,这就要求风电机组具有低电压穿越(Low Voltage Ride Through, LVRT)能力,保证系统发生故障后风电机组不间断并网运行。分析了双馈风电机组的LVRT原理和基于转子撬棒保护(crowbar protection)的LVRT控制策略,在PSCAD/EMTDC中建立双馈风电机组的模型及其LVRT的控制模型,分析了有无撬棒保护对转子电流的影响,得出有撬棒保护对故障时转子电流起到衰减作用,既保护了变流器,又减少了故障电流对风电机组的冲击。
System faults may result in voltage dip due to large proportion wind power in the system. And the system stability is influenced severely when wind farms exit. So the low voltage ride through (LVRT) characteristic of wind turbines is necessary to keep wind turbine units connected to the grid after system failure. This paper analyzes the prin- ciple of LVRT in doubly fed induction generators (DFIG) and control strategy of LVRT based on rotor crowbar protec- tion, and builds the DFIG and LVRT model in the software PSCAD/EMTDC. Analyzing the inputing or not of crowbar protection on the influence of rotor current, it is concluded that crowbar protection makes the rotor current attenuation affect on fault, protection of the inverter, and reduces the fault current of the impact of wind turbines.

Fault Ride-through Capability Enhancement of VSC-HVDC-connected Offshore Wind Power Plants  [PDF]
电力系统自动化 , 2015, DOI: 10.7500/AEPS20140119001
Abstract: ToachieveactivecontroloftheACvoltagemagnitudeofwindpowerplant(WPP)collectornetworkandimprovethefaultride-through(FRT)capability,anFRTschemebasedonfeedforwardDCvoltagecontrolispresentedforvoltagesourceconverter-highvoltagedirectcurrent(VSC-HVDC)connectedoffshoreWPPs.Duringsteadystateoperation,anopenloopACvoltagecontrolisimplementedattheWPP-sideVSCoftheHVDCsystemsothatanypossiblecontrolinteractionsbetweenWPP-sideVSCandVSCofwindturbineareminimized.Whereasduringanygridfault,adynamicACvoltagereferenceismadeaccordingtoboththeDCvoltageerrorandACactivecurrentfromtheWPPcollectorsystem,thusensuringfastandrobustFRToftheVSC-HVDC-connectedoffshoreWPPs.Undertheunbalancedfaultconditioninthehostpowersystem,theresultingoscillatoryDCvoltageisdirectlyusedintheVSCACvoltagecontrollerattheWPPsidesothattheWPPcollectorsystemvoltagealsoreflectstheunbalanceinthemaingrid.TimedomainsimulationsareperformedtoverifytheefficacyoftheFRTschemebasedontheproposedfeedforwardDCvoltagecontrol.SimulationresultsshowsatisfactoryFRTresponsesoftheVSC-HVDC-connectedoffshoreWPPunderbalancedandunbalancedfaultsinthehostpowersystem,asisshownunderaseriousfaultintheWPPcollectornetwork.
Mitigation of Asymmetrical Grid Faults in Induction Generator-Based Wind Turbines Using Constant Power Load  [PDF]
Nadeem Jelani,Marta Molinas
Energies , 2013, DOI: 10.3390/en6031700
Abstract: Constant power loads (CPLs), interfaced through active rectifiers can be used for improving the stability of induction generator (IG)-based wind turbines under balanced grid voltage dips by providing the reactive power. Under asymmetrical grid faults, the negative sequence voltage produces additional generator torque oscillations and reduces the lifetime of the installed equipment. This article explores the possibility of using a CPL for mitigation of unbalanced voltage dips in an AC distribution system in addition to consuming a constant active power. Unbalanced fault mitigation as an ancillary service by the load itself could greatly increase the stability and performance of the overall power system. A CPL control structure, capable of controlling the positive and negative sequence of the grid voltage is suggested. The simulation results clearly indicate the effects of compensating the positive and negative sequence of the grid voltage on the performance of IG based wind turbines. The maximum Fault Ride Through (FRT) enhancement has been given priority and is done by the compensation of positive sequence voltage. The remaining CPL current capacity is used to compensate the negative sequence voltage in order to reduce the additional torque ripples in the IG.
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