Coordinated Rotor-Side Control Strategy for Doubly-FedWind Turbine under Symmetrical and Asymmetrical Grid Faults

In order to solve the problems of rotor overvoltage,overcurrent and DC side voltage rise caused by grid voltage drops,a coordinated control strategy based on symmetrical and asymmetrical low voltage ride through of rotor side converter of the doubly-fed generator is proposed.When the power grid voltage drops symmetrically,the generator approximate equation under steady-state conditions is no longer applicable.Considering the dynamic process of stator current excitation,according to the change of stator flux and the depth of voltage drop,the system can dynamically provide reactive power support for parallel nodes and suppress the rise of DC side voltage and rotor over-current.When the grid voltage drops asymmetrically,the positive and negative sequence components are separated in the rotating coordinate system.The doubly fed generator model is established to suppress the rotor positive sequence current and negative sequence current respectively.At the same time,the output voltage limit of the converter is discussed,and the reference value is adjusted within the allowable output voltage range.In order to adapt to the occurrence of different types of power grid faults and complex operating conditions,a fast switching module of fault type detection and rotor control mode is designed to detect the type of power grid faults and voltage drop depth in real time and switch the rotor side control mode dynamically.Finally,the simulation model of the doubly fed wind turbine is constructed in Matlab/Simulink.The simulation results verify that the proposed control strategy can improve the low-voltage ride through performance of the system when dealing with the symmetrical and asymmetric voltage drop of the power grid and identify the power grid fault type and provide the correct control strategy.

Fault Ride-Through Capability of Full-Power Converter Wind Turbine

In order to ensure power system stability, modern wind turbines are required to be able to endure deep voltage dips. The specifications that determine the voltage dip versus time are called fault r/de-through （FRT） requirements. The purpose of this paper is not only to examine the FRT behavior of a full-power converter wind turbine but also to combine the power system viewpoint to the studies. It is not enough for the turbine to be FRT capable; the loss of mains （LOM） protection of the turbine must also be set to allow the FRT. Enabling FRT, however, means that the LOM protection settings must be loosen, which may sometimes pose a safety hazard. This article introduces unique real-time simulation environment and proposes an FRT method for a wind turbine that also takes the operation of LOM protection relay into account. Simulations are carried out using the simulation environment and results show that wind turbine is able to ride-through a symmetrical power system fault.

Open-Circuit Faults Diagnosis in Direct-Drive PMSG Wind Turbine Converter

The condition monitoring and fault diagnosis have been identified as the key to achieving higher availabilities of wind turbines.Numerous studies show that the open-circuit fault is a significant contributor to the failures of wind turbine converter.However,the multiple faults combinations and the influence of wind speed changes abruptly,grid voltage sags and noise interference have brought great challenges to fault diagnosis.Accordingly,concerning the open-circuit fault of converters in direct-driven PMSG wind turbine,a diagnostic method for multiple open-circuit faults is proposed in this paper,which is divided into two tasks:The first one is the fault detection and the second one is the fault localization.The detection method is based on the relative current residuals after exponential transformation and on an adaptive threshold,and the localization method is based on the average values of fault phase currents.The scheduled diagnosis method is available to both the generator-side converter and the grid-side converter,allowing to detect and locate single and double open-circuit faults.For validating this,robustness test and multiple open-circuit faults diagnosis are presented in a 2-MW direct-driven PMSG wind turbine system,the results validate the reliability and effectiveness of the proposed method.

Floating Wind Turbine Motion Suppression Using an Active Wave Energy Converter

This paper proposes a new concept of an actively-controlled wave energy converter for suppressing the pitch and roll motions of floating offshore wind turbines.The wave energy converter consists of several floating bodies that receive the wave energy,actuators that convert the wave energy into electrical energy and generate the mechanical forces,and rigid bars that connect the floating bodies and the wind turbine platform and deliver the actuator forces to the platform.The rotational torques that are required to minimize the platform pitch and roll motions are determined using a linear quadratic regulator.The torques determined in this manner are realized through the actuator forces that maximize the wave power capture as well.The performance of the proposed wave energy converter in simultaneously suppressing the platform pitch and roll motions and extracting the wave energy is validated through simulations.

High Performance Double-Interleaved Dual Boost Converter and 3 Phase Grid Connected Converter for Wind Turbine

This paper proposes a high performance double-interleaved dual boost （DIDB） technique to solve the problems of high ripple current, large inductor size and the requirement of step-up transformer in many case found in the conventional DC-DC boost converter. The 3-phase grid connected converter with decoupling control give an independent control between active and reactive power using the load current feed-forward. With this technique, the disturbance rejection and the output power quality can be improved. Experiments are conducted with three case studies： 1） a test of the DIDB converter to determine current ripple and voltage gain, 2） a test of the 3-phase grid connected converter to determine DC-link voltage regulation, power factor and total harmonic distortion （THD）, and 3） a test of the overall system with a 7.5 kW wind turbine simulator by step and various input wind speeds to determine the output power at the grid side and verify the maximum peak power tracking （MPPT） performance. The results can confirm that the DIDB converter gives lower ripple current and higher voltage gain than the conventional converter. For the grid side, the 3-phase grid connected converter can regulate the DC-link with fast dynamic response to disturbance rejection and low overshoot while complying with the THD standard defined in IEEE 519-1992. In addition, the MPPT controller is able to achieve the maximum energy capture with the various input wind speeds.

Transient Stability Analysis of Grid-connected Converters in Wind Turbine Systems Based on Linear Lyapunov Function and Reverse-time Trajectory

As the proportion of converter-interfaced renewable energy resources in the power system is increasing,the strength of the power grid at the connection point of wind turbine generators(WTGs)is gradually weakening.Existing research has shown that when connected with the weak grid,the stability of the traditional grid-following controlled converters will deteriorate,and they are prone to unstable phenomena such as oscillation.Due to the limitations of linear analysis that cannot sufficiently capture the stability phenomena,transient stability must be investigated.So far,standalone time-domain simulations or analytical Lyapunov stability criteria have been used to investigate transient stability.However,the time-domain simulations have proven to be computationally too heavy,while analytical methods are difficult to formulate for larger systems,require many modelling assumptions,and are often conservative in estimating the stability boundary.This paper proposes and demonstrates an innovative approach to estimating the transient stability boundary via combining the linear Lyapunov function and the reverse-time trajectory technique.The proposed methodology eliminates the need of time-consuming simulations and the conservative nature of Lyapunov functions.This study brings out the clear distinction between the stability boundaries with different post-fault active current ramp rate controls.At the same time,it provides a new perspective on critical clearing time for wind turbine systems.The stability boundary is verified using time-domain simulation studies.

Dynamic modeling and direct power control of wind turbine driven DFIG under unbalanced network voltage conditions

This paper proposes an analysis and a direct power control (DPC) design of a wind turbine driven doubly-fed induction generator (DFIG) under unbalanced network voltage conditions. A DFIG model described in the positive and negative synchronous reference frames is presented. Variations of the stator output active and reactive powers are fully deduced in the presence of negative sequence supply voltage and rotor flux. An enhanced DPC scheme is proposed to eliminate stator active power oscillation during network unbalance. The proposed control scheme removes rotor current regulators and the decomposition processing of positive and negative sequence rotor currents. Simulation results using PSCAD/EMTDC are presented on a 2-MW DFIG wind power generation system to validate the feasibility of the proposed control scheme under balanced and unbalanced network conditions.

Design and Implementation of Bi-Directional DC-DC Converter for Wind Energy System

This paper proposes a design and implementation of the bi-directional DC-DC converter for Wind Energy Conversion System. The proposed project consists of boost DC/DC converter, bi-directional DC/DC converter (BDC), permanent magnet DC generator and batteries. A DC-DC boost converter is interface with proposed wind system to step up the initial generator voltage and maintain constant output voltage. The fluctuation nature of wind makes them unsuitable for standalone operation. To overcome the drawbacks an energy storage device is used in the proposed system to compensate the fluctuations and to maintain a smooth and continuous power flow in all operating modes to load. Bi-directional DC-DC converter (BDC) is capable of transforming energy between two DC buses. It can operate as a boost converter which supplies energy to the load when the wind generator output power is greater than the required load power. It also operates in buck mode which charges from DC bus when output power is less than the required load power. The proposed converter reduces the component losses and increases the performance of the overall system. The complete system is implemented in MATLAB/SIMULINK and verified with hardware.

Validation of Full-Converter Wind Power Plant Generic Model Based on Actual Fault Ride-Through Measurements

Modeling and validation of full power converter wind turbine models with field measurement data are rarely reported in papers. In this paper an aggregated generic dynamic model of the wind farm consisting of full power converter wind turbines is composed and the model validation based on actual field measurements is performed. The paper is based on the measurements obtained from the real short circuit test applied to connection point of observed wind farm. The presented approach for validating the composed model and fault ride-through （FRT） capability for the whole wind park is unique in overall practice and its significance and importance is described and analyzed.

Fuzzy Logic Controlled Dual Active Bridge Series Resonant Converter for DC Smart Grid Application

Over the last few years, smart grids have become a topic of intensive research, development and deployment across the world. This is due to the fact that, through the smart grid, stable and reliable power systems can be achieved. This paper presents a fuzzy logic control for dual active bridge series resonant converters for DC smart grid application. The DC smart grid consists of wind turbine and photovoltaic generators, controllable and DC loads, and power converters. The proposed control method has been applied to the controllable load＇s and the grid side＇s dual active bridge series resonant converters for attaining control of the power system. It has been used for management of controllable load＇s state of charge, DC feeder＇s voltage stability during the loads and power variations from wind energy and photovoltaic generation and power flow management between the grid side and the DC smart grid. The effectiveness of the proposed DC smart grid operation has been verified by simulation results obtained by using MATLAB and PLECS cards.

双馈风力发电机组变流器控制参数分步辨识方法

该文通过构建双馈风力发电机组转子侧与网侧控制系统包含8个PI控制器待辨识参数的内、外环传递函数作为参数辨识模型,基于此提出内外环施加不同扰动源的激励方法和基于改进灰狼算法的分步参数辨识方法。为避免内外环PI控制器之间的级联问题,特别选出3个合理的内外环观测量。最后,建立双馈风力发电机组仿真模型,测试所提分步辨识方法可行性,对比扰动下实际模型与辨识模型的观测量输出,证明辨识方法的准确性。

广东省周边海域风能和波浪能联合开发潜力分析

参考现有海上风电场位置选择广东省周边海域的5处联合开发场址,基于2001—2020年的风和波浪再分析数据,从资源储量和稳定性等角度对选址开展资源特征的详细分析,并评估不同额定功率的6种风力机和6种波浪能装置在选址处的发电性能。结果表明,广东省周边海域的风能和波浪能均有明显的季节分布差异,在秋冬季节更为丰富且更为稳定;风能和波浪能具有较强的相关性;风力机额定功率越大平均发电功率越大,但容量因数随额定功率的增大呈现波动趋势;风力机的容量因数明显大于波浪能装置;综合考虑多种因素,W2E-215/9.0风力机和Wave Star波浪能装置更适合投放于所提5处场址。

基于寻优算法的双馈风机变流器动态运行控制参数辨识

针对运行过程中双馈风机变流器控制参数难以获取的问题,提出了一种基于自适应混沌粒子群算法的转子侧变流器参数辨识方法。首先,基于机组实际运行下可量测电气量时间序列,建立双馈风机变流器控制系统离散化数学模型;然后,根据不同观测电气量下参数的轨迹灵敏度,对辨识难易程度进行分析;最后,利用自适应混沌粒子群算法对变流器PI控制参数进行辨识。仿真实验结果验证了所提出辨识方法的准确性与可行性。

一种基于并充串放电变换的新型直流风电机组及其控制技术

直流风电机组(DC wind turbine,DCWT)作为全直流风力发电系统的关键基础设备,其高效的拓扑结构和稳定的控制策略对于全直流风力发电系统的运行有着重要的影响。为解决目前DCWT电能变换环节过多造成的效率较低、自启动控制难度高以及故障穿越时对辅助电路依赖造成的可靠性较低等问题,提出了一种基于并充串放电变换的新型直流风电机组的拓扑结构。基于该拓扑中所采用的新型直流变换器中半桥桥臂与全桥桥臂在低压侧并联、高压侧串联的动态连接方式的特点,设计了该DCWT在不同工况下的运行控制策略;并分析了DCWT在损耗、自启动、直流故障处理等方面的运行特性。通过对比计算,验证了所提新型DCWT拓扑在通过减少电能变换环节,可有效提高能量传输效率;另通过PSCAD/EMTDC搭建了基于新型DCWT的并联型全直流发电系统仿真模型,经风电系统内DCWT在稳态、动态等正常运行工况以及故障DCWT动态切入切出、直流短路等故障运行工况下的仿真,验证了该新型DCWT在具有可行性的前提下,具备较低控制难度的自启动方式以及高可靠性的故障穿越能力。

Optimization of an annular wave energy converter in a wind-wave hybrid system

A hybrid system of a spar-type floating offshore wind turbine and a heaving annular wave energy converter(WEC)provides a promising solution for collocated ocean renewable energy exploitation.The performance of the hybrid system depends on the dimensions of the WEC.Here an optimization method is proposed to determine the outer radius and the draft of the WEC under the wave condition in a randomly chosen operational site.First,three candidate models are selected based on three operational conditions of energy harvest:(1)The natural frequency of the system is matched with the peak wave frequency in the target site(referred to as synchronized mode),where the wind turbine and the WEC nearly heave together in a near-resonance condition,(2)The natural frequency of the WEC is matched with the peak wave frequency(ring mode),(3)The maximum wave power is harnessed under the peak wave frequency(target mode).Then the candidate modes are evaluated to obtain an optimum.Results show that the extracted wave power under the above operational conditions has an upper bound that can hardly be surpassed by enlarging the dimensions of the WEC only.The optimal annual wave energy production is achieved in the synchronized mode because of the superior performance of WEC over a wide bandwidth of effective energy conversion.

Three-phase AC-DC Converter for Direct-drive PMSG-based Wind Energy Conversion System

In this paper,a wind energy conversion system(WECS)is presented for the electrification of rural areas with wind energy availability.A three-phase AC-DC converter based on a bridgeless Cuk converter is used for power extraction from the permanent magnet synchronous generator(PMSG).The bridgeless topology enables the elimination of the front-end diode bridge rectifier(DBR).Moreover,the converter has fewer components,simple control,and high efficiency,making it suitable for a small-scale WECS.A squirrel cage induction motor(SCIM)is used to emulate a MOD-2 wind turbine to implement the PMSG-based WECS.A direct-drive eight-pole PMSG is used in this study;thus,a low-input-voltage system is designed.The converter is designed to operate in the discontinuous inductor current mode(DICM)for inherent power factor correction(PFC)and the maximum power point tracking(MPPT)is achieved through the tip-speed ratio(TSR)following.The performance of the developed system is analyzed through simulation,and a 500 W hardware prototype is developed and tested in different wind speed conditions.

铝合金在风力发电机组用新型变频器冷却液中的腐蚀特性

开发了适应大型风力发电机组变频器的新型冷却液。对其进行了理化性能分析,通过失重试验、电化学测试和扫描电镜等考察了6063铝合金在新型冷却液中的耐蚀性。结果表明:新型冷却液中由于加入了对铜、铁等金属离子具有螯合作用的复合型缓蚀剂,起到了复配增效的作用,对6063铝合金具有良好的缓蚀效果。

运行参数变化时双馈风电机组振荡机理及特性研究

为研究风力机功率在风电机组中传播、变换时与风电机组各环节的耦合关系及机组输出功率振荡特性,以双馈风电机组为例,首先计及塔影效应和风剪切、风速大小,推导各子系统的能量函数;考虑机组阻尼及风速变化,分析各子系统能量变化及机组输出功率的振荡特性;最后,在PSCAD/EMTDC上建模仿真,通过能量变化深入分析风力机功率在机组内传播机理及功率振荡特性。仿真结果表明:含低频振荡分量的风力机功率通过负阻尼双馈风电机组时,与机组的次同步振荡耦合,风力机子系统、发电机及励磁子系统输出能量大幅增加,机组输出功率中既有低频振荡也有次同步振荡,它们随机组阻尼和风速变化而变化;风速变化时双馈风电机组消耗的能量主要由风力机子系统决定。

海上风电变流器故障容错低电压穿越控制

高盐雾环境下运行的海上风电变流器易发生桥臂开路故障,导致系统电压跌落时的无功电压支撑能力减弱。针对该问题,提出一种考虑变流器容错的低电压穿越模型预测控制策略。首先,基于变流器容错拓扑输出特性,阐述了变流器在容错运行下的低电压穿越机理以及分析不同工况下变流器电压矢量的可控区域,确定了变流器桥臂开路故障下低电压穿越的无功支撑需求和边界范围;其次,采用功率模型预测控制实现了在不同电压跌落程度下低电压穿越的无功支撑;最后,通过实验验证了该故障容错无功支撑机理的有效性与所提控制策略的可行性。

离网型双馈风力发电机组控制策略研究

本研究首先分析了离网型风力发电机组的数学模型,以及转子侧变换器、定子侧变换器的数学模型。然后根据数学模型,在转子侧变换器推导了直接电压矢量控制,其控制目标为定子侧的输出电压的幅值与频率;在定子侧变换器推导了基于定子电压矢量定向的矢量控制,采用电压平方外环、电流内环的双环控制,其控制目标为直流母线电压。为验证该控制策略,搭建了仿真模型,仿真结果显示,该方法能够实现离网型双馈风力发电机组输出稳定的电压。