基于超级电容储能的大容量直驱风电机组低电压穿越策略

模块化多电平换流器(modular multilevel converter, MMC)可用作大容量风电机组的换流器,其具有良好前景,但需要解决风电机组低电压故障时易脱网运行的问题。鉴于此,提出了一种基于超级电容储能的低电压穿越策略。考虑超级电容的利用效率和变流器的约束条件,通过DC-DC变换器对超级电容的储能模式进行控制,实现故障期间机、网侧的功率平衡,以稳定直流侧母线电压。按照海上风电场规定,确定了故障期间网侧MMC有功无功电流分配原则,向电网提供动态无功以帮助恢复电网电压。仿真结果表明,当并网点发生故障时,所提策略不仅能较好地稳定直流母线电压,保障了MMC功率器件安全运行,还可以补偿无功以改善电网电压,提高了大容量直驱风电机组的故障穿越能力和运行稳定性。     

提高双馈风电机组动态无功协调控制能力的实验研究

随着风电场规模不断增加,风电机组并网对电网的影响逐渐增大,故充分挖掘风电机组的无功电压调节能力和提高机组的无功响应速度对增强电力系统的电压稳定性具有重要作用。定量分析了蒙西电网某风电场单台双馈感应风力发电机(Doubly Fed Induction Generator, DFIG)的无功电压调节能力及限制因素,根据其单台机组的无功调节机理制定动态无功补偿协调控制策略。若系统无功需求超过DFIG无功出力极限时,在保证机组最大发电效益的基础上,提出基于无功差值的双馈感应风力发电机组有功附加控制。并且通过改进的遗传控制算法辨识得到附加控制器参数,该控制在降低机组最小出力的同时确保提高机组无功出力极限,进而满足系统无功需求。最后通过实验验证了所提出的双馈风电机组动态无功协调控制的可行性和准确性,增强了机组的电压稳定能力。     

含风电系统的无功优化调度

针对恒速恒频和变速恒频两类控制模式对风电机组分别进行建模,以系统有功网损最小为目标,以常规发电机和恒电压控制模型风机的无功出力、变压器抽头位置和投入的电容电抗组数为控制变量,建立了含风电系统的无功优化模型。采用原对偶内点算法进行求解,对于模型中的离散变量,提出了优化归整轮流迭代的方法来进行处理。对海南电网汛小方式的算例分析表明,该无功优化模型和方法可以明显地降低系统网损和系统运行成本。     

考虑风机排序的风电集群分层有功控制策略

随着我国风电的迅速发展,风电场有功调控趋于集群化。为合理调控风电集群有功功率、提高风电消纳量、减少风电机组调控次数,文中提出考虑风机排序控制的风电集群分层有功控制策略。根据风电场所在区域不同并结合超短期风电功率预测,将风电集群分为场群层、风电场层、机组层3个控制层。场群层和风电场层通过不同时间尺度的滚动优化提高风电消纳量;机组层通过选取影响风机调控能力的评价指标,结合熵值法与隶属度函数,计算并排序各机组调控能力评分,通过机组的排序控制减少风机调控次数。基于GAMS及Matlab平台对山西电网实际风电场数据进行分析,结果表明所提控制策略在提高风电消纳量的同时减少了风机调控次数。     

分散式风电场不同时间等级的多目标无功优化控制

针对具有一定动态无功调节能力的双馈式风力发电机组构成的分散式风电场,为解决其经济稳定运行,提出一种包含风功率预测的不同时间尺度多目标无功优化控制方法。考虑风速变化相关性分组-单机预测风电机组无功输出情况,通过风电机组和SVC共同补偿电网无功需求;根据风电预测无功功率信息,采用多目标无功控制快速有效调节其输出功率以跟踪无功补偿指令。为减少风电场内设备动作次数,选取不同时间级的控制,目标为分钟级无功控制以有功网损最小为优化目标,秒级的无功控制以电压偏差最小、电压稳定裕度最大、短时闪变最小为综合优化目标,毫秒级的无功控制以机组变流器的瞬间最大无功支撑能力为优化目标进行无功分配。工程算例证明所提策略有效的降低网损、提高电压支撑能力并保证电网正常的运行。     

Coordinated control by ADRC strategy for a wind farm based on SCIG considering low voltage ride-through capability

Wind farms are integrated with the power grid system to provide active and reactive power. Because in a wind farm, wind turbines (WTs) are highly coupled to their operating conditions, a central wind farm supervisory unit must take into account these conditions when producing power control references for each WT. The aim of this paper is to manage and control the active and reactive power of wind farms based on squirrel cage induction generators and back-to-back converters. The proportional distribution algorithm is used for distributing wind farm power to individual WTs. In addition, we consider the development of a local power management and control units for WTs. This is in order to extract the maximum available power from the wind, and to provide the active and reactive power predetermined by the transmission system operator, or to satisfy the grid code requirements considering Low Voltage Ride-through capability. The power dispatch strategy is to be used on all WTs using the distribution algorithm while ensuring the control loops using the proposed Active Disturbance Rejection Control strategy. The results demonstrate that the proposed strategies are efficient and can guarantee the safe integration of wind farms into the grid while respecting grid code requirements and power system stability.     

Towards reactive power dispatch within a wind farm using hybrid PSO

With the increasing penetration of wind power generation, the stringent grid codes are imposed by the system operators insisting the wind turbines to behave similar to that of synchronous generators. As a part of fulfilling the grid code in terms of steady state reactive power injection at point of common coupling, in this research work, the problem of optimal reactive power dispatch within a wind farm is formulated and a hybrid particle swarm optimization algorithm is proposed to get the optimal solution. The effectiveness of the proposed method is tested by simulations of the power collection grid of practical off-shore wind farm. The test results are compared with interior-point method based non-linear constrained optimization tool, fmincon, in Matlab. The analysis is carried out considering with and without wake effects on the wind farm at various grid bus voltage conditions. The test results demonstrate the effectiveness of the proposed method in achieving optimal solution for various operating conditions.     

含不同风电机组的风电电网仿真研究

为了研究包含恒速异步风力发电机和双馈异步风力发电机的风电场对电网的影响,应用Matlab 7.0建立了含不同风电机组的风电场动态模型。分析了风电场对电网暂态稳定性的影响,风电机组电压恢复情况,有功、无功变化情况,以及不同风电机组的低电压穿越能力。仿真结果表明：双馈异步风力发电机变速平稳、低电压穿越能力较强,有利于优化电能质量;当电网发生故障时,应针对不同的风电机组采取不同的控制策略以提高电力系统稳定性。     

提升无功调节能力的双馈式风力发电机转速变模式控制策略

分散式风电机组接入引起的配电网无功潮流变化易导致配电网出现电压偏差,由于配电网自身无功电压调节能力较弱,及时恢复母线电压到正常水平成为分散式风电机组的重要调节任务。提出一种以暂时牺牲最大风能追踪为代价的双馈式风电机组转速变模式控制策略。首先,以最大限度提高机组无功出力极限作为控制目标,寻求分散式风电机组向电网输送的无功功率最大值与风速、发电机转速间的关系,得到能使机组无功出力达到最大的发电机转速指令值;然后,根据控制目标及其他限制条件确定风电机组内部的无功分配方案;最后,结合传统控制算法制定双馈风力发电机转速变模式控制策略。PSCAD的仿真结果验证了所提控制策略的有效性。     

风电场功率控制策略的研究*

风速的不稳定性和间歇性使得风电机组的输出功率具有随机性和波动性。随着风电场容量的急剧增加,导致电力系统的稳定性和电能质量受到严重影响。文中搭建了双馈风力发电机组的数学模型和控制模型,采用了磁链定向矢量控制技术和电压定向矢量控制技术,针对风电机组的功率调控能力进行了深入研究与分析,提出了双馈风力发电机组的有功和无功控制策略。仿真结果表明该控制策略是合理的、可行的。     

多负荷水平下含风电接入的配电网无功优化

由于风电输出功率的随机性,风电机组的大量接入给配电网无功优化带来更多不确定性因素。为了提高配电网无功优化对风力发电并网的适应能力,建立了多负荷水平下基于场景分析的考虑风电接入的多目标无功优化模型。该模型综合考虑了节省电能损失费用和节点电压偏差2个指标,将2个指标进行模糊化,采用最大化模糊满意度指标法将多目标优化问题转换为单目标优化问题,然后采用自适应遗传算法进行求解。并以IEEE 33节点测试系统为例,计算和分析了在不同场景时最大负荷、一般负荷和最小负荷3种负荷水平下,电容器投切、系统有功损耗、节点电压以及节省电能费用情况。计算结果表明,所提出的无功模糊优化方法,在不同负荷水平、不同场景下改善电压质量和降损节能效果显著,适合多负荷水平下含风电机组的配电网无功优化需要。     

Digital control and integration of a 192 MW wind farm with doubly fed induction generator into the Brazilian power system

This paper reports on design of digital control for wind turbines and its relation to the quality of power fed into the Brazilian grid on connecting to it a 192 MW wind farm equipped with doubly fed induction generators. PWM converters are deployed as vector controlled regulated current voltage sources for their rotors, for independent control of both active and reactive power of those generators. Both speed control and active power control strategies are analyzed, in the search for maximum efficiency of conversion of wind kinetic energy into electric power and enhanced quality of delivered power.     

蓄热式电采暖负荷参与风电消纳运行策略研究

为了就地消纳大规模风力发电功率和提升电网调峰能力,将蓄热式电采暖与具有反调峰特性的风电进行结合,提出了风电与蓄热电采暖联合运行模式。模式中考虑风电机组、火电机组以及电采暖的相关约束,以系统总的发电成本最小为目标,构建了蓄热式电采暖负荷参与风电消纳优化运行模型。通过运用适应模型求解的遗传算法求解该模型,得到蓄热式电采暖负荷参与电网互动优化运行方案。仿真结果表明,基于蓄热式电采暖负荷参与风电消纳的运行策略是有效和实用的。该策略从电源侧的角度提高了系统的风能消纳水平,从电网侧的角度提升了系统的调峰能力,缓解了风电并网对系统造成的调峰压力。     

基于双模控制的永磁直驱型风力发电机组高电压穿越控制策略的研究

为提高永磁直驱型风力发电机组的高电压穿越能力,在研究电网电压骤升下风力发电机组运行特性基础上提出一种基于双模控制的永磁直驱型风力发电机组高电压穿越控制策略。以电网电压骤升幅度及直流母线电压的升高程度为依据,利用选择器进行网侧变流器控制模式的转换,从而使直驱型风力发电机组具备高电压穿越能力。基于PSCAD仿真平台的仿真结果及应用结果表明,该控制策略不仅可以保证直驱型风力发电机组在电网电压骤升期间不脱网连续运行,还可以有效提高风力发电机组的无功补偿能力,有利于电网的安全稳定运行。     

考虑拓扑影响的风电场无功优化策略研究

双馈风电机组(DFIG)机群的拓扑结构对风电场无功优化有较大影响。分析了DFIG的无功出力极限,将DFIG作为风电场连续无功源,计及风电场有载调压变压器分接头设置对DFIG机端电压的影响。以风电场内部有功损耗最小为优化目标建立风电场无功优化模型。最后,以丹麦HornsRev1离岸风电场为例,采用粒子群优化算法对所建立的无功优化模型进行求解。仿真结果验证了所提优化控制策略的安全性和经济性。     

考虑风电功率预测的分散式风电场无功控制策略

分散式风电接网模式可以解决集中式并网限电等问题,但对配电网传统运行模式带来挑战。为解决其经济稳定运行难题,提出了一种包含无功预测、无功整定、无功分配的三层新型分散式风电场无功协调控制策略。其中,无功预测层利用物理和统计方法组合预测单台机组未来无功输出能力;无功整定层针对有无无功补偿设备,提出风电机组基于电网无功缺额降出力的自身补偿和多时间尺度协调离散补偿设备、静止无功发生器(SVG)与风电机组共同补偿配电网无功需求方法;无功分配层基于风电功率预测无功功率信息,考虑风速波动性,按照优先级动态筛选风电机组,调节其输出功率以跟踪无功补偿指令。工程算例证明了所提策略可以有效提高电压支撑能力,减小风电场损耗。     

基于风电机组健康状态的风电场功率分配研究

评价风电机组健康状态,合理分配风电场中风电机组的功率,对降低风电场的运维成本有着重要意义。首先,利用风电机组监控与数据采集(supervisory control and data acquisition, SCADA)系统中的风电机组历史运行数据,训练基于长短期记忆(long short-term memory, LSTM)网络的风电机组输出功率预测模型。然后,根据预测功率和风电机组实测输出功率的偏差幅值将风电机组的健康状态分为良好、一般、较差等三个类别。最后,综合考虑风电场中每台机组的健康状态、最大发电能力和电网调度部门对风电场下达的发电指令,建立目标函数和约束条件,采用遗传算法进行求解,得到分配给每台机组的功率。仿真结果表明,所提出的方法不仅能够根据风电机组的健康状态合理分配机组功率,而且能够满足调度中心下达的风电场总的发电功率。     

Design of robust intelligent protectiontechnique for large-scale grid-connectedwind farm

This paper presents a design of robust intelligent protection technique using adaptive neuro-fuzzy inference system (ANFIS) approach to detect and classify the fault types during various faults occurrence in large-scale grid-connected wind farm. Also, it is designed to determine the fault location and isolate the wind turbine generators located in the faulted zone during fault occurrence and reconnect them after fault clearance. The studied wind farm has a total rating capacity of 120 MW, where it consists of 60 doubly fed induction generator (DFIG) wind turbines each has a capacity of 2 MW. Moreover, the wind farm generators are positioned in 6 rows, where each row consists of 10 generators. The impacts of fault type, fault location, fault duration, cascaded faults, permanent fault and external grid fault on the behaviours of the generated active and reactive power are investigated. Also, the impacts of internal and external faults in cases of different transition resistances are investigated. The simulation results indicate that, the proposed ANFIS protection technique has the ability to detect, classify and determine the fault location, then isolate the faulted zones during fault occurrence and reconnect them after fault clearance. Furthermore, the wind turbines generators which are located in un-faulted zones can stay to deliver their generated active power to the grid during fault period.     

Electrolyzer switching strategy for hydrogen generation from variable speed wind generator

This paper presents a new switching strategy for electrolyzer used in hydrogen generation which is connected to the terminal of a wind farm. The output of wind generator, in general, fluctuates greatly due to the random wind speed variations, which has a serious influence on the power system operation. In this study, the wind farm is composed of variable speed wind turbines (VSWT) driving permanent magnet synchronous generators (PMSG). The hydrogen generator (HG) is composed of rectifier and 10 electrolyzer units where each unit is controlled by the chopper circuit. To smoothen the wind farm line power, at first, a reference for the line power is generated from the difference of exponential moving average of wind farm output and its standard deviation. Then the switching strategy is developed in such a way that the proposed cooperative system can smoothen the wind farm line power fluctuation as well as generating hydrogen gas absorbing the fluctuating portion of wind farm output that lies above the reference line power. This novel switching strategy helps each electrolyzer unit working in full load and shift operation conditions and hence increases its lifespan and efficiency. The performance of the proposed system is investigated by simulation analyses, in which simulations are performed by using PSCAD/EMTDC.     

Insertion of wind generators in electrical power systems aimed at active losses reduction using sensitivity analysis

The study evaluates the electrical power system behaviour when wind turbines are inserted into the power grid. The assessment is made using a sensitivity analysis technique applied to the power flow solution. Unlike the typical algorithms, the sensitivity analysis technique does not require an iterative process, resulting in a fast method with great precision. This proposed method make easy to check the wind turbine behaviour to the changing of wind speed. Initially, the power flow solution is obtained and identified as the base case. When there are perturbations in the generators, the new solution is obtained directly by sensitivity analysis technique. The technique was applied in 34-bus, 70-bus and 126-bus test distribution system. The places chosen to connect the wind turbines were determined by the Incremental Transmission Losses method. The results demonstrate the effectiveness of the methodology. When wind turbines are inserted in the studied systems, active and reactive losses are reduced and voltage profile is improved.