Flow separation control over an airfoil using continuous alternating current plasma actuator

The flow separation control over an NACA 0015 airfoil using continuous alternating current(AC)dielectric barrier discharge(DBD)plasma actuator is investigated experimentally and numerically.This work is intended to report some observations made from our experiment,to which little attention is paid in the previous studies,but which is thought to be important to the understanding of control of complex flow separation with AC DBD.To this end,the response of separated flow to AC plasma actuation is visualized through the time-resolved particle image velocimetry(PIV)measurement,whereas numerical simulation is carried out to complement the experiment.The flow control process at chord-based Reynolds number(Re)of 3.31×105 is investigated.It is found that the response of external flow to plasma forcing is delayed for up to tens of milliseconds and the delay time increases with angle of attack increasing.Also observed is that at the intermediate angle of attack near stall,the forced flow features a well re-organized flow pattern.However,for airfoil at high post-stall angle of attack,the already well suppressed flow field can recover to the massively separated flow state and then reattach to airfoil surface with the flow pattern fluctuating between the two states in an irregular manner.This is contrary to one’s first thought that the forced flow at any angles of attack will become well organized and regular,and reflects the complexity of flow separation control.

混合流动控制对风机叶片气动特性的影响

针对风力机叶片失速会降低风力机输出功率的问题,文章首先基于Fluent软件建立了NREL Phase Ⅵ风力机气动特性分析模型,计算风速为13 m/s时风力机叶片截面压力系数及功率特性,并与风洞实验数据进行对比,验证风力机气动特性分析模型的准确性;然后,将主动射流和涡流发生器(VGs)耦合到风力机叶片上,发现随射流孔宽度和涡流发生器高度的增加,风力机功率均呈先增后减趋势;最后,建立混合流动控制的风力机气动分析模型,研究射流与VGs弦向间距及后缘VGs高度对风力机气动特性的影响。研究表明:当间距为0.3C(C为翼型弦长)时,风力机输出功率达到最高,相比于射流单一控制,增幅为6.61%;当后缘VGs高度为15 mm时,混合式流动控制的效果最佳,风机功率最高。

双有源桥串联欠谐振变换器的最小回流电流控制

该文采用时域分析法对双有源桥串联欠谐振电路进行了分析,得到电感电流在稳态时的表达式并推导所有开关管实现软开关的条件。由于电压增益偏离1时仅采用移相控制难以实现所有开关管的软开关,因此,该文在传统移相控制的基础上,引入额外的变频控制策略,使得电路在不同的电压增益和负载条件下都能有较好的软开关性能。然而,软开关的实现会增加电路的回流电流,影响电路的传输效率。该文对所提出的变频移相控制进行了进一步的优化,使其可以在确保电路实现软开关的同时产生最小的回流电流和电感电流有效值。所提出的控制策略在一台2 kW的样机中进行了验证。

A Novel Location Method for Interline Power Flow Controllers Based on Entropy Theory

As one of the new generation flexible AC transmission systems(FACTS)devices,the interline power flow controller(IPFC)has the significant advantage of simultaneously regulating the power flow of multiple lines.Nevertheless,how to choose the appropriate location for the IPFC converters has not been discussed thoroughly.To solve this problem,this paper proposes a novel location method for IPFC using entropy theory.To clarify IPFC’s impact on system power flow,its operation mechanism and control strategies of different types of serial converters are discussed.Subsequently,to clarify the system power flow characteristic suitable for device location analysis,the entropy concept is introduced.In this process,the power flow distribution entropy index is used as an optimization index.Using this index as a foundation,the power flow transfer entropy index is also generated and proposed for the IPFC location determination study.Finally,electromechanical electromagnetic hybrid simulations based on ADPSS are implemented for validation.These are tested in a practical power grid with over 800 nodes.A modular multilevel converter(MMC)-based IPFC electromagnetic model is also established for precise verification.The results show that the proposed method can quickly and efficiently complete optimized IPFC location and support IPFC to determine an optimal adjustment in the N-1 fault cases.

基于潮流计算的变电站一键顺控功能离线测试研究

现有变电站一键顺控功能离线测试时,没有分析变电站并行效果,导致离线测试效果差,提出基于潮流计算的变电站一键顺控功能离线测试研究方法。通过一键顺控技术和其拓扑结构,构建一键顺控系统,引入潮流算法,分析变电站并行度,结合雅可比逆矩阵修正算法,完成变电站系统的并行效果分析,实现变电站一键顺控功能的离线测试。实验表明,设计方法准确获取了静态和动态功耗电流等,变电站数据量为9000个时,其值分别为131 mA和133 mA,确定了工作频率与电流值有关,因此,该方法可以实现变电站一键顺控功能离线测试,具备有效性。

基于虚拟阻抗的模块化直流电源并联均流控制研究

直流电源各模块之间的参数存在差异,导致模块化直流电源并联运行时存在环流问题。为解决该问题,研究了基于虚拟阻抗的模块化直流电源并联均流控制。文章在模块化直流电源并联运行过程中检测模块间环流,设计一种纯阻性的虚拟阻抗,并加入直流电源并联系统控制结构。通过调整虚拟阻抗来抑制并联电源模块间环流,实现模块化直流电源并联均流控制。实验结果表明,设计方法下各并联直流电源模块之间负载电流的最大偏差仅0.58 A,可以实现良好的均流控制。

双电源接入的配电网重构与优化技术研究

双电源配电环网是提高电力供应可靠性的一种常用方式。但是其潮流控制困难,电网损耗较高,因此优化潮流分布并减小配电网损耗是电力行业研究者关注的重点。柔性交流输电技术和统一潮流控制器(Unified Power Flow Controller,UPFC)的应用可以解决双电源配电环网中的潮流分布问题。将UPFC技术应用于双电源配电环网的潮流优化控制,并通过仿真试验验证方法的有效性,建立以最小化配电网有功损耗为目标的数学模型,优化在双电源配电环网中UPFC的串联补偿电压。实验结果表明,UPFC在双电源配电环网中的优化控制效果较好。

含电流型潮流控制器的柔性直流电网故障电流抑制特性分析

为有效抑制多端柔性直流电网的短路电流,提出基于限流贡献度的电流型潮流控制器(CFC)故障抑制特性量化方法,以分析CFC参数对故障电流的影响。首先,分析了由全桥开关与电容器并联组成的桥式拓扑结构CFC的工作特性,提出了在故障发生时故障限流控制模式下的控制策略,以及与直流断路器协调配合的动作时序。然后,构建含CFC限流的直流电网等效电路,推导了故障发生各阶段电流的解析表达式。在此基础上,提出CFC限流贡献度的分析方法,研究CFC不同参数和动作时序下对柔性直流故障电流的抑制特性。

透过型泥石流拦砂坝工程减灾效果分析

为了更好地理解透过型坝的减灾表现,通过对岷江上游、安宁河流域已建的透过型坝开展无人机航测、泥石流取样、室内分析测试等工作,将坝体开口形式分为横向开口、竖向开口、方形开口和混合开口4种类型,研究结果表明:区内透过型坝结构主要以方形开口为主,拦砂坝满库和半库工况占比分别为33.65%和40.38%;回淤纵坡经验值S dep=(0.31~0.83)S init,整体都表现出较好的回淤缓坡效果;在调控方面,透过型坝表现出一定的拦粗排细特征,但由于坝体开口较小,其对粒径的分选效果并不显著;透过型坝减灾中存在坝(群)开口参数设计不合理、坝体结构整体性较差、过流结构的磨蚀破坏、坝下游冲刷侵蚀和基础淘蚀破坏以及库内人工清淤不当等问题。研究成果完善了透过型坝的结构分类,加深了对其功能性的认识和理解,明确了工程实践中的问题与不足,可为工程优化设计提供技术支撑。

24kV柔性直流牵引供电系统潮流计算方法与供电特性分析

潮流分析对于研究24 kV柔性直流牵引供电系统的供电特性具有重要意义,但多层级控制导致柔性直流牵引网的潮流分布更为灵活复杂,使得原有直流牵引供电系统的潮流算法不再完全适用。为此,该文在原有直流牵引供电系统潮流计算方法的基础上,建立24 kV柔性直流牵引供电系统的“控制器-源-网-车”一体化潮流计算模型,详细分析潮流计算与控制器迭代的交互过程,提出一种连续线性潮流法和比例积分控制器(SLPFM-PI)交替迭代的潮流计算方法,以求解考虑多层级控制策略下的牵引网潮流。此外,基于潮流计算,以机车运行电压、接触网载流量为限制条件,分析24 kV柔性直流牵引变电所的供电距离,并研究了不同控制方案下系统供电特性的差异,结果表明该系统控制方案的设计中应减小机车功率的远距离、跨区间传输。

铝电解槽带电焊接过程控制专家系统

通过电热信号监测系统,采集铝电解槽各短路母线和大电流多级变阻装置的电流数据,基于毕奥-萨法尔定律,可模拟并总结出单一状态下目标施焊区域的磁场矢量,以及随大电流多级变阻装置组的电流变化规律,从而得到此状态下施焊区域最优降磁效果的控制电流组合,将所有状态关联并组合,最终形成带电焊接全过程控制专家系统。

Nyquist Stability Analysis and Capacitance Selection for DC Current Flow Controllers in Meshed Multi-terminal HVDC Grids

Controllability of DC current/power flow is essentialin multi-terminal HVDC (MTDC) grids, particularly for theMTDC grids in a meshed topology. In this paper, consideringmeshed MTDC (M2TDC) grids with the installation of twoline/multi-lineDC current flow controllers (CFCs), a small-signalmodel of the DC CFCs integrated M2TDC grids is derived,studying the impact of the power losses of the DC CFC andtheir influence on the analysis of energy exchanges. The systemstability analysis is analysed using the Nyquist diagram, which ismore suitable for analyzing complex nonlinear systems with morecompact and reliable indicators of stability in comparison withgain/phase margins shown in the Bode diagram. In addition, aselection method of the interconnected capacitor of the DC CFCis proposed under different operating conditions. The impact ofthe switching frequencies of the DC CFC on the control ranges ofthe DC current flows is analyzed. The effectiveness of the Nyquistanalysis and the capacitance selection method is verified bysimulation studies using PSCAD/EMTDC. The obtained control ranges of the DC CFC with different switching frequenciesand capacitances would be useful for practical engineeringapplications.

A DC Current Flow Controller for Meshed Modular Multilevel Converter Multiterminal HVDC Grids

This paper proposes the design of a novel DC current flow controller(CFC)and evaluates the control performance of balancing and regulating the DC branch currents using the DC CFC in a meshed multi-terminal HVDC(MTDC)grid.The DC CFC consists of two identical full bridge DC-DC converters with the capacitors of the two converters being connected in parallel.The scalability of the DC CFC is easily achievable due to the identical bridge converter topology;the cost of this DC CFC is also relatively low due to its simple physical structure and low voltage ratings.The control performance of the DC CFC is tested on a meshed 3-terminal(3-T)HVDC grid,which is based on modular multilevel converters(MMC).The DC branch current control in the meshed MTDC grid is achieved using the proposed control strategy of the DC CFC,and is verified through case studies on the real-time digital simulator(RTDS).

直流放电控制高速带斜坡锥体气动力的有效性研究

基于直流放电激波重构气动力控制原理,开展了带斜坡锥体模型的高速(Ma=6)气动力控制风洞试验,采用光纤天平技术,考察了模型在两种放电功率(284 W和517 W)下的气动力/力矩变化情况,并采用纹影成像研究了放电对流动拓扑的影响。纹影图像揭示了由于放电热阻塞和马赫数降低引起的波系重构现象,表现为放电诱导压缩波和再附激波弱化、角度减小。天平信号验证了放电使得模型的轴向力、法向力和俯仰力矩减小,放电功率较大时控制效果明显。通过求解带功率密度源项的Navier-Stokes方程模拟放电的加热效应,数值研究了模型气动力随功率密度的变化规律及加热位置对控制能力的影响。研究表明:模型气动力变化率与功率密度呈正相关;当以激励器的上游位置为参考点时,俯仰力矩变化显著;当加热位置靠近斜坡时,控制能力降低。

Analysis and Control of Modular Multi-terminal DC Power Flow Controller with Fault Current Limiting Function

In order to overcome the problems of power flow control and fault current limiting in multi-terminal high voltage direct current(MTDC)grids,this paper proposes a modular multi-terminal DC power flow controller(MM-DCPFC)with fault current limiting function.The topology structure,operation principle,and equivalent circuit of MM-DCPFC are introduced,and such a structure has the advantages of modularity and scalability.The power balance mechanism is studied and a hierarchical power balance control strategy is proposed.The results show that MM-DCPFC can achieve internal power exchange,which avoids the use of external power supply.The fault characteristics of MM-DCPFC are analyzed,fault current limiting and self-protection methods are proposed,and the factors affecting the current limiting capability are studied.The simulation models are established in PLECS,and the simulation results verify the effectiveness of MM-DCPFC in power flow control,fault current limiting,and scalability.In addition,a prototype is developed to validate the function and control method of MM-DCPFC.

Probabilistic Optimal Power Flow of an AC/DC System with a Multiport Current Flow Controller

To evaluate the impact of the randomness and correlation of photovoltaic(PV)and load on AC/DC systems with a multiport current flow controller(M-CFC),this paper proposes a probabilistic optimal power flow calculation for AC/DC systems,based on a nonparametric kernel density estimation.First,according to the M-CFC model,the DC power flow calculation method with M-CFC was inferred,and its influence on line loss was analyzed.Second,a nonparametric kernel density estimation with an adaptive bandwidth is used to accurately describe the probability distribution of the PV and load,and correlation samples of the PV and load are obtained by the mixed copula function.Then an optimization model that considers system loss and static security is established,and a fast nondominated sorting genetic algorithm based on the elite strategy(NSGA-II)is used to calculate the multi-objective probability optimal power flow of the AC/DC system.Finally,a case study is performed on a modified IEEE39 bus system using measured PV and load data.We verified that the nonparametric kernel density estimation with an adaptive bandwidth can better adapt to random component uncertainty,and M-CFC can improve the static security of the system.

具备直流潮流控制与故障限流功能的电感耦合型复合装置

高压柔性直流电网作为解决可再生能源大规模接入和消纳问题的有效手段,已成为未来电力系统的重要发展方向之一,但也使其潮流控制和故障保护的问题更加突出。为了克服以上问题、提高系统稳定性,提出了一种具备直流潮流控制与故障限流双重功能的电感耦合型复合装置。首先,提出了该复合装置的拓扑结构,该拓扑在传统直流潮流控制器基础上增加了可共用耦合电感的限流支路;其次,详细分析了直流潮流功能的工作原理、理论推导及其控制策略;然后,基于故障条件下提出的限流动作时序,进一步解析了稳态、限流、故障切除和泄能4个不同时段下耦合电感的作用效果,并研究了各时段直流故障电流的计算;最后,在MATLAB/SIMULINK仿真软件上搭建四端直流电网模型,仿真结果表明所提拓扑通过共用耦合电感实现了良好的潮流控制和抑制短路电流的功能,在短路故障状态下缩短故障电流的切除时间,在保证经济性的同时提高了系统的稳定性。

一种针对ADCP单ping流速数据的质量控制方法研究

针对TRDI公司生产的ADCP数据后处理问题,以转换至大地坐标系的.ENX格式原始数据文件为对象,提出了直接对单ping流速数据进行质量控制的处理思路。选择具有代表性的样本数据,经对比发现VTG格式的GPS地面速度信息质量优于GGA格式信息。利用VTG船速计算绝对流速,通过对比处理效果与进行显著性检验,发现箱线图法对异常值的判别效果最好。将箱线图法处理后数据按照时间间隔进行平均,并与同样本的平均数据文件比对流速的平滑性,结果表明前者的数据质量优于后者。

基于故障电流控制的新型UPFC-FCL设计

针对统一潮流控制器(UPFC)的系统短路保护问题,提出了一种基于故障电流控制的新型限流式统一潮流控制器(UPFC-FCL)拓扑结构。通过在限流电抗支路上投切耗能电阻,配合UPFC并联侧控制,限制线路故障电流的上升速率和幅值并保护设备安全。详细阐述了拓扑结构与工作原理,并进行了数学建模和关键参数设计。仿真结果表明,该新型UPFC-FCL能较精确地控制故障电流并可灵活调整限流值以配合继电保护电流整定值和断路器遮断电流,故障消除后恢复迅速且适用于多次故障和自动重合闸等情况,同时降低了装置成本以及UPFC的损坏风险。

基于节点电流注入法的UPFC潮流控制新方法研究

提出了一种基于节点电流注入法的改进的统一潮流控制器潮流控制的新方法:串联侧基于电流预测法实现对线路有功、无功功率的控制,并联侧用无功注入电流控制母线电压。利用电力系统综合程序(PSASP)的用户程序接口(UPI)功能,用C++语言编写了UPFC潮流控制模型的用户程序,与潮流程序交替求解,实现UPFC的控制功能。通过算例验证了该方法的正确性及有效性。所建模型无需改变UPFC两侧接入点的节点类型,控制灵活;基于节点电流注入法的思想对柔性交流输电系统控制器与其他商业软件的接口有借鉴意义。