变速风电系统形成强迫功率振荡扰动源分析

结合风力机运行特性,探讨永磁直驱变速风电系统成为强迫振荡源的原因。首先理论分析由风剪切和塔影效应引起的风力机机械转矩波动特性,推导出风电系统电磁转矩波动与机械转矩波动的关系表达式,采用频域法分析风电机组的输出功率特性,并通过时域仿真进行验证。研究结果表明,永磁直驱风电系统可能成为共振型低频振荡的扰动源,其功率波动频率与风力机转速相关,幅值与风力机运行点、风电系统参数和系统阻尼相关。引起共振的主要因素是塔影效应,而风剪切分量很难引发共振。     

风特性对风力发电机组输出功率的影响

为了准确研究不同类型的风速对并网风电机组输出功率的影响,建立了并网风力发电机模型和不同类型风速的模型。在不同类型风速的扰动下,对异步风电机输出功率的波动进行了仿真分析;针对引起功率振荡最严重的阵风,进行了不同频率的阵风扰动下风电机组功率振荡的比较,对阵风扰动下风电机组间的相互影响进行了仿真分析。结果表明,在相同幅值的扰动下,阵风引起的风电机组功率振荡最严重,机组功率振荡情况与阵风扰动的频率有关,单台机组在阵风扰动下产生的振荡对其他机组也会产生一定的影响。     

含频率控制的高比例风电经LCC-HVDC外送系统的机电稳定性分析

在含频率控制的风电机组经换流器高压直流输电系统（LCC-HVDC）外送的场景中,电力电子设备与同步机交互作用可能产生新的机电稳定性问题。围绕含频率控制的高比例风电经LCC-HVDC外送系统的机电时间尺度稳定性分析,建立了含高比例风电的两区四机系统经LCC-HVDC外送的全系统机电时间尺度模型,充分刻画了低频段内设备之间的耦合特性;研究了不同物理场景下风机的频率控制对直流外送系统送端电网机电振荡模式的影响,并进一步分析了直流输电频率限制控制的投入对系统机电时间尺度振荡的影响。最后,通过两区四机经LCC-HVDC外送系统时域仿真验证了理论分析的准确性。     

基于扰动观察法的模糊控制应用于光伏发电最大功率跟踪

针对扰动观察法在稳态时只能在最大功率点附近振荡运行,存在一定误差,同时结合模糊控制法在达到最大功率点后基本无波动,具有较好的动态和稳态性能特点,提出一种基于扰动观察法的模糊控制来实现最大功率跟踪,并在Boost电路上实现了其功能。仿真结果表明基于扰动观察法的模糊控制能快速、准确跟踪最大功率点,避免了最大功率点处的振荡,提高了系统稳定性和能量转换效率。     

计及受端电网调峰趋势的风-光-火特高压直流外送调度方法

考虑受端电网调峰趋势的约束,对风-光-火特高压直流外送日前调度计划进行研究,充分发掘新能源直流外送对受端电网调峰能力的补充作用。首先对风电、光伏出力特性以及风-光-火打捆联合外送优势进行分析,建立综合考虑新能源最大消纳和改善受端电网调峰裕度的调度模型。算例中运用CPLEX软件对直流外送的运行方式进行优化求解,算例结果表明,相比于传统定功率"直线式"直流外送运行方式,该文"多段折线式"运行方式能有效提高新能源使用率,降低受端电网不利调峰率和源荷扰动率,改善受端电网调峰裕度。     

基于VSG的风电机组虚拟惯量控制策略

针对永磁同步风电机组通过全功率变流器并网导致机组功率和电力系统频率解耦,机组不具备惯量响应特性的问题,综合考虑风轮、发电机、变流器特性构建"原动机-直流发电机-网侧变流器"的新型永磁同步风电系统控制模型,提出一种基于虚拟同步发电(VSG)的风电机组功率控制策略以实现机组惯量响应,提高机组电网频率支撑能力。网侧变流器基于VSG模拟传统同步发电机惯量响应特性,将系统频率变化转化为直流母线电压变化,机侧变流器利用机组风轮惯性通过发电机转矩控制实现直流母线电压的稳定。在PSCAD中基于1.5 MW永磁同步风电机组的仿真结果表明,基于VSG虚拟惯量控制策略能有效抑制电力系统频率变化,从而有效提高大规模风电场接入后系统的频率稳定性。     

DFIG-DVR系统在不平衡电网电压下的运行特性

针对双馈风电机组(DFIG)在电网电压不平衡时,二倍频扰动分量会造成定转子过电流、功率脉动、转矩脉动等一系列电气和机械的问题,提出了新型DFIG-DVR系统,即串联DVR始终维持DFIG定子端电压恒定,从根源上隔离电网不平衡故障的影响,从而在整个故障运行过程中,DFIG仍可以实现转子侧变换器功率解耦控制和网侧变换器维持直流电压恒定的目标。采用PSCAD/EMTDC建立DFIG-DVR系统模型,对比分析了电网电压不平衡时DVR的不投切与投切对DFIG的影响。结果表明,在电网电压不平衡条件下,所提控制方案可以实现DFIG的平衡运行。     

大型风电基地动态无功补偿对风电外送动态稳定性的提升作用研究

针对大型风电基地高压远距离外送存在的动态稳定性问题,采用时域与频域综合分析法研究作为风电场主要控制源之一的动态无功补偿对动态稳定性的提升与支撑作用,分析结果表明：充分利用动态无功补偿自动、快速调控无功出力的特性,响应因扰动激发出的基地外送的振荡模式,提供有效的无功支撑,进而提高阻尼特性、抑制低频振荡发生,支撑风电并网及送出。     

基于扩张状态观测器的电力系统强迫扰动监测

提出将扩张状态观测器(extended state observer,ESO)应用于电力系统强迫扰动估计问题。将电力系统的强迫扰动量扩张成新的一阶状态量,与原系统方程一起组合成新的增广系统,以此来建立扩张状态观测器,在PSCAD里搭建观测器仿真模型,通过选择合适的观测器参数,对单机无穷大系统原动机功率扰动进行仿真分析,结果表明该观测器对系统的状态和扰动量可进行准确的估计,从而验证了该方法的有效性。并在此基础上,研究了正弦波和脉冲波2种扰动形式对系统稳定性的影响,结果表明在相同幅值和频率的情况下,正弦波更易引起系统的不稳定。     

大电网发电机组电压调差系数优化和整定方法

提出了以提高系统稳定性为目标的机组调差系数优化整定理念和方法。利用该方法得到的机组调差系数,可以在提高系统同步转矩的同时不会造成阻尼转矩的恶化,有利于系统在受到扰动时保持稳定运行;仿真算例证明了该方法的有效性;编写了用于专门针对机组调差系数优化整定的软件,并在实际电网中投入使用,取得了良好的应用效果。     

Analysis on multiplicity and stability of convective heat transfer in tightly curved rectangular ducts

The present work is on bifurcation and stability of fully-developed forced convection in a tightly curved rectangular duct. Seven symmetric and four asymmetric solution branches were found. The physical mechanism and driving forces for generating various flow structures are discussed. The flow stability on various branches is determined by direct transient computation on dynamic responses of the multiple solutions. As Dean number increases, finite random disturbances lead the flows from a stable steady state to another stable steady state, a periodic oscillation, an intermittent oscillation, another periodic oscillation and a chaotic oscillation. The features of flow oscillations are examined by Hilbert spectral analysis. The mean friction factor and the mean Nusselt number are obtained for all physically-realizable flows. A significant enhancement of heat transfer can be achieved at the expense of a slight increase of flow friction.     

天然气压力能回收的热力学分析与研究趋势

目前,对于天然气长输管线在门站节流降压过程中,压力能发电等机械功利用的研究比较少,缺乏系统解决方案。文章分析了透平膨胀过程中火用降的构成,从热力学第二定律角度,对管输天然气做功能力,做了理论分析和定量计算,得出了温度火用、压力火用、化学火用的计算方法和透平膨胀输出轴功极限能力的评价因子。结合天然气压力能利用的未来要求,从机电一体化角度,提出了该领域基于总能系统理论的多学科的研究思路。     

Dynamic analysis of a grid-connected induction generator driven bya wave-energy turbine through hunting networks

The presence of forced oscillations occurring in a Wells turbine driven grid-connected induction generator enables one to seek a solution by considering the analogy between the dynamics of Wells turbine driven systems with those associated with diesel-engine driven generators or electric motors driving reciprocating compressors, where also such forced oscillations occur, although there they occur in synchronism with shaft-position or speed. This difference is taken into account and the hunting network theory, which has hitherto been applied to the dynamic analysis of motors driving reciprocating compressors, is here applied to analyse the dynamics of a Wells turbine driven grid-connected induction generator. The method enables the generator current, power and slip to be predicted from a knowledge of the shaft-torque harmonics. The result is compared with that obtained through d-q analysis     

Analysis of a possible reason for oscillation phenomena in adiesel-generator set through catastrophe theory

In this paper, a possible reason for oscillation phenomena in a diesel-generator set is investigated through digital and analog network simulations. The nonlinear simulations of a swing equation show sudden deviations in the amplitude of rotor angle oscillations, provided that there exist periodic fluctuations of mechanical inputs to the generator unit. This kind of oscillation, different from the one that is identified in linear resonance, is thought to be caused by system nonlinearities and ill-combination of system parameters. The results of the analog simulations show the occurrence of bifurcation phenomenon in a electrical power mode. An approximate nonlinear model of the swing equation is found to hold the form of Duffing's equation. From the viewpoint of Duffing's equation, an instability assessment method is proposed using a catastrophe theory analogy     

燃气轮机驱动压缩机组负荷控制参数波动问题研究

西气东输工程燃气轮机驱动压缩机组控制系统负荷控制功能不完善,造成机组在压力自动控制模式下,燃机、压缩机的转速和排气温度等重要参数在运行过程中极不稳定,并呈现周期性振动特性,对燃机重要部件造成严重的低周疲劳损伤。本文对机组的控制方式进行了研究,分析了机组功率、转速、排气温度波动的机理,通过合理调整控制器参数解决了机组关键参数波动的问题,显著改善了机组的运行稳定性和可靠性,对于提高机组的使用寿命、降低热部件的疲劳损耗具有主要作用。所做工作对机组控制系统的设计和调整具有参考价值。     

Development and assessment of a novel solar heliostat-based multigeneration system

In this paper, a comprehensive study on thermodynamic analysis and assessment, through energy and exergy approaches, is conducted for a multigenerational solar based integrated energy system. The system proposed in this study is based on heliostat solar system integrated with steam turbine. The system is also integrated with seawater reverse osmosis desalination unit and absorption cooling system. The desalination unit operates with energy recovery through the utilization of Pelton turbine. The system produces cooling, heating, fresh water and hydrogen through electrolysis. It is furthermore designed to cover the demand of 4 MW electric power with the production of 1.25 kg/h of hydrogen and 90 kg/s of fresh water. The system advisor model software is applied on a case study for the solar heliostat optimization analysis.     

基于频谱功率分配的微电网微源容量优化配置

光伏等新能源发电具有波动性,将其与可控发电装置或储能等可控微源相结合以微电网的形式发电,可减小功率波动对电网的影响。针对含光伏的独立型微电网,对其中微燃机和储能进行协调容量优化配置,通过对微电网的净负荷进行频谱分析,并考虑微燃机与储能对负荷波动的响应特性,利用优化频域分频点的方法确定微燃机与储能的功率分配策略,根据此功率分配策略,计及储能和微燃机的运维成本及储能的循环使用寿命,将分频点和电源容量作为优化变量,建立了以年综合成本最小为目标的双层优化配置模型。算例结果表明,合理的分频点可使储能与微燃机的容量配置更为经济,并可提高储能的循环使用寿命和降低微燃机的运行成本。     

A novel renewable energy-based integrated system with thermoelectric generators for a net-zero energy house

A renewable energy based integrated system is developed to meet the total energy demands of a house located off-grid, and a thermodynamic analysis through energy and exergy methodologies is conducted for analysis, evaluation, and performance assessment. The present novel multigeneration system is mainly driven through the animal residues produced at the farm house. The proposed novel system is composed of nine main units namely, a biomass combustor, photovoltaic (PV) panels, parabolic solar trough collectors, thermoelectric generators, organic Rankine cycle, electrolyzer, homogeneous charged compression ignition (HCCI) engine, absorption chiller, and reverse osmosis (RO) unit. Biomass combustor runs an organic Rankine turbine for additional power during peak loads. The exhaust of gas turbine generates cooling to meet the cooling demand of the residential area of the farm house. PV panels are incorporated to generate hydrogen through electrolyzer. A HCCI engine generates power to compensate peak load as well as charging the farming vehicles of the farm house. The RO unit with energy recovery Pelton turbine produces fresh water for farming and residential use. The advanced integration of subsystems, thermoelectric generators and efficient utilization of waste, improves significant amount of energetic and exergetic efficiencies of overall multigenerational system. The energy and exergy efficiencies are enhanced in the order of 4.8% and 6.3%, respectively, after incorporating innovative cooling system to the PV modules. The overall energy and exergy efficiencies of the proposed multigeneration system with and without thermoelectric are found to be 67.6% and 57.1%, and 68.9% and 58.4%, respectively.     

Application of simultaneous active and reactive power modulation ofsuperconducting magnetic energy storage unit to damp turbine-generatorsubsynchronous oscillations

An active and reactive power (P-Q) simultaneous control scheme, which is based on a superconducting magnetic energy storage (SMES) unit, is designed to damp out the subsynchronous resonant (SSR) oscillations of a turbine-generator unit. In order to suppress unstable torsional mode oscillations, a proportional-integral-derivative (PID) controller is used to modulate the active and reactive power input/output of the SMES unit according to speed deviation of the generator shaft. The gains of the proposed PID controller are determined by pole assignment approach based on modal control theory. Eigenvalue analysis of the studied system shows that the PID controller is quite effective over a wide range of operating conditions. Dynamic simulations using the nonlinear system model are also performed to demonstrate the damping effect of the proposed control scheme under disturbance conditions