基于确定性随机子空间方法的风机齿轮箱故障预警

齿轮箱故障是造成风电机组停机时间最长的一种故障,对其故障进行早期预警,对保证整机的可靠运行和减少维修费用具有重要意义。文章提出了一种基于确定性随机子空间方法的齿轮箱故障预测算法,首先,该算法利用齿轮箱正常状态的实时监测振动和转速数据,建立齿轮箱的状态空间模型,并得到一组参考特征值;然后利用这组参考特征值与实际监测数据所求特征值进行比较,利用均方根误差(RMSE)作为齿轮箱故障预警指标,并结合统计过程控制原理定义该指标的门槛值,来实现对齿轮箱运行状态的监控。通过对实际监测数据的仿真验证,表明了所提方法的正确性和有效性。     

基于模糊理论的水闸安全评价方法及其应用

针对水闸安全级别分类标准中既有定量指标又有定性指标,采用多指标半结构性模糊群决策理论进行分析,基于定性指标与定量指标的指标值矩阵和标准特征值矩阵具有相对统一的标准,提出基于模糊群决策理论的半结构性模糊评价方法,利用多级模糊优选模型建立了相对隶属度矩阵计算级别特征值.实例应用结果表明,该方法有效、可行,可供类似工程借鉴.     

电力负荷预测的模糊可变集合方法

应用模糊可变方法对电力负荷进行了预测.利用负荷与三大产业的生产总值的历史数据构造指标集,并应用差异函数建立电力负荷预测模型.该方法能够科学、合理地确定与电力负荷相关的各个研究指标处于级别区间的相对隶属函数,并根据指标重要性进行二元比较与量化,从而合理地确定各个指标的权重,得出电力负荷预测的级别特征值.实例证明,方法是合理的.     

输电线-防振锤体系的动力特性分析

建立了输电线振动方程,利用体系的边界条件和位移连续性准则得到一组条件方程,将防振锤对输电线的影响简化成相互作用力,由力系平衡条件构造一组平衡方程.联立两组方程并将其转换成标准特征值问题,求解得到输电线-防振锤体系频率和振型.以特高压输电线为例,计算了不同体系的频率与振型,并与理论值进行了对比.结果表明,该法为计算微风振动响应、探讨防振效果、优化防振锤的安装位置和个数奠定了基础.     

燃料电池并网发电系统控制参数协调优化方法

为提高燃料电池并网发电系统运行的小干扰稳定性,提出一种燃料电池并网发电系统控制参数全局优化方法。针对大功率质子交换膜燃料电池(PEMFC)动态特性,建立150 k W的PEMFC发电系统模型,在此基础上建立系统的小信号模型。利用特征值分析法分析确定影响系统稳定的关键参数,在充分考虑系统小干扰稳定性、阻尼比和稳定裕度协调优化情况下,利用回溯搜索算法(BSA)实现对燃料电池发电系统的关键控制参数的全局优化,仿真结果表明该方法能够有效提高大功率PEMFC并网的安全性和稳定性     

二甲醚球形扩散火焰的熄火机理研究

采用改进的PREMIX模型及"化学爆炸模式分析(CEMA)"方法,对二甲醚(DME)球形扩散火焰的熄火机理进行数值诊断,分析环境氧气摩尔分数(X_(O_2))及详细基元反应对熄火极限的影响,利用"爆炸因子"和"分岔因子"的概念,确定控制DME球形扩散火焰熄火的关键反应动力学因素。结果表明:DME冷焰具有比热焰更宽的可燃范围;冷焰对X_(O_2)的敏感性弱很多,热焰中具有正特征值的CEM首次出现在最高温度处;在熄火极限附近,CEM的特征值变为虚数,说明熄火伴随着振荡;热焰的熄火主要由小分子所参与的高温反应所控制,而冷焰熄火主要由大分子所参与的低温反应所控制。     

准PR调节下单相光伏并网逆变器的非线性研究

调节下单相LCL型光伏并网逆变器为研究对象,利用频闪映射法推导系统的离散迭代模型。通过分岔图和Matlab/Simulink仿真描述系统随电路参数变化由稳定到混沌状态的演变过程。采用雅可比矩阵法对系统的稳定性进行理论分析,得到系统在双分岔参数以及三分岔参数下的稳定工作域,并根据不同参数下的雅可比矩阵特征值确定系统的分岔类型以及失稳后的振荡频率。最后通过物理实验得到并网电流的实时波形,进一步验证了理论分析的正确性。     

基于Hopf分岔特性分析的调压室设置条件与参数判别方法

调压室是水电站输水系统缓解水击波影响,进而满足机组调节保证要求的关键建筑;调压室的设置条件、临界稳定断面和位置是工程设计阶段需科学合理确定的3个关键指标。建立考虑上游调压室和水头损失的水轮发电机组调节系统非线性模型,引入Hopf分岔理论判断系统的分岔特性;依据系统的稳定域,提出调压室的设置条件和临界稳定断面判别方法;分析调节系统水流惯性时间常数和水头损失系数对系统稳定性的影响,确定调压室的合理位置。实验结果表明,所提方法可依据系统Hopf分岔特性判别调压室设置条件、临界稳定断面位置,为工程中关于调压室设置的设计提供了理论支撑。     

电压稳定极限曲面法向量在无功补偿选址中的应用

合理地选择无功补偿装置的安装地点对于提高电力系统电压稳定性有重要意义。针对传统的失稳模式参与因子选址方法的局限性,提出了一种基于节点注入功率空间中电压稳定极限曲面的法向量指标用于无功补偿选址,并通过理论分析证明了法向量指标指导无功补偿的合理性。对IEEE39节点系统测试结果表明,与传统方法相比,法向量指标可以处理鞍结分岔和极限诱导分岔两类电压稳定临界点情况下的无功补偿选址,具有更大的适用范围。     

节能建筑外窗传热系数现场测量的简易方法

鉴于窗户传热系数现场测量复杂,本文提出一种简易方法供讨论,其关键是利用热流计测量窗户表面换热系数,利用红外热像仪测量窗户表面平均温度,并用实例说明该方法简便可行.     

基于模态法的静态电压稳定性分析

提出了基于模态法的静态电压稳定性分析的新方法,通过建立模态法的静态电压稳定分析数学模型,求取潮流方程雅可比矩阵的最小特征值及其相对应的特征向量,以最小模特征值来间接评估系统的静态电压稳定裕度,并在此基础上提出了参与因子指标,计算各个节点在最小特征值下的节点参与因子来找出哪些节点或区域的电压稳定性较差.通过对某大型电网进行研究,得到其相应的电压薄弱区域,并与灵敏度分析法所得到的结果进行对比,结果基本一致,从而验证了本文方法的合理性与有效性。     

Analysis of operating limits and combustion state regulation for low-calorific value gases in industrial burners

The effective and efficient utilization of low-calorific value (LCV) gases has gained increasing attention in scientific research and industrial fields. In this study, the combustion characteristics of three LCV gases in practical devices are analyzed by using a nonadiabatic perfectly stirred reactor model. The complete steady-state solution in the temperature-residence time parameter space is obtained with arc-length continuation. The stable operation region is quantified by the eigenvalue analysis. The transition of solution curves is quantified with heat loss coefficient. Five key system parameters are systematically investigated on their effects on stability limits. With the combustion performance being quantified by a combustion state index, a combustion state regulation method is proposed to find the optimal regulation path of system parameters. Active subspace method is further applied to shorten the regulation step by identifying the active direction. The proposed method and findings are useful for optimal regulation of burning LCV gases in industrial burners.     

基于改进的特征量描述方法的电压暂降综合评估

考虑到电压暂降本身的复杂性和用电设备的多样性,对不同站点的电压暂降严重程度进行综合评估,采用线性分段方法将暂降持续时间按其幅值进行划分,改进电压暂降特征量的描述方法,基于该方法综合考虑系统侧能量指标及用户侧严重性综合指标,其中,用户侧指标采用4种敏感设备严重程度,并结合站点监测负荷的比例合成一个统一的基于该站点负荷分布的敏感设备评价指标,最后用熵权法结合系统侧和用户侧评估指标形成新的综合评估指标。对上海市某站点实际测量数据的分析结果表明,该评估方法可客观、有效地评估站点电压暂降风险,可用于实际暂降的综合评估。     

旋转式吸附制冷系统冷量输出品质分析

冷量输出的连续性和稳定性是吸附制冷技术能否用于空调领域的关键。本文在介绍双（多）床交替吸附制冷和旋转式吸附制冷基本原理的基础上，提出了吸附制冷冷量输出品质评价指标，即冷量输出的连续性和稳定性。分析表明，双（多）床交替系统冷量输出周期长、连续性和稳定性相对较差，难以满足空调等领域的用冷要求；而旋转式系统冷量输出周期短、连续性和稳定性好，使得吸附制冷方式对空调领域的适用性大为提高。旋转式吸附制冷是一种很有发展潜力的吸附制冷方式。     

Solution of the complex eigenvalue problem for transient laminar forced convection inside tubes

Two solutions are presented for the complex eigenvalue problem arising in laminar transient forced convection inside tubes. The “method of matched asymptotic expansions” is applied to the complex eigenvalue problem yielding a closed form algebraic expression for the complex eigenvalues and two asymptotic expansions, one valid near the tube centerline and another valid near the tube wall. These expansions are combined yielding a single uniformly valid composite asymptotic expansion for the complex eigenfunctions. The present asymptotic solution is accurate for all normalized complex eigenfunctions except for those corresponding to the smaller eigenvalues. Another solution of the complex eigenvalue problem, which is accurate for the smaller eigenvalues, is presented which is based on the finite Bessel transform method. This latter solution is utilized for checking the accuracy of the closed form asymptotic solutions for the eigenvalues and the eigenfunctions of the complex eigenvalue problem.     

Thermal post-buckling of temperature dependent sandwich plates with FG-CNTRC face sheets

Present research investigates the thermal postbuckling of sandwich plates containing a stiff core and two thin carbon nanotube reinforced composite (CNTRC) face sheets. Properties of the core, carbon nanotubes (CNTs) and polymeric matrix of the faces are assumed to be temperature-dependent. It is assumed that CNTs as reinforcements may be distributed according to a functionally graded pattern. Plate is formulated based on the first-order shear deformation theory and von Kármán type of geometrical nonlinearity. The governing equations are obtained by the energy method with the aid of the Conventional Ritz method. Shape functions of the Ritz method are estimated according to the Chebyshev polynomials. A set of nonlinear eigenvalue equations is achieved. The obtained equations are homogeneous, coupled, and nonlinear in terms of both displacements and temperature. A successive displacement control strategy is implemented to trace the thermal postbuckling equilibrium path of the plate. It is shown that, with increasing the volume fraction of CNT, critical buckling temperature of sandwich plate increases and postbuckling deflection decreases. Furthermore, through a functionally graded distribution of volume fraction of CNTs across the thickness, critical buckling temperature of the sandwich plate may be enhanced and thermal postbuckling deflection may be alleviated.     

带追溯功能的窃电侦查多维离群点分析方法及应用

针对现有方法对历史月已开始的潜在持续性窃电的搜索能力较差的问题,提出一种带追溯功能的窃电侦查多维离群点分析方法。首先从集抄数据中提取出月用电量水平、日温度相关性、月温度相关性、日用电量波动率、环比增长率、谷电比重6项指标,采用多维离群点分析方法,找出当月开始窃电的疑似用户;随后,对其余用户进行历史月的多维离群点分析,找出存在历史疑似窃电起始月的用户,从最近的疑似窃电起始月至当前月,运用累计和值法对这些用户实施日用电量序列的向上水平迁移分析,将不存在向上水平迁移的情况判定为潜在的持续性窃电。对某小区的实例分析结果表明,所提方法可在不明显增加误判率的同时显著提升对窃电可疑用户的搜索率。     

GREEN'S FUNCTION APPROACH TO THREE-DIMENSIONAL HEAT CONDUCTION EQUATION OF FUNCTIONALLY GRADED MATERIALS

A Green's function approach based on the laminate theory is adopted to solve the three-dimensional heat conduction equation of functionally graded materials (FGMs) with one-directionally dependent properties. An approximate solution for each layer is substituted into the governing equation to yield an eigenvalue problem. The eigenvalues and the corresponding eigenfunctions obtained by solving an eigenvalue problem for each layer constitute the Green's function solution for analyzing the three-dimensional transient temperature. The eigenvalues and the corresponding eigenfunctions are determined from the homogeneous boundary conditions at outer sides and from the continuous conditions of temperature and heat flux at the interfaces. A three-dimensional transient temperature solution with a source is formulated by the Green's function. Numerical calculations are carried out for an FGM plate, and the numerical results are shown in tables and figures.     

Thermal postbuckling of temperature-dependent sandwich beams with carbon nanotube-reinforced face sheets

Thermal postbuckling response of a sandwich beam made of a stiff host core and carbon nanotube (CNT)-reinforced face sheets is analyzed in this research. Distribution of CNTs across the thickness of face sheets may be uniform or functionally graded. Material properties of the constituents are considered as temperature dependent. Properties of the face sheets are obtained by means of a modified rule of mixture approach. First-order shear deformation theory and von Kármán type of geometrical nonlinearity are incorporated with the virtual displacement principle. Ritz method with polynomial basis functions is applied to the virtual displacement principle to obtain the matrix representation of the governing equations. An iterative displacement control algorithm is applied to solve the nonlinear eigenvalue problem and trace the postbuckling equilibrium path. It is shown that, graded profile of CNTs, length to thickness ratio, host thickness to face thickness ratio, volume fraction of CNTs, boundary conditions, and temperature dependency, all are important factors on critical buckling temperature and postbuckling equilibrium path of sandwich beams with CNT-reinforced face sheets. However, influence of host thickness to face thickness ratio is ignorable.     

Electric Infstructure to Power a Digital Society

Several recent papers have introduced the concept of induced torque coefficients (ITCs). The concept of induced torque coefficients is essentially a generalization of the concept of damping and synchronizing torques to a multimachine, multimodal power system. This generalization allows the interactions between each stabilizing device and each machine in the system to be quantified for the purposes of a more systematic coordination of stabilizers (both PSSs and FACTS damping controllers) on a system-wide basis. In this process, a key feature is the ability to estimate, from the ITCs, the shift in system eigenvalues due to a perturbation in the gain of a stabilizer. Independently, others have developed techniques for the coordination of stabilizers based on the calculation of eigenvalue shifts from the residues. In this paper, it is shown that the eigenvalue shifts estimated by both these techniques are mathematically equivalent; the ITC approach, however, provides additional information.