基于β参数的光伏系统最大功率点跟踪算法研究

针对扰动观察法在最大功率点(maximum power point,MPP)附近存在振荡、跟踪步长与跟踪精度无法兼顾等问题,提出一种基于β参数的最大功率点跟踪算法,通过分析β-U曲线,在跟踪过程中分别采用变步长占空比扰动法和模糊控制法,进而提高系统跟踪速度和稳态精度。为了验证该方法的有效性,在Matlab平台对光伏系统最大功率点跟踪的稳态和动态性能进行仿真,并用"可编程直流电源"来近似模拟光伏系统进行实验研究,仿真和实验结果表明所提出的方法具有较高的稳定性能和良好的动态性能,能有效提高系统跟踪速度和控制精度,实现最大功率点跟踪。     

基于在线自调整神经网络的最大功率跟踪方法研究

针对扰动观察法易在最大功率点附近振荡的问题,研究基于在线自调整神经网络和扰动观察法结合的最大功率跟踪策略。首先提出可在线调整结构的快速资源优化网络,然后以温度、光伏阵列电压和功率为网络输入,以最大功率点电压为输出,建立MPPT神经网络模型。若当前工作状态与神经网络模型记忆模式距离较近,则以神经网络输出U_N为U_(MPP)。否则,启用扰动观察法在U_N基础上精确定位最大功率点。同时将此运行状态数据作为样本训练调整网络结构,增加记忆模式,提高网络的输出精度。仿真实验证明本方法可避免系统在最大功率点的振荡。     

ΔD法实现光伏系统最大功率点跟踪

在光伏系统中,光照强度、环境温度和负载变化等将会影响光伏系统的功率输出,因此光伏系统最大功率点跟踪(MPPT)是光伏系统研究的一个重要环节。文章在对比当前几种MPPT算法的基础上,通过改进扰动观察法得到了一种改变变换器开关频率占空比(D)来获得光伏系统最大输出功率的方案。利用MATLAB对光伏系统进行了不同工作条件下的仿真,证明其是可行的。同时,在一个实际光伏应用系统中进行占空比微增(ΔD)法最大功率点跟踪的应用试验。     

优化最大功率跟踪法在光伏水泵中的应用

通过对光伏水泵系统功率输出特点的分析,找到影响最大功率输出的影响因素,通过进一步对光伏输出I-V曲线和P-U曲线分析,提出了一种对最大功率点跟踪(MPPT)扰动观察法的优化算法和实现方法,解决了MPPT扰动观察法在最大功率点附近震荡的问题。     

基于改进人工鱼群算法的光伏系统MPPT研究

针对光伏系统最大功率点跟踪(MPPT)传统算法的不足,提出一种改进的人工鱼群算法(IAFSA),该算法将扰动观察法(PO)引入到人工鱼群算法。首先利用扰动观察法实时性强和跟踪快速的特点找到系统的最大功率点,然后由人工鱼群算法对全局最大功率点进行快速搜索跟踪,确定功率点极值,避免了扰动观察法使功率最大点陷入局部极值的问题。应用Matlab仿真,分别以标准环境温度下光照均匀和光照部分被遮蔽以及不同环境温度下光照部分被遮蔽3种条件对IAFSA与传统的PO和PSO算法最大功率点跟踪效果进行比较,仿真结果表明,采用IAFSA算法可有效跟踪光伏系统的最大功率点,提高系统的应用效率。     

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。     

基于中值步长法的光伏阵列最大功率点跟踪

提出了光伏阵列最大功率点跟踪的新型变步长扰动观察法,即中值步长法。在外界环境发生变化时,利用斜率判断扰动方向,利用启动步长快速跟踪光伏阵列最大功率点的大概位置;然后每扰动一次就将扰动步长取中值,使系统在稳态时最大限度地逼近最大功率点,减小最大功率点附近的震荡,提高跟踪精度;利用功率判断避免在扰动过程中出现算法错误。通过Matlab进行仿真,证明了中值步长法能达到理想的跟踪效果。     

基于模糊控制的太阳电池最大功率点跟踪算法研究

通过分析太阳电池的输出特性及最大功率点跟踪(MPPT)的基本原理,在电导增量法的基础上,采用模糊控制确定跟踪步长的大小和方向。在Matlab仿真环境下,建立模糊控制器和降压式(Buck)变换电路,在标准测试条件、光照强度和温度变化的情况下分别使用模糊控制法、扰动观察法和电导增量法进行最大功率点跟踪,仿真结果表明模糊控制法比扰动观察法和电导增量法在寻找最大功率点的速度和跟踪过程的稳定性上都要优越。     

光伏系统的一种VWP区间模糊MPPT控制策略

在优化光伏系统最大功率跟踪(maximum power point tracking,MPPT)快速性、准确性和平稳性的同时,为简化模糊控制器的设计,提出一种可变天气参数(variable weather parameters,VWP)区间模糊MPPT控制策略。该策略以理想最大功率点(maximum power point,MPP)所对应的控制量为中心建立一个VWP区间并将MPP的寻优范围限制在该区间内,可明显提高跟踪的快速性,同时通过减小模糊控制器的寻优步长保证搜索的准确性和平稳性。最后,仿真实验显示该控制策略的良好运行性能,验证该控制策略有比扰动观察法更好的MPPT暂态性能。     

基于神经网络的改进扰动观察法MPPT控制

为进一步提高光伏发电系统的输出效率和动态调节性能,设计基于神经网络的改进扰动观察法最大功率点跟踪(MPPT)控制.该方法在扰动观察法基础上引入神经网络算法,使得在环境剧烈变化时,系统动态调节速度加快.通过系统仿真和硬件实测,得出该改进扰动观察法相比于传统扰动观察法和神经网络法,在一定程度上能加快动态调节速度和减小稳态误...     

A novel maximum power point tracker for thermoelectric generation system

In this paper, a novel hybrid maximum power point tracking (MPPT) method is proposed and investigated. The proposed MPPT technique combines the simplicity of perturb and observe (P&O) method and the fast tracking ability of open circuit voltage (OCV) method. The advantages of the proposed MPPT approach include fast tracking speed, no additional circuit required and no temporary power loss. To validate the feasibility of the proposed MPPT technique, an 1.2 kW thermoelectric generation system for industrial waste heat recovery is also constructed, experimental results show that comparing with conventional P&O technique, the proposed method can improve the tracking speed for 42.9% and 86.2% when temperature differences are ΔT = 60 °C and ΔT = 180 °C, respectively. Moreover, the energy loss can be improved by 24.0% and 87.0% when temperature differences are ΔT = 60 °C and ΔT = 180 °C, respectively.     

A Comparative Study of Flux Limiters Using New Numerical Methods in Unsteady Supersonic Flows

In this study, partition of the energy equation in the Euler equations is expanded in the form of ideal mixture gas through the finite-volume method in order to discuss questions faced in the Riemann approximation solver. Through the AUSMDV numerical flux scheme with different flux limiters and types of gradient, we want to improve the calculation accuracy and reduce the nonphysical oscillation problem. Based on the AUSMDV scheme, We modify the energy equation of the ideal mixture gas which was proposed by Ton [8 V. T. Ton , Improved Shock-Capturing Methods for Multicomponent and Reacting Flows , J. Comput. Phys. , vol. 128 , pp. 237 – 235 , 1996 .[Crossref], [Web of Science ®] , [Google Scholar]]. For the pressure and velocity gradient of source term Q, we establish a new method of gradient control to test whether it can make progress in the nonphysical numerical oscillation problem.     

光伏电池最大功率点跟踪方法的研究

在光伏发电系统中,为了提高光伏电池的利用效率,需要对光伏电池的最大功率点进行跟踪。分析了在跟踪控制中常见的扰动跟踪法和功率数学模型法,比较了它们的优缺点,并基于这两种方法提出了一种改进的跟踪方法,利用MATLAB对该方法进行了仿真研究,仿真结果验证了该方法的有效性。     

An enthalpy-based lattice Boltzmann formulation for unsteady convection-diffusion heat transfer problems in heterogeneous media

In this paper, we propose a direct extension of a previous work presented by Hamila et al. [1 R. Hamila, M. Nouri, S. Ben Nasrallah, and P. Perré, Int. J. Heat Mass Transfer, vol. 100, pp. 728–736, 2016.[Crossref], [Web of Science ®] , [Google Scholar]] dealing with the simulation of conjugate heat transfer by conduction in heterogeneous media. In [1 R. Hamila, M. Nouri, S. Ben Nasrallah, and P. Perré, Int. J. Heat Mass Transfer, vol. 100, pp. 728–736, 2016.[Crossref], [Web of Science ®] , [Google Scholar]] a novel enthalpy-based lattice Boltzmann (LB) formulation was successfully simulated in several conjugate heat transfer problems by conduction. We propose testing this enthalpic LB formulation in solving convection-diffusion heat transfer problems in heterogeneous media. The main idea of this formulation is to introduce an extra source term, avoiding any additional treatment of the distribution functions at the interface. Continuity of temperature and normal heat flux at the interface is satisfied automatically. The performance of the present method is successfully validated by comparison to the control volume methods (CVMs) solutions of several heat convection-diffusion problems in heterogeneous media.     

输电线路导线及地线复用新型直流融冰装置技术研究综述

  [目的]  在雨雪冰冻气候环境下,为了避免输电线路冰雪灾害事故的发生,需对输电线路进行融冰以加强其抵御冰雪灾害的能力,直流融冰装置是一种近年来应用广泛且行之有效的融冰装置。  [方法]  通过建立一种可行且有意义的技术来解决采用完全独立的两套融冰设备直流融冰装置设备投资大,占地面积增大,运维等费用成倍增加,整体经济性差的问题。提出一种可行的方法,即介绍了一种导线及地线复用新型直流直流融冰装置的主电路拓扑结构,可以一套装置实现导线和地线复用直流融冰的功能。  [结果]  获得的结果证明了这种技术是可行的和有效的。  [结论]  这项技术为进一步研究解决输电线路导线和地线覆冰、降低直流融冰装置投资、提高输电系统抵御自然灾害的能力具有重要参考意义。     

分布式供能系统建模优化能流逻辑思维图详解

针对复杂分布式供能系统DES/CCHP建模优化中把不同子系统的目标函数形式上加合成为系统目标函数但因其相互间并不存在关联而无法求解的问题，给出了表述DES/CCHP与其各个子系统的能流关系的逻辑思维图，指出了DES/CCHP包括蒸汽动力、区域供冷、区域供暖、生活热水、可再生能源发电、工业余热利用、智能微电网、天然气微网及LNG物流、氢能等9个子系统，提出了采用分解协调优化的策略和方法；首先对拓扑结构、设备参数、各种变量之间有可描述关系的各子系统分别建模和优化求解；然后在各个子系统之间多次迭代协调优化，电力是最主要的协调变量；进而指出上图是物理模型和能流模型的集成，但也蕴含着多种功能层次模型；只有在多种运行/营销层次工况初步优化结果的基础上才能建立设计/决策层次模型，并反复迭代才能获得优化结果。强调优化的直接目标是经济性，最高能效目标来自基于科学用能原理所选择的子系统拓扑结构和参数，碳排放最少的目标则取决于能效和一次能源的构成。上述方法已用于多个天然气DES/CCHP工程的规划和建设，有重要的科学意义和实用前景。     

A New Solution of One Birkhoff Problem

In 1926, G. D. Birkhoff in [1] has formulated the following problem: describe the set of all ordinal numbers for which there exist dynamical systems with center depths (the definition will be given later) equal to them. In this case, Birkhoff used the term ordinal numbers of central trajectories instead of center depths however, the both terms mean the same. In 1948, A. G. Maier gave an answer to this question. In [2], he presented a construction of a flow having an arbitrary (given) center depth the phase space of which is a subset of . The present paper gives a new solution of Birkhoff's problem based on some methods of symbolic dynamics. The mentioned methods were earlier used by the author ([3], [4]) in his study of one topological invariant of symbolic dynamical systems, which obtained the name of depth. (To avoid any misunderstanding, we emphasize that terms depth and center depth stand for different concepts though sound likely; the depth of the center of some dynamical system and its center depth need not to be the same ordinal numbers.) A new construction of dynamical systems with arbitrary center depth, which is presented below, seems to be more simple and clear than Maier's construction.     

V2O5-WO3/TiO2催化剂的制备及其动力学分析

采用浸渍法制备了V2O5-WO3/TiO2催化剂,考察了各运行工况对催化剂脱硝活性的影响,在实验的基础上,建立了经验性催化反应动力学方程。结果表明：当催化剂粒径小于40目、空速小于30000h-1时,可以消除SCR脱硝反应的内外扩散的影响。V2O5-WO3/TiO2催化剂的催化还原反应是一级催化反应,反应活化能为能为24232 J/mol,在消除内外扩散影响和NH3/NO比大于1的情况下,NO的反应级数为1.0493,O2的反应级数为1.1366,从而可以得到V2O5-WO3/TiO2催化剂催化反应速率方程式。     

Determination of thermal conductivity and emissivity of electromagnetically levitated high-temperature droplet based on the periodic laser-heating method: Theory

Recently, a novel method of measuring the thermophysical properties, especially thermal conductivity, of high-temperature molten materials using the electromagnetic levitation technique has been developed by [H. Fukuyama, H. Kobatake, I. Minato, K. Takahashi, T. Tsukada, S. Awaji, Establishment of noncontact AC calorimetry of high-temperature melts using solid platinum spheres as a reference, in: Proceedings of 16th Symposium on Thermophysical Properties, CD-ROM, 2006, p. 937; H. Kobatake, H. Fukuyama, I. Minato, T. Tsukada, S. Awaji, Noncontact AC calorimetry of liquid silicon with suppressing convections in a static magnetic field, in: Proceedings of 16th Symposium on Thermophysical Properties, CD-ROM, 2006, p. 625], where the method was based on periodic laser-heating, and a static magnetic field was superimposed to suppress convection in an electromagnetically levitated droplet. In the present work, the periodic laser-heating method was modeled to estimate the thermal conductivity and emissivity of the electromagnetically levitated droplet using a measured parameter, i.e., the phase lag between the modulated light and the temperature variations detected by a pyrometer, Δϕ_s, at various frequencies of the modulated light ω. Here, the unsteady-state heat conduction equation for the droplet accompanying radiative heat transfer to the ambient was simplified and transformed to steady-state linear equations. The experimental relation between Δϕ_s and ω was fitted by the mathematical model proposed here to estimate simultaneously the thermal conductivity and emissivity of molten silicon. Also, the numerical simulations for unsteady thermal field in the electromagnetically levitated droplet which was periodically laser-heated were carried out to demonstrate the validity of the proposed simplified model, and then to investigate the sensitivity of the thermophysical properties to the relation between Δϕ_s and ω.