A novel fast classification filtering algorithm for LiDAR point clouds based on small grid density clustering

Clustering filtering is usually a practical method for light detection and ranging(LiDAR)point clouds filtering according to their characteristic attributes.However,the amount of point cloud data is extremely large in practice,making it impossible to cluster point clouds data directly,and the filtering error is also too large.Moreover,many existing filtering algorithms have poor classification results in discontinuous terrain.This article proposes a new fast classification filtering algorithm based on density clustering,which can solve the problem of point clouds classification in discontinuous terrain.Based on the spatial density of LiDAR point clouds,also the features of the ground object point clouds and the terrain point clouds,the point clouds are clustered firstly by their elevations,and then the plane point clouds are selected.Thus the number of samples and feature dimensions of data are reduced.Using the DBSCAN clustering filtering method,the original point clouds are finally divided into noise point clouds,ground object point clouds,and terrain point clouds.The experiment uses 15 sets of data samples provided by the International Society for Photogrammetry and Remote Sensing(ISPRS),and the results of the proposed algorithm are compared with the other eight classical filtering algorithms.Quantitative and qualitative analysis shows that the proposed algorithm has good applicability in urban areas and rural areas,and is significantly better than other classic filtering algorithms in discontinuous terrain,with a total error of about 10%.The results show that the proposed method is feasible and can be used in different terrains.

Tuning method for governor control parameters of hydropower generator in isolated grid considering primary frequency performance and small-signal stability

This paper presents a method of tuning governor control parameters of an isolated hydropower generator considering the primary frequency performance and small-signal stability. First, generators that can be operated in isolated state are identified. Second, different schemes are proposed for generator mode switching from on-grid to off-grid state through comparison and mechanism analysis. Third, the time domain model and frequency domain model of the isolated generator governor are constructed to respectively estimate the primary frequency performance and small signal stability. Parameter sets that satisfy the primary frequency performance and small signal stability are acquired as optimal values of governor control parameters. Finally, the measurement-based parameters of the governor are identified and validated using simulations to demonstrate the feasibility and effectiveness of the method.

Stability Enhancement of Small-Scale Power Grid with Renewable Power Sources by Variable Speed Diesel Power Plant

This paper proposes a power control method to improve a stability of a small-scale power grid with renewable energy sources. In an isolated small- scale power grid such as an island, diesel power plant is main power source which has an environmental burden and expensive running cost due to high priced fossil fuel. Thus, expanding installation of the renewable energy sources such as a wind power is strongly desirable. Such fluctuating energy sources, however, harm power quality of the small-scale power grid, and in addition, conventional power plant in the small-scale power grid cannot, in general, stabilize the grid system with such fluctuating power sources. In this study, Variable Speed Doubly-Fed Induction Generator (VS-DFIG) is proposed to be in-stalled at a diesel power plant instead of a conventional Fixed Speed Synchronous Generator (FS-SG), because quick control of a power balance in the small-scale power grid can be achieved by using the inertial energy of VS-DFIG. In addition, utilization of a Battery Energy Storage System (BESS) is also considered to assist cooperatively the VS-DFIG control. As a result of the simulation analysis by using the proposed method, it is verified that frequency fluctuations due to renewable energy source can be effectively reduced by quick power control of the VS-DFIG compared to the conventional FS-SG, and further control ability can be obtained by utilizing BESS. Moreover, the transient stability of a small-scale power grid during a grid fault can also be enhanced.

A New Efficient Finite Volume Modeling of Small Amplitude Free Surface Flows with Unstructured Grid

A staggered finite-volume technique for non-hydrostatic, small amplitude free surface flow governed by the incompressible Navier-Stokes equations is presented there is a proper balance between accuracy and computing time. The advection and horizontal diffusion terms in the momentum equation are discretized by an integral interpolation method on the orthogonal unstructured staggered mesh and, while it has the attractive property of being conservative. The pressure-correction algorithm is employed for the non-hydrostatic pressure in order to achieve second-order temporal accuracy. A conservative scalar transport algorithm is also applied to discretize k - c equations in this model. The eddy viscosity is calculated from the k-c turbulent model. The resulting model is mass and momentum conservative. The model is verified by two examples to simulate unsteady small amplitude free surface flows where non-hydrostatic pressures have a considerable effect on the velocity field, and then applied to simulate the tidal flow in the Bohai Sea.

基于虚拟同步发电机的构网型光储变流器控制策略研究

为了抑制光伏发电的随机性和波动性的影响,提高微电网的供电可靠性,对离网工况下的微电网黑启动方案进行分析,并将其与虚拟同步发电机(Virtual Synchronous Generator,VSG)控制策略一起应用于储能变流器中,建立了储能变流器的VSG数学模型,推导了小信号模型表达式,通过在光储微电网系统引入惯性和阻尼,提高了系统电压和频率的稳定性。最后,在Matlab/Simulink仿真平台上搭建模型,验证了零起升压策略的有效性,确保了黑启动过程中线路电压的稳定;并在并网工况下分析了光储微电网系统各个微源之间的协调控制,验证了构网型光储变流器控制策略的有效性。

跟网型变换器的小扰动同步稳定机理分析与致稳控制

弱电网下,跟网型变换器易出现因阻尼不足导致的小扰动同步失稳问题。为此,该文借鉴复转矩分析理论,计及复杂控制耦合,建立跟网型变换器的复转矩模型。量化多环控制耦合、线路阻抗、控制参数等因素对系统阻尼转矩的影响,从阻尼的角度揭示跟网型变换器的小扰动同步失稳机理。根据理论分析,提出一种基于相位补偿的锁相环阻尼重塑控制策略,通过补偿多环控制耦合引入的负阻尼,增强变换器的小扰动同步稳定性。最后,开展相应的仿真与实验,验证理论分析的正确性与改进控制策略的有效性。

综合提升新能源高占比受端电网小干扰和暂态电压稳定性的SVG优化配置方法

由于新能源发电设备的弱支撑性,新能源高占比的受端电网的电压支撑强度难以满足系统安全稳定运行的要求。为了解决现有静止无功发生器(static var generator,SVG)配置方法未能充分提升系统小干扰电压稳定性和暂态电压稳定性的问题,提出了一种综合考虑系统小干扰电压稳定和暂态电压稳定的SVG优化配置方法。首先,在第一阶段考虑SVG投资运行总成本和系统小干扰电压稳定裕度,在第二阶段引入SVG接入对系统故障后暂态电压稳定裕度的影响。然后,利用基于组合赋权法和相对熵距离的改进理想解法得到最优配置方案。最后,应用PSDBPA对新能源高占比受端电网算例进行分析,验证了所提配置方法能充分发挥SVG对系统电压稳定的提升作用。

Increasing the Efficiency of Grid Tied Micro Wind Turbines in Low Wind Speed Regimes

Major problem with grid tied micro wind turbine is synchronization and wind variability. Due to this problem the stability of available grid gets reduced. The stability can be achieved by output power control of the turbine. Major part of many countries like India, the annual mean wind speed is not high. The rated wind speed of turbine remain around 11 m/s and cut in is around 3.5 m/s. Due to this problem we aimed to develop a sustainable wind energy system that can provide stable power supply even at the locations of low wind speed of 2 - 4 m/s. To address this issue, a momentary impulse or external torque to the rotor by external motor is one of the good options to maintain the momentum of blades and thus provide stability for sufficient time. Various theoretical calculations and experiments are conducted on the above method. This would increase the output power and also the efficiency of wind turbine. We show that Return-On-Investment will be high as compared with other grid connected turbines. Our proposed concept in the present study, if implemented properly, can help the installation of number of wind turbines even at domestic level. It also makes the consumers energy independent and promotes the use of wind as a source of energy and may enter as a rooftop energy supply system similar to solar.

基于TCN的跟网/构网混合型新能源场站并网系统小干扰稳定性快速评估

为支撑跟网/构网混合型新能源场站中机组控制方式快速切换,实现可适应电网强度变化的新能源场站安全稳定运行,提出基于时间卷积神经网络(temporal convolutional network,TCN)的跟网/构网混合型新能源场站并网系统小干扰稳定性快速评估方法。首先,构建跟网/构网混合型新能源场站聚合阻抗模型,通过特征值计算得到并网系统小干扰稳定裕度。然后,以并网系统短路比和新能源场站跟网/构网控制方式信息作为输入特征,以并网系统小干扰稳定裕度和阻尼比作为输出特征,训练TCN得到混合型新能源场站并网系统小干扰稳定性快速评估模型。经过训练的模型可根据短路比和跟网/构网混合型新能源场站中各机组的控制方式快速输出对应的小干扰稳定裕度和阻尼比。最后,以一个含10台风电机组的新能源场站为对象进行算例分析。结果表明:所提TCN方法相比于长短期记忆神经网络方法,在小干扰稳定裕度和阻尼比预测上的平均绝对百分比误差分别降低16.76%、14.75%;所提方法的计算耗时相对于特征值计算方法降低98.54%,从而验证所提小干扰稳定性快速评估方法的准确性与时效性。

基于虚拟母线电压控制的构网型储能变流器稳定性优化研究

构网型储能变流器作为高比例新能源接入电网的关键设备在强电网下存在稳定性问题。针对此问题,本工作提出一种基于虚拟母线电压控制的构网型储能变流器稳定性优化方法。首先,建立构网型储能变流器状态空间小信号模型,利用特征根分析法得出构网型储能变流器强电网下稳定性变差甚至振荡失稳的结论。然后,提出基于虚拟母线电压控制的稳定性优化方法,通过改变有功功率环跟踪电网电压相位的位置等效提高电网阻抗,从而提高强电网下构网型储能变流器系统并网的稳定性。接着,分析不同工况下加入虚拟母线电压控制前后系统的特征根变化趋势和稳定性提升效果,同时也分析了虚拟母线电压控制参数中补偿系数k和时间常数t对稳定性的影响并给出一般参数设计范围。最后,在MATLAB/Simulink中搭建构网型储能变流器并网模型进行时域验证,进一步搭建硬件在环实验平台进行半实物验证,验证结果表明基于虚拟母线电压控制的构网型储能变流器在强电网下的稳定性明显提高。

弱电网APF系统稳定性分析及有源阻尼方法

有源电力滤波器(APF)被广泛应用于电力系统谐波的动态补偿。然而在弱电网条件下,APF、非线性负载与电网线路阻抗间的交互容易引发补偿频率附近谐波振荡的稳定性问题,导致APF谐波补偿失效,系统的电能质量进一步恶化。通过对APF系统环路的小信号建模,揭示了弱电网APF系统的谐波振荡机理,并根据稳定性分析结论提出了一种基于电感电流反馈的有源阻尼方法抑制了这类谐波振荡,从而保证了APF在弱电网条件下稳定的谐波补偿能力。该方法的有效性经PLECS时域仿真及硬件平台实验得以验证。

考虑交直流谐波耦合的并网逆变器建模与分析

可再生能源的大规模开发利用使得逆变器在电网中的比例越来越高,逆变器与电网间谐波交互作用也愈加频繁和复杂。针对传统的建模方法无法体现逆变器与电网间谐波交互耦合的问题,文中基于谐波状态空间(HSS)理论对三相并网逆变器进行建模,该模型将交直流侧的多个频次谐波考虑在内,具有较高的精度。基于HSS模型推导出输入到输出的谐波传递函数矩阵,建立逆变器交直流谐波耦合导纳幅值图,探究交直流谐波耦合关系。然后,提出了一种适用于闭环控制系统的三相并网逆变器小信号HSS建模方法,通过计算特征值对系统稳定性进行评估以及对振荡频率进行预测。最后与MATLAB/Simulink仿真结果进行对比,验证了所建立HSS模型的准确性和系统稳定性分析的正确性。

基于广义奈奎斯特判据的新能源多场站系统小信号稳定薄弱并网单元辨识

大量新能源并网变流器接入电网极易引发小信号失稳,严重威胁系统的安全与稳定。现有的阻抗法小信号稳定性分析基于多机等效机制,仅能给出稳定性的影响因素分析,无法识别关键的稳定薄弱并网单元。该文提出一种基于广义奈奎斯特判据(generalized Nyquist criterion,GNC)的新能源多场站系统小信号稳定薄弱并网单元辨识方法。先基于GNC的稳定性分析思路,将多个不同控制参数的新能源场站解耦成多组单场站子系统;再构建每个子系统的稳定判据,分析各子系统的小信号稳定性;最后,依据子系统的小信号稳定性,找出稳定性最薄弱的子系统。研究结果表明,相较于现有方法,该方法能更准确、快速地识别小信号稳定薄弱并网单元,为系统稳定性的提升提供针对性的指导建议。

并网变流器小信号稳定性解析解

锁相环(phase-locked loop,PLL)是变流器并网同步的核心环节,现有技术通常采用基于同步坐标系的锁相环(synchronous reference frame-PLL,SRF-PLL)。由于SRF-PLL的引入,使得并网变流器模型复杂,稳定性分析困难,通常结合波特图等进行数值验证分析而难以获得解析解,更多关于稳定性的本质机理无法有效揭示。因此,提出一种基于代数运算的锁相(algebraic operation based PLL,AO-PLL)控制技术,同步速度更快,且在该锁相控制方式下,变流器模型阶次降低。基于此,给出系统稳定性的封闭解析解形式,并获得系统稳定性的充要条件,在此基础上,分析有功无功控制耦合对系统稳定性影响;揭示电流环比例控制器和积分控制器对系统稳定性的不同影响机理;解释利用短路比来刻画系统稳定裕度的内涵。此外,阐述所提AO-PLL和常规SRF-PLL之间的内在联系,以及稳定性结论在常规SRF-PLL控制下的适用性。最后通过算例验证前述理论分析的正确性。

构网型柔性直流系统阻尼环节控制策略优化研究

采用构网控制的柔性直流输电系统可模拟同步电机运行特性,为电网提供频率和电压支撑,而传统的功率同步型构网控制阻尼环节引入了调频功能,使柔直功率输出随电网频率变化而波动。该文基于同步发电机调频和阻尼环节的机理辨析,提出了功率同步型构网控制阻尼环节改进方法,可同时满足并网运行稳态功率精准控制和频率突变的阻尼需求,并基于小信号稳定分析给出了控制参数设计原则,基于电磁暂态仿真平台以及渝鄂柔性直流工程现场试验验证了改进策略的有效性。

弱联络条件下并网虚拟同步发电机小干扰稳定分析

文中研究了弱联络条件下并网虚拟同步发电机的小干扰振荡稳定性问题。首先,建立了并网虚拟同步机的简化线性化模型;然后,结合劳斯稳定判据理论,推导了并网虚拟同步机的小干扰稳定性判据。对稳定性判据的进一步分析表明:无论电网强度以及控制参数变动,并网虚拟同步机总能保持稳定运行。所以,弱联络条件不会给并网虚拟同步机带来振荡失稳问题。最后通过仿真算例,演示并验证了理论分析的正确性。

线路阻抗对构网变流器降阶模型精度影响及次同步振荡分析

在大部分关于构网变流器(GFM)次同步振荡稳定性的研究中,GFM通常被简化为只含有功率外环的三阶模型,这种降阶方法虽然简便,但其精确度会受到线路阻抗特征的影响,因此需要对GFM降阶模型适用性问题展开讨论,并提出更加精准的降阶模型。分析电网线路阻抗特征变化对降阶模型精度的影响,结果表明线路阻感比变化或短路比变化时三阶模型不能精确反映系统特性的变化,会对系统稳定性产生错误判断,其原因在于线路阻抗参数会影响电压环与功率环的耦合特性,2个控制环路均会对GFM次同步振荡稳定性产生影响。提出一种更加准确的包含电压环的降阶模型,可以精确表征线路阻抗特征变化对系统特性的影响,更加适合复杂电网下GFM的稳定性分析。基于MATLAB/Simulink仿真验证了理论分析的正确性及所提模型的有效性。

多机系统锁相环振荡模式的数值域稳定判据

针对锁相环变流器多机系统的振荡问题,提出了面向多机系统锁相环振荡模式的数值域稳定判据,完善了广义Nyquist判据的可解释性。根据实际工程运行方式,通过保留变流器导纳矩阵中主导振荡的关键元素完成模型简化,进而利用矩阵数值域代替广义Nyquist判据,将多机系统的频域导纳矩阵等效为单机系统传递函数,以其Nyquist曲线不包围点(-1,0)作为多机系统稳定的充分条件。分析结果揭示了多机系统小干扰稳定性具有不同单机外特性相互折中的现象,为实用化的电网强度分析奠定了理论基础。通过特征值分析和时域仿真说明了所提方法的有效性。

含高比例新能源和小水电的孤网频率稳定特性及涉网参数优化

含高比例小水电和新能源的地区电网被动孤网运行时,孤网内部小水电调速参数、新能源控制保护配置等直接影响孤网的稳定特性。基于实际电网孤网运行的典型案例,分析了影响孤网频率稳定的主要因素,构建了对标多类型孤网运行场景的典型仿真算例模型;通过多维度的量化仿真比对分析,提出了地区电网孤网运行时小水电机网协调、新能源涉网参数优化的一般原则。研究成果支撑孤网运行安全稳定控制预案的制定,助力新型电力系统建设和地区电网的可靠供电。

构网型变流器功率同步控制稳定性机理分析

构网型变流器具有“主动构网”能力,可以为电网提供阻尼和频率支撑,但在低阻抗电网下存在稳定性问题。为了研究低阻抗下构网型变流器功率同步控制稳定性机理,首先,建立了体现功率同步动态特性的构网型变流器接入交流电网小信号模型。然后,以功率同步控制为主体,在牛顿动力学体系框架内,建立了构网型变流器接入低阻抗电网的动力学模型,将功率的偏移量分解为同步分量和阻尼分量,用以表征功率同步控制的稳定性。接着,结合模态分析和动力学特性分析,通过研究特征根轨迹和参与因子曲线,以及阻尼分量和同步分量的变化,分析了电网强度和控制参数等对功率同步控制的影响规律,揭示其内在机理。最后,通过构网型变流器接入电网的仿真模型验证了结论的正确性。