基于主客观环流分型的强降水数值预报MODE检验方法及其在2019年暖季东北地区的应用

本文构建了基于主客观环流分型的强降水数值预报空间检验(MODE)方法框架,并利用该框架对欧洲中期天气预报中心全球模式(ECMWF)和中国气象局区域中尺度数值天气预报模式(CMA_MESO)的2019年暖季东北地区强降水预报进行检验。结果表明,2019年暖季东北地区54个强降水日的环流型可分为:西风槽型(15个)、副热带高压影响型(13个)、急流型(5个)、西部(12个)和东部冷涡型(9个)。其中,西风槽型和急流型以区域性强降水为主,模式对其强降水发生与否的预报能力强,TS评分较高;西部、东部冷涡型强降水的局地性强,模式对其强降水发生与否的预报能力差,TS评分低;副热带高压影响型也以区域性强降水为主,模式对其强降水发生与否的预报能力也比较强,但是对其强降水质心位置、强度、面积等属性预报偏差较大,TS评分也相对较低。另外,从两种模式预报性能对比看,CMA_MESO强降水强度和面积预报较实况普遍偏强,虽然其预报的TS评分一般高于ECMWF,但其对强降水预报的空报率也都比ECMWF大,对强降水的属性预报偏差一致性一般也低于ECMWF,其预报的可订正性整体上不及ECMWF。

含大规模新能源的电力系统STATCOM选址及容量优化

为了改善含大规模新能源电力系统电压稳定性,针对大电网系统提出了一种基于分区优化的静止同步补偿器(static synchronous compensator,STATCOM)动态无功多目标选址定容方法。提出了一种基于电气距离和暂态电压特性的分区方法,能够有效地考虑电力系统拓扑结构、线路参数以及励磁系统参数和稳定器参数等对电力系统分区的影响;采用电压控制指标辨识STATCOM最优安装节点;构建了包含投资成本、静态电压稳定指标和暂态电压严重性指标的多目标动态无功规划模型;采用基于自适应协方差矩阵和混沌搜索的多目标群搜索优化算法和熵权理想度排序法对多目标无功规划模型进行求解和决策推理。对所提方法在某省级规划电网中进行了测试,仿真结果表明,优化后的STATCOM配置方案能够有效改善电力系统静态和暂态电压稳定性。

考虑STATCOM多种控制模式的无功储备优化方法

针对静止同步补偿器(static synchronous compensator,STATCOM)在无功补偿以及抑制电压频繁波动等场景下的优良特性,对STATCOM的V-I输出特性进行详细分析,说明其参与电压控制的原理以及和容抗器相比具有的优越性。为了增大STATCOM的无功裕度,使之有足够的能力应对电力系统可能出现的各种扰动,提出STATCOM接入系统的各种控制模式,以及在稳态电压控制模式下的无功置换策略和远方自动电压控制(automatic voltage control,AVC)模式下的无功置换优化方法。在远方AVC模式下,以STATCOM无功置换后出力最小和容抗器动作次数最少为目标函数,将容抗器投切次数作为罚函数引入到目标函数中,并讨论罚函数系数的确定方法和合理性。结果表明,该无功置换优化模型可以满足调压的同时最大限度地提升STATCOM的无功裕度,同时可以使容抗器的动作次数最少。

储能型STATCOM的优化电压支撑控制策略

针对高压直流输电系统受端换流站发生接地故障时暂态电压失稳问题,提出一种综合故障检测与有功无功输出的储能型链式静止同步补偿器(static synchronous compensator,STATCOM)控制策略。储能型STATCOM具有功率四象限运行能力,通过协调装置输出的有功、无功功率可以优化电压支撑效果。首先,改进了故障检测方法,采用双重检测快速判断故障起止时刻。其次,在故障期间控制储能型STATCOM输出一定量的有功功率,可以有效抑制受端连续换相失败,抬升交流电压最低值。同时,对无功功率进行控制切换,避免故障清除后无功回撤不及时导致的受端暂态过电压问题。在PSCAD/EMTDC仿真平台的CIGRE标准系统中对所提电压支撑控制策略与储能型STATCOM常规控制进行对比。结果表明,在不同故障场景中,所提控制策略均能达到更好地电压支撑的效果。

相角前馈改善STATCOM直流电压控制的分析与仿真

STATCOM是应用非常广泛且被长期研究的灵活交流输电装置,STATCOM性能的提升和成本的降低一直是研究的重点和热点。在分析基于派克坐标变换的三相锁相环鉴相器输出特性的基础上,提出了具有相角瞬时跟踪特性的三相锁相环,改进STATCOM直流电压的暂态性能,以期通过减少直流电容容值、增加直流电压来提升直流电容或IGBT等部件的利用率。在PSCAD软件中分别搭建了三相桥STATCOM和链式级联STATCOM的等值仿真系统。系统地仿真并分析了无功电流指令的跃变,电网电压幅值、相角和频率的跃变等小扰动工况和电网发生短路故障的大扰动工况。仿真分析对比的结果表明,如STATCOM公共连接点电压相角在扰动过程中有显著变化,则新方法的直流电压控制特性显著优于传统方法,无功功率响应速度也略有提升,且能明显降低直流电容的电气应力。

Modeling of Multi-Pulse VSC Based SSSC and STATCOM

The aim of this paper is to contribute to the dynamic modeling of multi-pulse voltage sourced converter based static synchronous series compensator and static synchronous compensator. Details about the internal functioning and topology connections are given in order to understand the multi-pulse converter. Using the 24 and 48-pulse topologies switching functions models are presented. The models correctly represent commutations of semiconductor devices in multi-pulse converters, which consequently allows a precise representation of harmonic components. Additionally, time domain models that represent harmonic components are derived based on the switching functions models. Switching functions, as well as time domain models are carried out in the original abc power system coordinates. Effectiveness and precision of the models are validated against simulations performed in Matlab/Simulink?. Additionally, in order to accomplish a more realistic comparison, a laboratory prototype set up is used to assess simulated waveforms.

一种基于粗糙熵的改进K-modes聚类算法

K-modes聚类算法被广泛应用于人工智能、数据挖掘等领域。传统的K-modes聚类算法有不错的聚类效果,但是存在迭代次数多、计算量大、容易受到冗余属性的干扰等问题,且仅采用简单的0-1匹配的方法来定义2个样本属性值之间的距离,没有充分考虑每个属性对聚类结果的影响。针对上述问题,该文将粗糙熵引入K-modes算法。首先利用粗糙集属性约简算法消除冗余属性,确定各属性的重要程度;然后利用粗糙熵确定每个属性的权重,从而定义新的类内距离。将该文所提算法与传统的K-modes聚类算法分别在4组公开数据集上进行对比试验。试验结果表明,该文所提算法聚类准确率比传统的K-modes聚类算法更高。

基于电压重注式STATCOM的控制策略研究

随着电力电子器件的制造水平不断提升和人们对电能质量要求越来越高,基于电压重注式变换器的静止同步补偿器(STATCOM)动态响应速度快,不需要滤波装置且输出电压谐波含量较低,并且适用于高压大功率的输电系统。直流电压重注式STATCOM的主电路重注拓扑结构由两个三相全桥串联和附加的重注支路构成,重注支路采用级联H桥结构。重注电压产生过零区间能够实现三相全桥开关零电压通断,设计了重注支路脉冲序列构成方法并提出改进循环逻辑触发时序,仿真表明重注支路在特定的循环触发脉冲作用下可以有效抑制重注式级联H桥中电容电压不平衡。利用仿真平台验证了该变换器在过零关断、消除谐波等工作特性方面的优点。把无功电流作为直接的控制命令,建立闭环控制系统,验证该STATCOM在高压大功率系统中能够有效降低谐波含量和开关频率,提高装置和系统的运行可靠性,特别适用于高压大功率环境。

Harmonic Domain Modelling of Space Vector Based STATCOM

This paper presents frequency domain method for harmonic analysis of space vector based STATCOM. Space Vector Pulse Width Modulation (SVPWM) method is an advanced PWM method. It is a best method among all the PWM techniques. It provides a freedom in a switching cycle for placement space vector. In this paper, the SVPWM is used for switching of STATCOM. The harmonic (or frequency) domain is a steady-state form of harmonic analysis method, which represents converters to their harmonic spectra. This paper presents harmonic analysis by means of harmonic domain for space vector based Static shunt converter (STATCOM). Performance of the STATCOM is evaluated in harmonic domain simulation studies in MATLAB environment.

Effects of spot size on the operation mode of Ga As photoconductive semiconductor switch employing extrinsic photoconductivity

To guide the illuminating design to improve the on-state performances of gallium arsenide(GaAs)photoconductive semiconductor switch(PCSS),the effect of spot size on the operation mode of GaAsPCSS based on a semi-insulating wafer with a thickness of 1 mm,triggered by a 1064-nm extrinsic laser beam with the rectangular spot,has been investigated experimentally.It is found that the variation of the spot size in length and width can act on the different parts of the output waveform integrating the characteristics of the linear and nonlinear modes,and then significantly boosts the PCSS toward different operation modes.On this basis,a two-channel model containing the active and passive parts is introduced to interpret the relevant influencing mechanisms.Results indicate that the increased spot length can peak the amplitude of static domains in the active part to enhance the development of the nonlinear switching,while the extended spot width can change the distribution of photogenerated carriers on both parts to facilitate the linear switching and weaken the nonlinear switching,which have been proved by comparing the domain evolutions under different spot sizes.

UAV-assisted data collection for wireless sensor networks with dynamic working modes

Wireless Sensor Network(WSN)is a cornerstone of Internet of Things(IoT)and has rich application scenarios.In this work,we consider a heterogeneous WSN whose sensor nodes have a diversity in their Residual Energy(RE).In this work,to protect the sensor nodes with low RE,we investigate dynamic working modes for sensor nodes which are determined by their RE and an introduced energy threshold.Besides,we employ an Unmanned Aerial Vehicle(UAV)to collect the stored data from the heterogeneous WSN.We aim to jointly optimize the cluster head selection,energy threshold and sensor nodes’working mode to minimize the weighted sum of energy con-sumption from the WSN and UAV,subject to the data collection rate constraint.To this end,we propose an efficient search method to search for an optimal energy threshold,and develop a penalty-based successive convex approximation algorithm to select the cluster heads.Then we present a low-complexity iterative approach to solve the joint optimization problem and discuss the implementation procedure.Numerical results justify that our proposed approach is able to reduce the energy consumption of the sensor nodes with low RE significantly and also saves energy for the whole WSN.

Adaptive Trajectory Tracking Control for Nonholonomic Wheeled Mobile Robots:A Barrier Function Sliding Mode Approach

The trajectory tracking control performance of nonholonomic wheeled mobile robots(NWMRs)is subject to nonholonomic constraints,system uncertainties,and external disturbances.This paper proposes a barrier function-based adaptive sliding mode control(BFASMC)method to provide high-precision,fast-response performance and robustness for NWMRs.Compared with the conventional adaptive sliding mode control,the proposed control strategy can guarantee that the sliding mode variables converge to a predefined neighborhood of origin with a predefined reaching time independent of the prior knowledge of the uncertainties and disturbances bounds.Another advantage of the proposed algorithm is that the control gains can be adaptively adjusted to follow the disturbances amplitudes thanks to the barrier function.The benefit is that the overestimation of control gain can be eliminated,resulting in chattering reduction.Moreover,a modified barrier function-like control gain is employed to prevent the input saturation problem due to the physical limit of the actuator.The stability analysis and comparative experiments demonstrate that the proposed BFASMC can ensure the prespecified convergence performance of the NWMR system output variables and strong robustness against uncertainties/disturbances.

大容量STATCOM与弱受端直流VDCOL协调控制策略优化研究

由于弱交流系统电压对无功功率变化极为敏感,换流站内静止同步无功补偿器(static synchronous compensatory,STATCOM)与直流的控制若协调不当,故障后直流功率过快恢复会引起换流站的无功功率失衡、电压畸变、连续换相失败等严重问题,对直流稳定运行产生较大影响。分析了落点弱交流系统故障后直流的恢复问题,提出了一种STATCOM与直流系统的电压指令限制单元(voltage dependent current limiting,VDCOL)综合优化的方法,搭建了STATCOM与直流联合运行的RTDS仿真模型并开展仿真与现场实验验证。结果表明所提出的优化方法可限制故障后直流电流超调,减少无功功率消耗。同时直流恢复时间适当延长以及STATCOM的有效配合有利于交流电压恢复和减少后续换相失败风险,对提高弱受端交流系统中直流稳定运行的效果明显。

Real-Time 4-Mode MDM Transmission Using Commercial 400G OTN Transceivers and All-Fiber Mode Multiplexers

Weakly-coupled mode division multiplexing(MDM)technique is considered a promising candidate to enhance the capacity of an optical transmission system,in which mode multiplexers/demultiplexers(MMUX/MDEMUX)with low insertion loss and modal crosstalk are the key components.In this paper,a low-modal-crosstalk 4-mode MMUX/MDEMUX for the weakly-coupled triple-ring-core few-mode fiber(TRC-FMF)is designed and fabricated with side-polishing processing.The measurement results show that a pair of MMUX/MDEMUX and 25 km weakly-coupled TRC-FMF MDM link achieve low modal crosstalk of lower than−17.5 dB and insertion loss of lower than 11.56 dB for all the four modes.Based on the TRC-FMF and all-fiber MMUX/MDEMUX,an experiment for 25 km real-time 4-mode 3-λwavelength division multiplexing(WDM)-MDM transmission is conducted using commercial 400G optical transport network(OTN)transceivers.The experimental results prove weakly-coupled MDM techniques facilitate a smooth upgrade of the optical transmission system.

Damage constitutive model of lunar soil simulant geopolymer under impact loading

Lunar base construction is a crucial component of the lunar exploration program,and considering the dynamic characteristics of lunar soil is important for moon construction.Therefore,investigating the dynamic properties of lunar soil by establishing a constitutive relationship is critical for providing a theoretical basis for its damage evolution.In this paper,a split Hopkinson pressure bar(SHPB)device was used to perform three sets of impact tests under different pressures on a lunar soil simulant geopolymer(LSSG)with sodium silicate(Na_(2)SiO_(3))contents of 1%,3%,5%and 7%.The dynamic stressestrain curves,failure modes,and energy variation rules of LSSG under different pressures were obtained.The equation was modified based on the ZWT viscoelastic constitutive model and was combined with the damage variable.The damage element obeys the Weibull distribution and the constitutive equation that can describe the mechanical properties of LSSG under dynamic loading was obtained.The results demonstrate that the dynamic compressive strength of LSSG has a marked strain-rate strengthening effect.Na_(2)SiO_(3) has both strengthening and deterioration effects on the dynamic compressive strength of LSSG.As Na_(2)SiO_(3) grows,the dynamic compressive strength of LSSG first increases and then decreases.At a fixed air pressure,5%Na_(2)SiO_(3) had the largest dynamic compressive strength,the largest incident energy,the smallest absorbed energy,and the lightest damage.The ZWT equation was modified according to the stress response properties of LSSG and the range of the SHPB strain rate to obtain the constitutive equation of the LSSG,and the model’s correctness was confirmed.

Control method based on DRFNN sliding mode for multifunctional flexible multistate switch

To address the low accuracy and stability when applying classical control theory in distribution networks with distributed generation,a control method involving flexible multistate switches(FMSs)is proposed in this study.This approach is based on an improved double-loop recursive fuzzy neural network(DRFNN)sliding mode,which is intended to stably achieve multiterminal power interaction and adaptive arc suppression for single-phase ground faults.First,an improved DRFNN sliding mode control(SMC)method is proposed to overcome the chattering and transient overshoot inherent in the classical SMC and reduce the reliance on a precise mathematical model of the control system.To improve the robustness of the system,an adaptive parameter-adjustment strategy for the DRFNN is designed,where its dynamic mapping capabilities are leveraged to improve the transient compensation control.Additionally,a quasi-continuous second-order sliding mode controller with a calculus-driven sliding mode surface is developed to improve the current monitoring accuracy and enhance the system stability.The stability of the proposed method and the convergence of the network parameters are verified using the Lyapunov theorem.A simulation model of the three-port FMS with its control system is constructed in MATLAB/Simulink.The simulation result confirms the feasibility and effectiveness of the proposed control strategy based on a comparative analysis.

Trajectory tracking guidance of interceptor via prescribed performance integral sliding mode with neural network disturbance observer

This paper investigates interception missiles’trajectory tracking guidance problem under wind field and external disturbances in the boost phase.Indeed,the velocity control in such trajectory tracking guidance systems of missiles is challenging.As our contribution,the velocity control channel is designed to deal with the intractable velocity problem and improve tracking accuracy.The global prescribed performance function,which guarantees the tracking error within the set range and the global convergence of the tracking guidance system,is first proposed based on the traditional PPF.Then,a tracking guidance strategy is derived using the integral sliding mode control techniques to make the sliding manifold and tracking errors converge to zero and avoid singularities.Meanwhile,an improved switching control law is introduced into the designed tracking guidance algorithm to deal with the chattering problem.A back propagation neural network(BPNN)extended state observer(BPNNESO)is employed in the inner loop to identify disturbances.The obtained results indicate that the proposed tracking guidance approach achieves the trajectory tracking guidance objective without and with disturbances and outperforms the existing tracking guidance schemes with the lowest tracking errors,convergence times,and overshoots.

级联STATCOM 直流侧电容电压失衡分析

在托卡马克磁体电源系统运行过程中,发现其对应的无功补偿装置级联静止同步补偿器(STATCOM)各相链节间存在直流侧电压失衡的现象,且随着补偿电流增大。这一失衡程度有增大的趋势,这一问题会影响装置的稳定可靠运行,严重时会直接导致装置停止运行。通过建立STATCOM的电路模型,结合其电路模型建立了相应的数学模型,研究了电网谐波、电容容量、损耗以及脉冲触发延时对电容电压失衡的影响。通过MATLAB/Simulink仿真软件验证,发现电网谐波、电容容量差异、开关触发脉冲延时差异、并联型损耗差异以及混合型损耗差异是造成STATCOM直流侧电容电压失衡的重要原因。

新型SFCL与STATCOM在风电并网系统的联合应用研究

针对风电并网系统中发生三相短路故障电压跌落的问题,提出一种新型超导故障限流器(SFCL)与静止同步补偿器(STATCOM)联合应用的方法。通过搭建仿真模型,在电压稳定性改善与短路电流抑制两方面分别设置3种方案,将方案相互对比得出结论。在电压稳定性改善方面,新型SFCL与STATCOM联合控制效果最优;在短路电流抑制方面,单独利用新型SFCL控制效果最优。综合两方面考虑,利用新型SFCL与STATCOM联合控制对提高风电并网系统暂态稳定性效果最优,其不仅可以减小风电系统并网处母线电压跌落程度,还能抑制故障短路电流,维持系统暂态稳定。

Transition from a filamentary mode to a diffuse one with varying distance from needle to stream of an argon plasma jet

Plasma jet has extensive application potentials in various fields, which normally operates in a diffuse mode when helium is used as the working gas. However, when less expensive argon is used, the plasma jet often operates in a filamentary mode. Compared to the filamentary mode, the diffuse mode is more desirable for applications. Hence, many efforts have been exerted to accomplish the diffuse mode of the argon plasma jet. In this paper, a novel single-needle argon plasma jet is developed to obtain the diffuse mode. It is found that the plasma jet operates in the filamentary mode when the distance from the needle tip to the central line of the argon stream(d) is short. It transits to the diffuse mode with increasing d. For the diffuse mode, there is always one discharge pulse per voltage cycle, which initiates at the rising edge of the positive voltage. For comparison, the number of discharge pulse increases with an increase in the peak voltage for the filamentary mode. Fast photography reveals that the plasma plume in the filamentary mode results from a guided positive streamer,which propagates in the argon stream. However, the plume in the diffuse mode originates from a branched streamer, which propagates in the interfacial layer between the argon stream and the surrounding air. By optical emission spectroscopy,plasma parameters are investigated for the two discharge modes, which show a similar trend with increasing d. The diffuse mode has lower electron temperature, electron density, vibrational temperature, and gas temperature compared to the filamentary mode.