基于半不变量随机潮流计算的分布式光伏优化配置研究

针对新能源大规模并网引发电压质量下降及网络损耗增加等问题,提出了一种基于半不变量随机潮流计算的分布式光伏选址定容的新方法。首先,将接入IEEE33节点配电网的光伏出力及配电网自身的负荷进行随机性建模,以此模拟真实情况下的配电网光伏出力与负荷变化。其次,以运行成本和网损为目标函数建立选址定容优化模型,采用半不变量潮流计算得到各个节点电压和各支路功率的半不变量,利用改进粒子群算法寻优得出分布式光伏的最优接入节点及对应容量。最后,通过IEEE33节点配电网仿真分析,验证了所提方法有效性。     

Impacts of distributed photovoltaics on network voltages: Stochastic simulations of three Swedish low-voltage distribution grids

The continuously increasing application of distributed photovoltaics (PV-DG) in residential areas around the world calls for detailed assessment of distribution grid impacts. Both photovoltaic generation and domestic electricity demand exhibit characteristic variations on short and long time scales and are to a large extent negatively correlated, especially at high latitudes. This paper presents a stochastic methodology for simulation of PV-DG impacts on low-voltage (LV) distribution grids, using detailed generation and demand models. The methodology is applied to case studies of power flow in three existing Swedish LV grids to determine load matching, voltage levels and network losses at different PV-DG penetration levels. All studied LV grids can handle significant amounts of PV-DG, up to the highest studied level of 5 kW_p PV per household. However, the benefits of PV-DG in terms of relative improvement of on-site reduction of demand, mitigated voltage drops and reduced losses were most significant at a penetration level of 1 kW_p PV per household.     

考虑电动汽车充电负荷的配电系统场景概率潮流分析

提出了一种同时考虑分布式光伏出力和电动汽车充电负荷随机特性的配电系统场景概率潮流分析方法。首先,在考虑车主交通行为与充电模式随机特性的基础上,采用蒙特卡洛模法对充电站典型日内的充电负荷进行模拟,给出充电负荷曲线集。接着,采用K-means聚类分别对充电负荷曲线集和光伏历史出力曲线集进行聚类,给出充电负荷和光伏出力的概率场景集,并以此为基础构建潮流分析场景集。最后,采用前推回代法进行所有场景下的配电系统潮流分析。按场景概率对潮流结果进行汇总,给出概率潮流分析结果。基于IEEE 33节点配电系统的仿真计算验证了所提模型及方法的有效性。     

含高渗透率分布式光伏的配电网故障停电损失评估

随着分布式光伏渗透率的逐步提高,配网的负荷特性发生了重大改变,传统的配网故障停电损失评估方法不再适用。提出了一种含高渗透率分布式光伏的配电网停电损失评估方法,基于典型的配网拓扑,分析了含分布式光伏的配电网负荷特性,综合运用来自营、配、调等业务领域的多源数据,构建了基于配变台区的用电负荷模型光伏发电负荷模型,并对故障停电期间的发电损失及用电损失进行了评估。实际案例的分析结果验证了该算法的有效性。     

大规模光伏发电并网概率潮流计算及对电网的影响

随着并网光伏发电容量的规模越来越大,光伏发电固有的波动性和不可控性导致其大规模并网时会使潮流分布发生变化甚至潮流反向,对电网的安全稳定运行造成影响。建立了光伏发电系统的潮流计算模型,以IEEE14节点系统和西北某省级电网系统为研究算例,对含光伏的电力系统进行概率潮流计算,全面分析了不同光伏接入容量、不同光伏接入点及不同光伏出力相关性的情况下大规模光伏并网对系统潮流的影响。结果表明光伏接入容量越大,电压及支路潮流的波动和越限概率也越大,光伏接入点将影响系统网损及光伏极限接入容量,并发现光伏接入对系统潮流的影响具有方向性,且光伏电站出力相关性不可忽略。所得结论可为电力系统新能源规划与运行提供决策参考。     

Detection and estimation of behind-the-meter photovoltaic generation based on smart meter data analytics

With the economic development and the implementation of national policies, the penetration rate of distributed photovoltaic (PV) panels, especially those behind the meter, has been greatly increased at the customers' side, which has been changing the operational landscape of the distribution network. In that regard, a critical challenge is that the PV generation behind the meter cannot be detected and measured directly by the utility company. There are even cases where customers install PV without authorization. To ensure the secure and reliable operation, the utility company has to perceive the total PV generation from smart meter data while making operational decisions to strike a balance of power supply and demand. This paper presents a novel two-stage PV detection and capacity estimation method purely based on smart meter data, which is essentially a data-driven model based on machine learning. First, given the net load curves of customers, the PV capacity features are extracted and the support vector machine (SVM) model is used to classify the customers with or without realistic PV installations. Second, based on the spatial correlation of original power demand, the total PV capacity curve is estimated by using the difference between daytime and nighttime data based on the aggregated load information. Finally, the capacity curve, along with the net load curve, is fed into Long-Short Term Memory (LSTM) model as input to estimate the real-time PV generation of individual customers.     

考虑储能-智能软开关的主动配电网混合时间尺度鲁棒优化

随着配电网中光伏(photovoltaic, PV)发电渗透率增大,由于源/荷分布不均衡引起的馈线功率急剧波动、电压越限问题时有发生。提出一种考虑储能-智能软开关(soft open point, SOP)、光伏逆变器及无功电压控制 (var/voltage control, VVC)设备的主动配电网混合时间尺度鲁棒优化方法,以提高配网运行的经济性和稳定性。首先,通过在配电网线路末端间引入储能元件与SOP相结合(E-SOP)的柔性互联装置,建立计及多种调压设备的配电网日前-日内鲁棒优化模型;其次,建立基于鲁棒条件下的时序电压灵敏度逆变器下垂控制模型,以应对PV发电随机性强所带来的风险,达到维持系统电压稳定性、平衡配电网源/荷分布的目的;最后,以改进的IEEE 33节点系统为例进行仿真算例分析,验证了所提方法的有效性。     

考虑储能-智能软开关的主动配电网混合时间尺度鲁棒优化

随着配电网中光伏(photovoltaic, PV)发电渗透率增大,由于源/荷分布不均衡引起的馈线功率急剧波动、电压越限问题时有发生。提出一种考虑储能-智能软开关(soft open point, SOP)、光伏逆变器及无功电压控制 (var/voltage control, VVC)设备的主动配电网混合时间尺度鲁棒优化方法,以提高配网运行的经济性和稳定性。首先,通过在配电网线路末端间引入储能元件与SOP相结合(E-SOP)的柔性互联装置,建立计及多种调压设备的配电网日前-日内鲁棒优化模型;其次,建立基于鲁棒条件下的时序电压灵敏度逆变器下垂控制模型,以应对PV发电随机性强所带来的风险,达到维持系统电压稳定性、平衡配电网源/荷分布的目的;最后,以改进的IEEE 33节点系统为例进行仿真算例分析,验证了所提方法的有效性。     

Efficient integration of distributed generation for meeting the increased load demand

Distributed generation (DG) can be integrated into distribution systems to meet the increasing load demand while expansion and reinforcement of these systems are faced by economical and environmental difficulties. This paper presents an efficient methodology for integration of DG power into distribution systems, in order to maximize the voltage limit loadability (i.e. the maximum loading which can be supplied by the power distribution system while the voltages at all nodes are kept within the limits). The proposed methodology is based on continuation power flow (CPF). The effectiveness of the presented methodology is demonstrated in a test distribution system that consists of 85 nodes with integration of different penetration levels of DG power. The proposed method yields efficiency in obtaining more benefits from the same amount of DG power, decreasing the losses and improving the voltage profile.     

多微电源混合系统在微电网中最优定位和规划研究

合理利用多种形式能源为负荷供电可以有效提高微电网运行经济和可靠性,然而目前微电源的前期选址定容和后期优化运行均孤立考虑,为了充分发挥其灵活供电能力,提出一种基于光伏、电池组以及柴油发电机的混合供电系统规划策略。首先,给出了光伏-电池组-柴油发电机混合供电系统能量运行方式,提高其运行经济性和灵活性;其次,提出了综合考虑多电源定位规划和运行优化的多目标优化模型,不仅减小总投资、运行维护成本、上级电网输送功率引起的网损及紧急情况引起的切负荷发生概率,同时可以使剩余能量反送给上级电网;最后,给出了基于粒子群优化人工蜂群算法改进求解方法,有效提高收敛速度。仿真结果证明,所提出的规划策略可显著提高微电网运行的经济性和可靠性。     

Optimal DG Allocation in Radial Distribution Systems with High Penetration of Non-linear Loads

This paper addresses the optimal distributed generation sizing and siting for voltage profile improvement, power losses, and total harmonic distortion (THD) reduction in a distribution network with high penetration of non-linear loads. The proposed planning methodology takes into consideration the load profile, the frequency spectrum of non-linear loads, and the technical constraints such as voltage limits at different buses (slack and load buses) of the system, feeder capacity, THD limits, and maximum penetration limit of DG units. The optimization process is based on the Genetic Algorithm (GA) method with three scenarios of objective function: system power losses, THD, and multi-objective function-based power losses and THD. This method is executed on the IEEE 31-bus system under sinusoidal and non-sinusoidal (harmonics) operating conditions including load variations within the 24-hr period. The simulation results using Matlab environment show the robustness of this method in optimal sizing and siting of DG, efficiency for improvement of voltage profile, reduction of power losses, and THD. A comparison with particle swarm optimization (PSO) method shows that the proposed method is better than PSO in reducing the power losses and THD in all suggested scenarios.     

基于无迹变换随机潮流建模的主动配电网优化调度

为了解决风电和电动汽车大量接入主动配电网所引发的随机优化调度问题,利用基于无迹变换的随机潮流计算方法处理风电出力的波动性、电动汽车充电的随机性以及电网负荷的随机波动。进而建立了以电动汽车充电功率和分布式电源出力为优化变量,以配电网运行费用最小、有功网损最小和负荷方差最小为优化目标的主动配电网随机优化模型。同时,采用多目标粒子群算法对模型进行求解,并以改进的IEEE 33节点测试系统为例对该模型进行仿真。仿真结果表明:考虑不确定性和电动汽车有序充电的优化调度模型,可以有效地减少配电网运行的成本、降低网损和缩小峰谷差,验证了所提模型的正确性和有效性。     

交直流混合配电网多阶段随机优化调度模型

高比例间歇性分布式光伏的接入给交直流混合配电网的运行带来了挑战。当前所提两阶段随机优化调度模型对不确定变量的观测较为粗略,导致配电网实时决策与日前决策偏差较大。鉴于此,提出了基于场景树的交直流混合配电网多阶段随机优化模型。所提模型以日前购电成本、日内调节成本和实时平衡成本之和最小为目标,通过储能装置的充放电功率调节、换流站输出功率调节和需求响应等灵活调节措施,实现了间歇性光伏的就地消纳和系统的削峰填谷。多阶段随机优化模型的日前离散决策变量可随日内和实时阶段的不确定信息改变而自适应调整,更符合实际高比例光伏渗透下交直流混合配电网的运行需求,为其经济灵活运行提供技术支撑。     

Influence of phasor adjustment of harmonic sources on the allowable penetration level of distributed generation

Harmonic distortion caused by increasing size of inverter-based distributed generation (DG) can give rise to power quality problems in distribution power networks. Therefore, it is very important to determine allowable DG penetration level by considering the harmonic related problems. In this study, an optimization methodology is proposed for maximizing the penetration level of DG while minimizing harmonic distortions considering different load profiles. The methodology is based on updating the voltage magnitude and angle at point of common coupling depending on the size of DG to be utilized in the harmonic power flow modeling. The harmonic parameters are determined by using decoupled harmonic power flow method, in which the harmonic source modeling with harmonic current spectrum angle adjustment is embedded, while the nonlinear loads and inverter-based DGs are connected to the distribution power network. The allowable penetration level of DGs is determined based on power quality constraints including total harmonic voltage distortion, individual harmonic voltage distortion, and RMS bus voltage limits in the optimization framework. Fuzzy-c means clustering method is also applied to decrease the computational effort of the optimization process in the long-term load profile. The effectiveness of the proposed method is illustrated on the IEEE 33-bus radial distribution network for different scenarios.     

Fundamental Study of Voltage Stability in a Power System with Large Penetration of Photovoltaic Generation Considering Induction Motor Dynamics

Because of global warming, attention to photovoltaic (PV) generation has increased, and considerable PV generation capacity will be installed in the power system. In Japan, most PV generation will be connected to the distribution system, which will cause changes in power flow in the power system. Forward power flow (flow from the higher voltage system to the lower voltage system) will be reduced and reverse power flow may occur. Because of the change in power flow, the voltage characteristics will also be changed. Consequently, it is expected that the penetration of PV generation will have some impact on voltage stability. In previous studies, the voltage characteristics in a simple power system model consisting of one infinite bus, one load, and one PV power source, have been investigated. It was found that there is not only a forward power flow limit but also a reverse power flow limit (the left nose in the PV curve), and that when the output power from PV generation is very large, the left nose sometimes has some impact on voltage stability. In this paper, the voltage stability in a simple power system model considering the dynamics of an induction motor is discussed.     

长时间尺度下计及光伏不确定性的配电网无功优化调度

针对高渗透率分布式光伏接入配电网所引起的电压控制问题,分析了无功补偿型和电压控制型两种光伏发电系统的无功电压调控特点,在考虑负荷和光伏出力不确定性的基础上,以系统总运行成本最小为目标,提出了长时间尺度下考虑电压越限风险的配电网无功优化调度模型。针对电压控制型光伏无功电压调控特点,提出了含PV类型节点的配电网概率潮流计算方法。最后,通过时间解耦并采用灾变遗传算法求解得到含高渗透率光伏的配电网长时间尺度下的无功优化调度方案。仿真算例表明:与现有光伏无功控制方法相比,所提方法能够有效降低光伏并网引起的电压越限风险,其中基于电压控制型光伏的配电网无功调度方案在降损和抑制电压波动方面的控制效果更明显。     

面向泛在电力物联网的分布式云数据中心优化选址

泛在电力物联网是应对海量综合能源设备、数据和业务计算负荷的关键,云计算是泛在电力物联网的关键技术。云数据中心是云计算架构核心,云数据中心选址对云计算性能意义重大。变电站是能量流、业务流和信息流的核心节点,且有建设数据中心的有利资源,分布式架构可以高效利用变电站资源。因此,基于变电站建设多站融合的分布式云数据中心是支持泛在电力物联网的有效方式。首先考虑能量流、业务流和信息流的关系,分析变电站特性,提出基于变电站的分布式云计算架构。然后针对该架构提出云数据中心优化选址策略。最后基于案例对优化选址策略进行仿真,证明了优化策略的有效性。     

Artificial neural networks for load flow and external equivalents studies

In this paper an artificial neural network (ANN) based methodology is proposed for (a) solving the basic load flow, (b) solving the load flow considering the reactive power limits of generation (PV) buses, (c) determining a good quality load flow starting point for ill-conditioned systems, and (d) computing static external equivalent circuits. An analysis of the input data required as well as the ANN architecture is presented. A multilayer perceptron trained with the Levenberg–Marquardt second order method is used. The proposed methodology was tested with the IEEE 30- and 57-bus, and an ill-conditioned 11-bus system. Normal operating conditions (base case) and several contingency situations including different load and generation scenarios have been considered. Simulation results show the excellent performance of the ANN for solving problems (a)–(d).     

Strategic approach for reinforcement of intermittent renewable energy sources and capacitor bank for sustainable electric power distribution system

To meet ever increasing load demand in a sustainable way, reinforcement of photovoltaic (PV) array, wind turbine (WT) and capacitor bank in distribution network is proposed in this paper. A comprehensive planning model is presented to determine location and required installation capacity of multiple PV array, WT and capacitor units in an electric power distribution network under heavy load growth situation. Intermittent power generation of renewable energy sources (RESs) are quantified with suitable probability distribution functions and incorporated in the planning model. The planning approach considers several welfare areas in the distribution systems, viz., increment of profit margin, reduction of carbon-di-oxide emission, minimization of distribution power losses, enhancement of voltage stability level and improvement of the network security considering power flow, voltage limit, line capacity, RES penetration, capacitor penetration and utility economy constraint. Non-dominated sorting based multi-objective particle swarm optimization algorithm along with fuzzy decision making criteria is used to find the best allocation alternative for mix RES and capacitor planning problem. The effectiveness of the proposed model has been tested on a typical 28-bus Indian rural distribution network. The results show that more efficient techno-eco-environmental optimization can be obtained from combined RES and capacitor planning model.     

含高渗透率分布式光伏发电系统的配电网动态等值分析

随着分布式光伏发电系统广泛接入配电网,渗透率不断升高,甚至超过了百分之一百,在光照比较强的时候会向输电网倒送功率,在这种情况下,负荷和分布式光伏发电系统共同主导了配电网的动态特性,对电网的暂态稳定产生了重要的影响。为此,建立了综合考虑负荷及分布式光伏发电系统动态特性的配电网动态等值模型,即在综合负荷模型的基础上增加一个等效的光伏电站,然后通过动态轨迹灵敏度法筛选重要参数,在DIgSILENT-MATLAB联合仿真平台上实现基于遗传算法的关键参数辨识。最后,在DIgSILENT平台中搭建了输配电网仿真算例,仿真结果表明,所提出的配电网动态等值模型能够比较准确地描述含有高渗透率分布式光伏发电系统的配电网动态特性。