Hybrid GA and OPF evaluation of network capacity for distributed generation connections

Many methods have been applied to examine the capacity of existing distribution networks to accept distributed generation (DG). One aspect missing from existing approaches is the capability to efficiently site and size a predefined number of DGs. Here, a hybrid method employing genetic algorithms and optimal power flow aims to overcome this shortcoming. It could be applied by distribution network operators to search a network for the best sites and capacities available to strategically connect a defined number of DGs among a large number of potential combinations. Some applications of the proposed methodology in the UK under current Ofgem financial incentives for DNOs confirmed its effectiveness in siting and sizing an assigned number of DG units.     

含分布式电源的配电网无功优化

为提高系统电压稳定性,在传统无功优化目标函数模型的基础上引入电压稳定L指标,将电压稳定L指标与最优潮流结合,建立了考虑网络损耗和系统电压稳定的配电网无功优化模型.在小生境遗传算法的基础上,对遗传算法小生境进行单纯形搜索,消除算法中存在的早熟收敛和开采能力不足的缺点,增强了算法的寻优能力.采用IEEE33节点算例分析表明,该算法优化效果良好,能有效降低有功网损,提高系统电压稳定性。     

基于网损二阶灵敏度的分布式电源出力鲁棒优化方法

随着分布式电源大量分散接入配电网,一方面造成了配电网网损增加,另一方面,其出力的波动性造成了分布式电源消纳困难。为此,本文提出了基于二阶灵敏度网损的分布式电源出力鲁棒优化方法。首先,通过泰勒展开推导了基于二阶灵敏度的有功网损和无功网损计算公式,并将其嵌入到分布式电源出力优化模型中,建立了以综合网损最小和分布式电源出力最大化的优化模型;然后,采用多面体不确定性集合来描述分布式电源出力,构造了分布式电源出力的鲁棒优化模型,通过对偶变换将将鲁棒优化模型转化为确定性的二次规划模型。最后,通过70节点配电系统仿真结果表明,本文所提出的二阶灵敏度的网损计算方法误差较小,最大仅为5%,鲁棒优化方法可以通过多面体维数控制保守性,优化效率高。     

Intelligent power management strategy of hybrid distributed generation system

This paper describes a novel control strategy for active power flow in a hybrid fuel cell/battery distributed generation system. The method introduces an on-line power management by a hierarchical hybrid controller between dual energy sources that consist of a battery bank and a solid oxide fuel cell (SOFC). The proposed method includes an advance supervisory controller in the first layer which captures all of the possible operation modes. This layer has been developed by Stateflow toolbox and prepares a proper supervisory environment for this complex structure. In the second layer, an advanced fuzzy controller has been developed for power splitting between battery and fuel cell. With regards to the operation modes, the upper layer makes decision to choose the switching chain rules and corresponding controller in the second layer. Finally in the third layer, there are local controllers to regulate the set points of each subsystems to reach the best performance and acceptable operation indexes. Simulation results of a test system illustrate improvement in the operation efficiency of the hybrid system and the battery state of charge has been maintained at a reasonable level.     

含分布式电源的DEIWO算法配电网无功优化

针对含分布式电源的配电网无功优化的特点,提出一种将入侵杂草算法与差分进化算法相结合的混合求解算法。该算法将一组初始可行解进行繁殖、空间扩散,当达到环境允许的最大值时,通过引入竞争机制,选取适应度较高的部分个体,再通过变异、交叉、选择,最终保留最佳个体。该算法既利用了入侵杂草算法结构简单、参数少和鲁棒性强的优点,又通过结合差分进化算法,克服其易陷入局部最优,精度不高的缺陷。以IEEE33节点系统进行仿真分析,并与传统的入侵杂草优化算法进行比较,结果表明该算法具有较强的全局搜索能力以及较高的收敛精度,能够有效地减少功率损耗。     

主动配电网的分布式电源优化规划方案研究

主动配电网(ADN)模式是一种可以优化利用分布式能源资源的技术解决方案。在评估主动配电网的分布式电源接入方案时,计及分布式电源的发电效益成本以及其对电网运行影响的基础上,考虑分布式电源的减排指标,构建主动配电网低碳优化目标函数模型。在各指标权重赋值时,为避免造成人为主观性过强,根据1-9标度法,通过一致性校验形成判断矩阵,得到合理的权重系数。其次,为体现各指标变化趋势并具有一定区分度,采用隶属度函数对各指标值进行隶属化,将各自的效益值隶属化后与对应的权重加权。最后,基于遗传算法对IEEE14节点算例开展方案分析,得出分布式电源的优化规划方案,结果表明所提出的低碳优化模型合理有效。     

Application of a simplified Grey Wolf optimization technique for adaptive fuzzy PID controller design for frequency regulation of a distributed power generation system

A Simplified Grey Wolf Optimizer (SGWO) is suggested for resolving optimization tasks. The simplification in the original Grey Wolf Optimizer (GWO) method is introduced by ignoring the worst category wolves while giving priority to the better wolves during the search process. The advantage of the presented SGWO over GWO is a better solution taking less execution time and is demonstrated by taking unimodal, multimodal, and fixed dimension test functions. The results are also contrasted to the Gravitational Search Algorithm, the Particle Swarm Optimization, and the Sine Cosine Algorithm and this shows the superiority of the proposed SGWO technique. Practical application in a Distributed Power Generation System (DPGS) with energy storage is then considered by designing an Adaptive Fuzzy PID (AFPID) controller using the suggested SGWO method for frequency control. The DPGS contains renewable generation such as photovoltaic, wind, and storage elements such as battery and flywheel, in addition to plug-in electric vehicles. It is demonstrated that the SGWO method is superior to the GWO method in the optimal controller design task. It is also seen that SGWO based AFPID controller is highly efficacious in regulating the frequency compared to the standard PID controller. A sensitivity study is also performed to examine the impact of the unpredictability in the parameters of the investigated system on system performance. Finally, the novelty of the paper is demonstrated by comparing with the existing publications in an extensively used two-area test system.     

基于细菌菌落优化算法分布式电源优化配置

分布式电源位置和容量的优化配置可确保其发挥更好的技术经济效用。在分析DG特性的基础上,建立了考虑含分布式电源的有功网损费用最小和综合投资成本以及购电成本最小模型的多目标优化模型,并且提出了一种新颖的智能优化算法细菌菌落算法。细菌菌落优化算法根据单个细菌的生长方式及其群体菌落繁殖的特性演化而来。该算法建立了细菌菌落的生成和死亡的寻优机制,并提供了一种新的寻优算法的结束方式。最后,通过算例验证所提算法具有良好实用性和适应性,并且也验证所提模型的实际意义。     

Disturbance detection in grid-connected distributed generation system using wavelet and S-transform

In this paper, wavelet transform and S-transform based approach is proposed for islanding detection and disturbance due to load rejection in distributed generation (DG) based hybrid system. The two types of distributed generation technology: inverter based and rotating machine based, that consists of photovoltaic, fuel cell and wind systems are considered in hybrid system configuration. The negative sequence voltage signal is analyzed through wavelet transform and S-transform for islanding detection of these resources from the grid. The above two approaches are also used in study of voltage profile at point of common coupling (PCC) with a non-linear load connected. The study for different scenarios in operation of DG system is presented in the form of time-frequency analysis. The energy content and standard deviation (STD) of S-transform contour and wavelet transform signal is also reported for both islanding detection and disturbance due to load rejection.     

含分布式发电的配电网多目标无功优化策略研究

为以最省的无功设备投资、最大限度地保证系统经济运行,增加解决问题的灵活性,研究了含分布式发电(DG)的配电网多目标无功优化策略,即构建含DG的配电网多目标无功优化模型。运用自适应多目标粒子群(AMOPSO)算法求解此问题,一改传统将多目标问题转化为单目标求解的做法。为验证所提策略,以含DG的IEEE 33节点系统为例,将AMOPSO应用于以最小化系统有功网损和最小化无功补偿设备容量（投资）为目标函数的多目标无功优化问题。仿真表明,采用该策略为决策者提供了可供选择的多样性解;优化结果验证了所建多目标模型的优越性和所提算法应用的可行性和有效性。     

Energy losses in a distribution line with distributed generation based on stochastic power flow

This paper proposes a methodology for stochastic power flow in a distribution line with dispersed photovoltaic (PV) penetration. Both load and PV generation are stochastic processes. The methodology uses a probabilistic model for load demand based on measured data and an extensive stochastic modeling of PV units’ power production based on historical meteorological data and commercial available PV panels. Annual power flow simulations are performed to evaluate loss reduction resulting for different penetration levels and siting strategies of PV into an urban radial distribution feeder. Finally, a cost index for the losses is defined taking into account System Marginal Price data. Results may be of interest for dimensioning, siting and cost allocation in distribution systems with dispersed generation.     

含分布式电源的配电网优化运行研究

针对分布式能源大规模接入配电网带来的配电网规划和电能质量等问题,进行配电网优化运行研究。从分布式电源给配电网带来的影响出发,对配电网重构技术、分布式电源位置和容量优化及滤波器选型和位置优化三个角度进行了综述,同时分析总结配电网优化运行的建模方式和约束条件,并围绕多目标非线性且多约束的组合优化问题求解算法进行了梳理归纳,对配电网优化运行做总结与展望。     

On the appropriate monitoring period for voltage flicker measurement in the presence of distributed generation

Voltage flicker or voltage fluctuations are considered a major power quality problem causing temperature rise, generators and motors overloading and affecting humans through the irritating light flicker. It is expected that the level of voltage flicker will increase due to the increased penetration of distributed generation (DG) in the distribution system. Site monitoring is required to make sure that the level of voltage flicker is within the allowed limit. In order to determine the appropriate monitoring period for voltage flicker measurement while considering DGs, two case studies were considered in the paper; 1 week and 1 day monitoring periods. The results reveal that a monitoring period of 1 week may be very long especially in the presence of DG and it may hide valuable information. On the other hand a 1-day monitoring period is more appropriate in these situations. Therefore it is recommended to use 1-day monitoring period instead of 1 week especially in the presence of DG.     

Distributed generation modeling for power flow studies and a three-phase unbalanced power flow solution for radial distribution systems considering distributed generation

Distributed generations (DGs) are generally modeled as PV or PQ nodes in power flow studies (PFSs) for distribution system. Determining a suitable model for each DG unit requires knowing the DG operation and the type of its connection to the grid (direct or indirect). In this respect, this paper offers a helpful list of DG models for PFSs. Moreover, an unbalanced three-phase power flow algorithm for radial distribution networks considering DG is presented based on the power summation method in backward/forward sweep technique. The proposed algorithm is simple and fast and can handle DG units in both PV and PQ mode. In comparison with the current analysis methods, handling of PV nodes in the proposed method is very simple since it uses active and reactive powers as flow variables rather than the complex currents and then checks the limits of reactive power of the generator of PV node straightforwardly. IEEE four-node test feeder is used to validate the proposed method. IEEE 13-node test feeder without regulator and with different DG models is analyzed and the results are presented. Moreover, the results are compared with and without considering system losses.     

计及多种分布式能源运行的配电网双层优化规划方法

在配电网分布式可再生能源(Renewable Distributed Generation, RDG)优化规划问题上,考虑可控分布式电源和可中断负荷的调度运行情况,建立RDG双层优化模型。上层模型以配电网系统电压偏移最小、网络损耗最小为目标,求解RDG接入配电网的最优位置和容量。下层模型以配电网发电综合运行成本最小为目标,求解各时段可控分布式电源和可中断负荷最优出力安排。利用场景分析方法处理多种分布式可再生能源优化中的不确定因素。为减少模型计算量,采用K-means聚类算法获取典型场景。最后,采用改进的自适应遗传算法求解,以IEEE-33节点网络系统为例对所提模型与方法的有效性进行验证。仿真结果表明,该方法能够有效提高RDG优化方案在系统实际运行中的适用性。     

计及UPFC的电力系统网损优化控制研究

将统一潮流控制器(UPFC)等效为节点附加注入功率,控制变量增加了UPFC等值模型中串联电压源电压的幅值和相位,以及并联电流源电流的无功分量等控制参数,建立计及UPFC的无功优化模型。由UPFC控制参数与安装线路的电流和端点电压,推导出UPFC运行容量计算公式,结合UPFC价格与容量函数关系,确立UPFC参数与价格的数学关系,将其应用于无功优化研究,以收益最大为目标函数,分析UPFC的降损经济效益。以IEEE30节点系统为例进行仿真分析,结果表明,UPFC不仅具有良好的降损特性,而且获得的收益能够弥补自身价格昂贵的不足,具有实际应用价值。     

节能发电调度的网厂两级优化方案

节能发电调度是具有多目标、多约束特性的大系统优化问题.针对集中调度方案中可能出现的计算工作最大、实时性差、机组在线煤耗特性获取困难、故障时对系统影响大等问题,提出节能发电调度的网厂两级优化办案,其中电网侧综合电网安全稳定性及经济性给出厂级负荷指令,电厂侧根据机组实际煤耗特性及运行状态实现二次优化分配.理论分析表明,两级调度方案比集中调度方案具有更好的节能效果,兼顾了当前电网调度现状与网厂双方利益,是一种行之有效的可实施方案.     

基于多目标优化模型的分布式电源选址方案研究

分布式电源接入配电网是智能电网的关键。分布式电源接入配电网的位置及所注入的容量会对电网的损耗和电压的稳定性产生影响。采用多目标优化模型研究分布式电源优化选址问题。在综合考虑电压稳定的两类指标以及电网损耗的基础上,建立了多目标的优化仿真模型。同时,利用多岛遗传算法进行全局寻优求解,提高了全局最优解的可能性。对于多目标优化的可行解,运用Pareto最优解分析理论,使模型更具有实际工程意义。最后,采用配电网的标准算例对模型及算法进行了验证。表明,该模型具有优异的优化效果,有助于工程的实际应用。     

Optimal siting and sizing of distributed generation accompanied by reconfiguration of distribution networks for maximum loss reduction by using a new UVDA-based heuristic method

A great number of methods have been proposed for distributed generation (DG) placement in distribution networks to minimize the power loss of Medium Voltage (MV) lines. However, very few researches have been done for network configuration in parallel with the DG siting and sizing for the maximum system loss reduction. In this paper, a heuristic method based on “uniform voltage distribution based constructive reconfiguration algorithm” (UVDA) is proposed for the simultaneous reconfiguration and DG siting and sizing. The results obtained from the application of the proposed method on two well-known distribution networks and a real network clearly verify the robustness of the contributed technique. The simulation results demonstrate that the proposed approach is able to find the best solution of the problem found so far. Also, the presented method is applicable to real large-scale distribution systems to find the optimal solution in a very short period of time.     

Distribution network expansion considering distributed generation and storage units using modified PSO algorithm

Multistage distribution network expansion because of load growth is a complex problem in distribution planning. The problem includes minimizing cost of objective function subject to technical constraints. The objective function consists of investment, operation and reliability costs. In this paper, HV/MV substations, main and reserve MV feeders, dispatchable DG sources and storage units are considered as possible solutions for multistage distribution expansion planning. A three-load level is used for variable load and some strategies are proposed for DG and storage units operation. A modified PSO algorithm is applied to solve the complex optimization problem. Numerical results of the case studies show the ability of the modification. Moreover, the proposed strategies improve the distribution network from both economical and reliability points of view compared with the other methods.