动态规划法在配电网电压无功控制中的应用

提出利用动态规划法解决配电网电压无功控制问题。基于对主变每时段的负荷、馈线每部分的负荷和主变高压侧电压的预测值，利用动态规划法（DP法）确定主变分接头、并联电容器和馈线电容器的优化动作方案，从而使配电网的网络损耗最小，主变低压倒电压与其理想值的偏差最小，主变的功率因数尽可能的高，约束条件包括主变分接头、电容器一天内最大操作次数，馈线电压允许范围，主变功率因数的允许值。为了说明这种方法的有效性，我们将其应用到沧州电力公司某变电站的部分系统中进行无功电压控制。     

主动配电网电压协调控制

分布式发电的协调控制与管理为主动配电网的主动电压调节提供了更多的技术手段,使得主动配电网的电压协调控制成为可能。分析了分布式发电对于现有配电网电压水平及其控制策略的影响,在此基础上研究并提出了主动配电网的电压分层协调控制体系及其策略。一方面利用馈线电压的精准估算,通过闭环控制逻辑实现单条馈线的电压水平实时控制,并设计了相应的主动配电网电压协调控制器;另一方面借助变电站变压器的分接头调节和电容器投切协调多馈线的电压水平,确保配网的电压质量。针对一个双馈线主动配电网的仿真试验验证了所提控制策略的有效性及实用性。     

Computation of locational and hourly maximum output of a distributed generator connected to a distribution feeder

Recently, the total number of distributed generation such as photovoltaic generation systems and wind turbine generation systems connected to a distribution network has drastically increased. Distributed generation using renewable energy can reduce the distribution loss and emission of CO₂. However, the distribution network with the distributed generators must be operated while maintaining the reliability of the power supply and power quality. In this paper, the authors propose a computational method to determine the maximum output of a distributed generator under operational constraints [(1) voltage limit, (2) line current capacity, and (3) no reverse flow to bank] at arbitrary connection points and hourly periods. In the proposed method, a three‐phase iterative load flow calculation is applied to evaluate the above operational constraints. The three‐phase iterative load flow calculation has two simple procedures: (Procedure 1) addition of load currents from the terminal node of the feeder to root one, and (Procedure 2) subtraction of voltage drop from the root node of the feeder to terminal one. In order to check the validity of the proposed method, numerical simulations are performed for a distribution system model. Furthermore, the characteristics of locational and hourly maximum output of a distributed generator connected to a distribution feeder are analyzed using several numerical examples. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 38–47, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20610     

电力电子变压器在有源配电网无功优化中的应用

尽可能地降低配电网中节点电压的偏差,是配电网运行的基本要求。为实现对节点电压的有效控制,提出利用电力电子变压器通过对其一次侧和二次侧电力电子变换器的脉宽调制控制(Pulse Width Moderation, PWM),改变其一次侧和二次侧潮流的方法加以解决。为此,构建了含分布式电源、储能元件和电力电子变压器在内的有源配电网无功优化模型,并运用粒子群优化算法进行求解。仿真结果表明,含电力电子变压器的有源配电网无功优化后的网损,低于采用有载调压变压器(On-Load Tap Changer, OLTC)对应网络无功优化后的网损;且其节点电压与额定值的相对偏差也优于后者,从而说明了在有源配电网中应用电力电子变压器,利用其灵活的无功调节功能,能提高配电网的运行水平。     

主动配电网区域自适应性电压分层分区控制

针对主动配电网集中控制周期长,调节有载变压器分接头响应速度慢,难以有效地解决局部电压越限等问题,提出一种新型电压分层分散控制方法。该方法基于多代理系统架构,以分布式电源为中心将配网划分为多个随系统运行状态变化而具有自适应性的本地控制区域,充分利用分布式电源无功输出调节能力,从而实现电压分区自治控制,并且在分散控制架构下实现与传统变压器调节手段相配合的配网综合电压调控。最后基于IEEE33节点配电测试系统对所提方法的有效性进行了分析与验证。     

Optimal voltage control in distribution systems using PV generators

Recently, renewable energy technologies such as wind turbine generators and photovoltaic systems have been introduced as distributed generation. The connection of large number of distributed generators causes voltage deviation beyond the statutory range in a distribution system. In this paper, a methodology for voltage control in proposed by using the tap changing transformers and the inverters interfaced with the distributed generators. In the proposed method, information of the voltage and power is collected via a communication network. Based on these information, the optimal reference values are calculated at the control center, and sent to the transformers and the inverters. The proposed method accomplishes a coordinated operation among the control equipments and reduces the voltage deviation. Effectiveness of the proposed method is verified by the numerical simulation results.     

基于定常海森矩阵的配电网三相最优潮流模型

含有高比例分布式电源和多种离散可调设备的主动配电网最优潮流问题,实质上是一种非凸、非线性混合整数优化问题,这类问题的求解速度较慢。文中提出了基于定常海森矩阵的配电网三相最优潮流模型,模型中考虑了三相变压器、具有三相耦合特性的分布式电源、分相调压器等设备的二次模型,以保证海森矩阵为常数。通过增加支路电流为待求变量,提出直角坐标系下三相变压器的二次模型,使优化模型的海森矩阵为常数阵,从而降低最优潮流的计算时间。构建了计及分布式电源三相功率耦合特征的配电网三相最优潮流模型,比较了二次罚函数和高斯罚函数对离散控制变量的处理效果,并应用预估—校正原对偶内点法对优化模型进行求解。同时,提出加入调压器的二级迭代最优潮流策略,从而进一步优化目标值。最后,通过算例验证了所建模型与所提方法的正确性与有效性。     

A study on cooperative tap control method for voltage profile maintenance in distribution networks with distributed generators

The introduction of distributed generators (DGs) that can utilize renewable energy is of prime importance to solve the energy and environmental issues. When a distribution network has a large number of DGs, voltage maintenance becomes a serious problem. To solve this problem, we had proposed the ‘voltage profile control method’ using reactive power control of DGs. However, the control is limited to continuous reactive power control so far, and tap control has not been considered. It is important that the conventional voltage control equipment such as the load ratio tap changer (LRT) or step voltage regulator (SVR) is utilized in order to enhance the control efficiency of the voltage profile control method. Therefore, in this paper, we develop a new method that can realize a cooperative work between inverters and tap control of LRT and SVR. The proposed method is tested in 8‐ and 24‐node model systems and its effectiveness is shown. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Optimal Control of Voltage in Distribution Systems by Voltage Reference Management

Recently, renewable energy technologies such as wind turbine generators and photovoltaic (PV) systems have been introduced as distributed generations (DGs). Connections of a large amount of distributed generations may cause voltage deviation beyond the statutory range in distribution systems. A reactive power control of DGs can be a solution of this problem, and it also has a possibility to reduce distribution loss. In this paper, we propose a control methodology of voltage profile in a distribution system using reactive power control of inverters interfaced with DGs and tap changing transformers. In the proposed method, a one-day schedule of voltage references for the control devices are determined by an optimization technique based on predicted values of load demand and PV power generation. Reactive power control of interfaced inverters is implemented within the inverter capacity without reducing active power output. The proposed method accomplishes voltage regulation within the acceptable range and reduction of distribution loss. The effectiveness of the proposed method is confirmed by simulations. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A study of centralized voltage profile control of distribution network considering dynamics of distributed generator

In a future distribution network, it will be difficult to maintain system voltage because a large number of distributed generators are introduced into the system. The authors have previously proposed a voltage profile control method using power factor control of distributed generators. When all information on the system is available, an ideal stationary solution of control orders to distributed generators is given by an optimization calculation. However, it is difficult to apply optimization control in real time because a long calculation time is required for the optimization. Therefore, it is possible that a voltage change may occur before the power factor control has finished. Thus, in this paper, we develop a new control method which can save the excessive voltage changes by taking into consideration the controlled response time of distributed generators. The proposed method was tested in a 24‐node distribution network model. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(1): 29–39, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21231     

Determination of loss‐minimum configuration with mathematical optimality in a three‐sectionalized three connected distribution feeder network

In a distribution system, in order to enhance the reliability of power supply, the distribution feeder is divided into several sections by installing sectionalizing switches, and then each of the sectionalized sections is connected to a different feeder. For example, one feeder is divided into three sections by two sectionalizing switches, and then each of the divided sections is connected to the other feeder through sectionalizing switch. Since a distribution system with many feeders has many sectionalizing switches, the system configuration is determined by states (opened or closed) of sectionalizing switches. Usually, a power utility tries to obtain distribution loss‐minimum configuration among large numbers of configuration candidates. However, it is very difficult to determine the loss‐minimum configuration such that the mathematical optimality is guaranteed, because it is well known that determination of a distribution system's configuration is to decide whether each sectionalizing switch is opened or closed by solving a combinatorial optimization problem. In this paper, the authors propose a determination method of loss‐minimum configuration by which the mathematical optimality is guaranteed for a three‐sectionalized three‐connected distribution feeder network. A problem to determine the loss‐minimum configuration is formulated as a combinatorial optimization problems with four operational constraints ( feeder capacity, voltage limit, radial structure, and three‐sectionalization). In the proposed method, after picking up all partial configurations satisfied with radial structure constraint by using enumeration method, optimal combination of partial configurations is determined under the other operational constraints by using conventional optimization method. Numerical simulations are carried out for a distribution network model with 140 sectionalizing switches in order to examine the validity of the proposed algorithm in comparison with one of conventional meta‐heuristics (tabu search). © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(1): 56– 65, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20530     

Active coordinated operation of a distribution network system for many connections of distributed generators

Recently, the total number of distributed generators (DGs) such as photovoltaic generation system and wind turbine generation system connected to an actual distribution network has increased drastically. The distribution network connected to many distributed generators must be operated keeping reliability of power supply, power quality, and loss minimization. In order to accomplish active distribution network operation to take advantage of many connections of DGs, a new coordinated operation of distribution system with many connections of DGs is necessary. In this paper, the authors propose a coordinated operation of distribution network system connected to many DGs by using newly proposed sectionalizing switch control, sending voltage control, and computation of available DG connection capability. In order to check the validity of the proposed coordinated operation of distribution system, numerical simulations using the proposed coordinated distribution system operation are carried out in a practical distribution network model. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(3): 46–57, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20655     

含固态变压器新型配电网动态无功多目标优化

风机和光伏电池等分布式电源(distributed generator, DG)大量接入配电网会导致电压波动和网损增大等问题,需要对动态无功进行优化。但是由于风光存在的不确定性会影响动态无功优化的效果,因此提出了一种含固态变压器新型配电网动态无功多目标优化方法。首先,通过 Weibull 分布和 Beta 分布对风速和光照强度进行曲线拟合,再采用风机和光伏电池出力公式生成 DG 出力模型。其次,通过蒙特卡洛仿真抽样法对上述模型进行抽样,生成上千个DG日出力场景,并采用k-means 聚类算法将上千个场景聚类成k个典型场景,以缩短随机潮流计算时间。再次,以IEEE33 节点系统为基础,建立含固态变压器有源配电网方案和含有载调压变压器有源配电网方案,以日内网损和电压波动最小为目标,采用改进型多目标灰狼算法对两种方案的相关参数进行优化。最后,以优化后的相关参数进行仿真和对比,证明了所提方法在降低配电网网损和维持节点电压稳定方面的优越性。     

分布式光伏电源极端可接入容量极限研究

为了防止大量分布式光伏电源接入配电网后可能引起电压偏差和电压波动越限,建立了负荷和分布式光伏电源引起的电压偏差和电压波动的计算模型。并在此基础上定义了分布式光伏电源极端可接入容量极限的概念,即负荷为0的极端情况下不致引起电压偏差和电压波动问题的分布式光伏电源接入容量极限。推导了6种典型分布情况下线路电压偏差和电压波动不越限时所能允许接入的极端容量极限。针对10 k V典型线路,给出了不同线型下城市配电网和农村配电网中分布式光伏电源安全接入的极端容量极限值。结果表明,分布式光伏电源极端可接入容量极限是保守的限值,只要满足该容量极限,无论分布式光伏电源和负荷的如何分布情况,都不至于对配电网产生不可接受的电压偏差或电压波动。     

A Cooperative Control Algorithm for Multiple SVRs Using Correlation of Measurement Data of Distribution Line

In this paper, a cooperative control algorithm for multiple step voltage regulator (SVR) using correlation of measurement data of distribution line is proposed. Conventionally, the control time constant of a SVR placed on the feeder end side was set slower than a SVR placed on the substation side. The unnecessary tap movement of SVR was reduced by this setting. In this case, on the condition that “the photovoltaic power generation output of the feeder end fluctuates” and “only SVR of the end side works”, it is a problem that control of SVR becomes slow. By the proposed method, the SVR settled in end side of a feeder can change its tap rapidly only if the SVR settled in sending side of a feeder will not change its tap by using proposed method. The features of the method are followings: (1) to estimate tap change possibility of the sending side SVR using correlation model of both of the SVR, (2) only use local measurement data of the SVRs for tap change control. By the proposed method, unnecessary tap change operation and lag of tap control are reduced without communication networks.     

500kV变压器调压挡位设置的指标和方法研究

对500kV变压器调压挡位的合理设置,将直接影响相关上下层电网的无功电压分布和电压水平。首先建立了变压器调挡的数学模型,分析变压器调压挡位变动时对电网无功电压的影响机理,进而提出了电压合格覆盖率指标、变压器挡位设置原则和调压挡位确定方法,最后通过对广东梅州电网的仿真计算,验证该方法进行调压挡位设置可满足各种运行方式,效果明显。     

Multi-Objective Approach for Reconfiguration of Distribution Systems with Distributed Generations

This paper presents a fuzzy multi-objective based heuristic algorithm for network reconfiguration of distribution systems considering distributed generations (DGs). The objectives of reduction of real power loss, branch current carrying capacity limit, maximum and minimum voltage constraints, and feeder load balancing are considered for performance enhancement of the distribution system. Since these objectives are non-commensurable and difficult to solve simultaneously using conventional approaches, they are converted into fuzzy domain and a fuzzy multi-objective function is formulated. A sensitivity analysis based on voltage profile improvement and real power loss reduction is used for obtaining optimal locations of DGs and genetic algorithm is used for optimal sizing of DGs. The proposed reconfiguration algorithm is implemented in two stages, initially in the first stage without incorporating DGs and in the second stage incorporating DGs for obtaining an optimal distribution system network reconfiguration. The advantage of the proposed method is demonstrated through a seventy node four feeders and a sixteen node three feeders distribution systems.     

Finding optimal SVR placement in distribution systems using power density model

In long distribution systems, Step Voltage Regulators (SVRs) are installed to regulate the system voltage. There are some papers on finding optimal placements of SVRs in the system. However, there is no analytic method that focuses on the voltage margin, that is, the optimal placement with respect to the system voltage. The authors propose a method of finding the placement of an SVR so that the voltage margin from the upper (or lower) voltage limit is the largest under heavy load. In order to deal with sets of loads that are dispersed over the entire distribution line, we derive the differential equation of the complex power and that of the voltage drop, which are expressed as functions of distance from a substation. The voltage profile is obtained as a cubic equation by solving the voltage equation if the load distribution is trapezoidal. The method of finding the optimal SVR placement distinguishes three modes with three different voltage profiles. One is the case in which the transformation ratio of the SVR is small and the system length is short, one is the case in which the transformation ratio of the SVR is large and the system length is short, and the third is the case in which the transformation ratio of the SVR is large and the system length is long. The optimal placement and tap position of the SVR are calculated by solving the above‐mentioned equations in these three modes. It is confirmed that the proposed analytical method is appropriate by model calculation results. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 11–21, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20481     

计及配电网馈线约束的电动汽车优化调度研究

随着配电网的迅速发展,其以电动汽车为代表的柔性负荷大量并入配电网,给配电网的优化运行带来挑战,电动汽车的无序充电行为会导致电力损失、电压跌落和馈线过载等一系列问题。以电动汽车充电费用和电池衰减成本以及系统发电成本最低为目标,并考虑配电网的馈线容量耦合约束,提出了一种基于交替方向乘子法(Alternating Direction Method of Multipliers,ADMM)的电动汽车分散式优化调度策略。在仿真案例中验证了所提算法的最优性,并表明了该方法能够有效地解决配电网馈线过载问题。     

考虑电压调整约束的多个分布式电源准入功率计算

针对分布式电源准入容量计算的问题,提出了考虑电压调整约束后的准入功率优化计算模型。该模型的特点是能够模拟有载调压变压器、分布式电源事故停运以及多个分布式电源的情况。对于多个分布式电源接入的情况提出了至少准入功率的概念。根据双层优化理论,建立了以准入功率最大化为上层优化目标、满足电压约束为下层优化目标的计算模型。通过112节点系统的算例分析,结果表明所提出的准入功率计算模型是有效可用的。另外,算例还分析了分布式电源接入位置对准入功率的影响。