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 smart distribution system reconfiguration algorithm with optimal active power scheduling considering various types of distributed generators

This paper presents an efficient way of solving the distribution system reconfiguration (DSR) problem in electrical power systems with consideration of different types of distributed generators (DGs). The objective of a DSR is to minimize the system power loss while satisfying the system constraints and keeping the topology of the system radial. In this paper, a new DSR algorithm based on a modified particle swarm optimization (PSO) is proposed to incorporate DGs with the constant voltage control mode. The proposed method is very efficient because it avoids an extra iteration loop for computing the reactive power at PV buses in order to keep the voltage at a specified magnitude. Furthermore, if the reactive power requirement is not met in between the extreme limits, the proposed algorithm strictly searches for the best possible tie switch combination to simultaneously reduce the power loss and ensure that the DGs operate in PV mode within acceptable reactive power limit. The proposed algorithm also integrates hourly DSR with optimal DG active power scheduling considering the DG type, generation limit constraints, and the allowable DG penetration level. The validity and the effectiveness of the proposed method has been tested using standard IEEE 33‐bus and 69‐bus distribution networks with various case studies. Test results show that the proposed method is robust and delivers a minimal average power loss compared with different methods, and it efficiently models DGs in DSR, demonstrating that the presence of DGs can further reduce the system loss. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

计及光伏多状态调节能力的配电网多时间尺度电压优化

随着分布式电源的渗透率逐渐增大,其本身所具有的波动性和不确定性给配电网的电能质量及其稳定性带来了巨大挑战.考虑配电网在现有慢动作调节设备难以满足无功电压调节需求的情况下,将改善因光伏随机波动性所引发的电压偏差和波动作为优化目标,提出了一种考虑分布式光伏多运行状态调节能力与传统无功调节设备相协调的配电网多时间尺度无功电压...     

Reactive Power Control of Mega‐Solar System for Voltage Regulation with Long Distribution Line

Constant power factor control of a power conditioning system in a large‐scale photovoltaic generation system (PV system) such as a mega‐solar system is introduced to mitigate voltage variations on a distribution line. However, it is difficult for the control to mitigate the voltage variation on a long distribution line because of the changes in the loss on the distribution line. This paper proposes an advanced reactive power control in which the power factor of the PV system is adjusted using both the output power of the PV system and the apparent power of loads not to minimize the voltage variation at the interconnecting point but to minimize the voltage variation over the whole distribution line. We report on the results based on numerical analysis on mitigating the voltage variation by applying this control. This paper shows that the proposed control can mitigate the voltage variation better than constant power factor control can. The proposed control has the potential to be used as a measure for suppressing voltage variations on a long distribution line.     

Impacts of load models and power factor control on optimal sizing of photovoltaic distributed generators in a distribution system

This paper studies the impact of optimal sizing of photovoltaic distributed generators (PV‐DGs) on a distribution system using different static load models (i.e., constant power, constant current, and constant impedance) and various power factor (PF) operations. A probabilistic approach with Monte Carlo simulation is proposed to obtain the optimal size of PV‐DG. Monte Carlo simulation is applied to predict the solar radiation, ambient temperatures, and load demands. The objective is to minimize average system real power losses, with the power quality constraints not exceeding the limits, i.e. voltage and total harmonic voltage distortion (THDv) at the point of common coupling (PCC). A modified Newton method and a classical harmonic flow method are employed to calculate the power flow and THDv values, respectively. An actual 51‐bus, medium‐voltage distribution system in Thailand is employed as a test case. Results demonstrate that the proposed method performs well to provide the optimal size of PV‐DG based on technical constraints. Further, the results show that the three static load models do not affect the optimal PV‐DG size but the model has a different impact for various PF operations. PV‐DGs may improve the voltage regulation and decrease the losses in distribution systems practically, but the THDv values could increase. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于RTDS储能对光伏发电PCC电压影响研究

大容量光伏发电集中并网对配电网特别是PCC电压造成一定影响,光伏电站配置适当容量的储能系统,可有效降低光伏电站PCC电压波动。本文基于RTDS建立了光储并网发电系统模型,仿真光照强度、环境温度以及邻近负荷变化,分析了PCC有无储能系统两种情况下的功率、电压有效值变化。根据电压有效值标准差数据,定量计算PCC电压波动降低幅度。仿真结果表明,储能系统可有效抑制光伏电站PCC的电压波动及逆功率运行,提高PCC电能质量。光伏出力越大,储能系统抑制PCC电压波动效果越明显。本文成果可为降低新能源PCC电压波动及大规模光储系统发展提供借鉴。     

分布式电源对配网供电电压质量的影响与改善

提出利用短路比和刚性率来评估分布式电源(distri- buted generation,DG)对配网供电电压质量影响的方法,通过仿真验证方法的可行性。并进一步具体分析旋转型分布式电源和逆变型分布式电源对系统供电电压的不同影响,分析和仿真结果证明在同等渗透率下,逆变型分布式电源对并网节点的电压影响比旋转型更小,向系统提供的短路电流也要远小于旋转型,因此在同等条件下逆变型分布式电源更加适合应用于密集负荷、高短路容量的城市配电网。并针对逆变型分布式电源抑制供电电压波动的特点,提出电压控制方法,仿真验证其同样可在一定程度上改善配电网内供电电压质量问题。     

含分布式电源的地区电网无功电压优化

随着地区电网中分布式电源的增多,一些分布式电源出力的不确定性对无功电压优化的效果影响较大.通过分析太阳能光伏发电和风力发电的模糊特性,提出建立梯形模糊数表示分布式电源出力的地区电网无功电压优化模型.将目标函数和约束条件模糊化,并利用其隶属度函数形成模糊适应度函数,通过灵敏度计算选择最有效的控制设备参与遗传操作,并且采用单点交叉算子以适应浮点数和整数混合编码.实际地区电网数据仿真结果表明所用模型和算法切实可行.     

基于模型预测控制的光伏场站快速协同无功电压控制

为解决新能源大规模接入配电网带来的电压波动及越限问题,提出了一种针对光伏场站及静止无功发生器(static var generator, SVG)接入的配电网系统动态无功电压控制方法,以实现扰动下多无功源协同调压目标。首先,分别推导了光伏场站和SVG的无功-电压控制小信号模型。其次,通过类比等效实现了不同类型无功源电压控制模型形式的统一,并结合系统电压灵敏度关系建立了系统整体电压控制模型。在此基础上考虑系统状态变化对控制参数的影响,并计及各设备无功出力约束,设计了系统模型预测控制器。最后,基于IEEE33节点系统进行仿真,验证了在光伏出力波动和负荷投切两种情况下所提方法均能够快速、有效地抑制电压波动,为有源配电网快速电压协同控制提供了理论基础。     

分布式电源对配电网电压的影响分析及其优化控制策略

针对配电网中分布式电源(DG)接入渗透率不断提高带来的电压波动、电压越限等电能质量问题,首先从理论上较全面地推导分析分布式电源接入对配电网电压的影响,包括对接入点电压和对电压分布的影响,并通过仿真对比分析了不同DG渗透率和不同DG功率因数下的电压变化情况,指出了全局电压控制的必要性。在此基础上,综合考虑配电网中分布式电源和储能的有功、无功电压调节能力,提出一种基于模型预测控制(MPC)的电压优化控制方案,通过计算各节点电压灵敏度,建立各节点电压预测模型,提前感知各节点电压变化趋势,以各节点预测电压与额定电压之间偏差最小为控制目标,实现了控制成本最低的协调电压控制策略。通过IEEE33节点配电网系统仿真算例分析,结果表明:本文提出的方法能更大限度地消除配电网中分布式可再生能源随机波动带来的影响,具有较好的电压控制灵活性和鲁棒性。     

Development of Three-Phase Unbalanced Power Flow Using PV and PQ Models for Distributed Generation and Study of the Impact of DG Models

With the increased installations of distributed generators (DGs) within power systems, load flow analysis of distribution systems needs special models and algorithms to handle multiple sources. In this paper, the development of an unbalanced three-phase load flow algorithm that can handle multiple sources is described. This software is capable of switching the DG mode of operation from constant voltage to constant power factor. The algorithm to achieve this in the presence of multiple DGs is proposed. Shipboard power systems (SPS) have other special characteristics apart from multiple sources, which make the load flow difficult to converge. The developed software is verified for a distribution system without DG using the Radial Distribution Analysis Package (RDAP). The developed software analyzes an IEEE test case and an icebreaker ship system. System studies for the IEEE 37-node feeder without the regulator show the effect of different models and varying DG penetration related to the increase in loading. System losses and voltage deviations are compared.     

A generalized power flow analysis for distribution systems with high penetration of distributed generation

In this paper, the element incidence matrix has been extended to develop a comprehensive three-phase distribution system power flow program for radial topology. Three-phase overhead or underground primary feeders and double-phase or single-phase line sections near the end of the feeder laterals have been considered. Unbalanced loads with different types including constant power, constant current and constant impedance are modeled at the system buses. Substation voltage regulator (SVR) consisting of three single phase units connected in wye or two single-phase units connected in open delta are modeled to satisfy the desired voltage level along the feeder. The mathematical model of distributed generation (DG) connected as PQ and PV buses are integrated into the power flow program to simulate the penetration of DGs in the distribution systems. The proposed method has been tested and compared with different IEEE test feeders result. The developed algorithm has been used to study the impact of both SVR and high penetration of DG on voltage profile and system power losses.     

Novel sensitivity factors for DG placement based on loss reduction and voltage improvement

This paper presents a method to select the load buses for the placement of Distributed generation (DG) based on loss reduction and voltage improvement sensitivity of the system. The strategic placement of DGs can help in reducing power losses and improving voltage profile. The proposed work discusses some new sensitivity factors that can be useful for selecting the locations. The method has the potential to be used for integrating the available DGs by identifying the best locations in a power system. The proposed method has been demonstrated on IEEE 24-bus Reliability Test System (RTS).     

Siting and Sizing of Distributed Generation and Shunt Capacitor Banks in Radial Distribution System Using Constriction Factor Particle Swarm Optimization

Abstract

This article proffers an advanced solution to allocate the distributed generation (DG) and shunt capacitor (SC) banks optimally in radial distribution system (RDS) to alleviate the power losses, revamp the voltage profile, inflate the voltage stability index, shrink the total voltage deviation, and acquire more energy savings. In the framework of finding the optimal site and size of DGs and SC banks, Particle swarm optimization (PSO) technique is modified with constriction factor and the same is aimed to apply in IEEE 33-bus system and practical Brazil 136-bus RDS. Different case studies are carried out for multiobjective problems while considering equality and inequality constraints. A comparative analysis with PSO and modified PSO is presented to project the precedence of the adopted algorithm. In addition, the obtained results are also compared to the recently surfaced few state-of-the-art algorithms to present the optimizing capability of the implemented algorithm.     

考虑电压约束的配网分布式电源准入功率研究

为了解决分布式电源接入配网的电压越限问题,首先分析了分布式电源接入对配网电压分布的影响,然后分析了对系统功率损耗的影响。利用得出的结论提出一个基于最优潮流的配网管理系统,该系统使用主动控制策略,能够在改善线路电压分布、降低系统功率损耗的基础上提高分布式电源的准入功率。     

含分布式电源的三相不平衡配电网连续潮流计算

连续潮流是电力系统电压稳定分析的重要工具。针对含不同类型分布式电源的配电网及其三相线路参数和负荷不平衡的情况,提出了一种三相配电网连续潮流方法,由切线预测环节和牛顿法校正环节组成,并采用局部几何参数化策略处理三相不平衡系统PV曲线的斜锐角现象。考虑了PV和PQ节点类型分布式电源的限值约束,给出了新的节点类型双向转换逻辑和分岔点类型识别方法。通过对IEEE 33节点配电系统进行算例仿真,表明所述算法可以有效追踪三相配电系统的PV曲线,准确计算电压稳定临界点并识别分岔点类型。     

基于三相四线制最优潮流的低压配电网光伏-储能协同控制

大规模户用光伏不平衡接入低压配电网会造成严重的电压越限、网损和三相不平衡。针对当前户用光伏消纳控制技术对三相四线制低压配电网不适用的问题,提出了一种基于三相四线制最优潮流的低压配电网光伏-储能协同控制方法。考虑电压、电流的幅值和相角,采用三相四线制节点导纳矩阵建立了低压配电网的网络拓扑结构;综合考虑网损和三相不平衡度最小,建立了储能元件有功功率和光伏逆变器无功功率的三相四线制线路多时段协同控制模型;通过复数变量拆分和模型凸化以降低三相四线制模型的求解难度,采用CPLEX算法包求出模型全局最优解。仿真结果表明,所提出的基于最优潮流的控制方法在大规模光伏和负荷不对称接入条件下能够有效抑制电压越限,同时达到降低网损、改善电网三相不平衡的目的。     

A combination of genetic algorithm and particle swarm optimization for optimal DG location and sizing in distribution systems

Distributed generation (DG) sources are becoming more prominent in distribution systems due to the incremental demands for electrical energy. Locations and capacities of DG sources have profoundly impacted on the system losses in a distribution network. In this paper, a novel combined genetic algorithm (GA)/particle swarm optimization (PSO) is presented for optimal location and sizing of DG on distribution systems. The objective is to minimize network power losses, better voltage regulation and improve the voltage stability within the frame-work of system operation and security constraints in radial distribution systems. A detailed performance analysis is carried out on 33 and 69 bus systems to demonstrate the effectiveness of the proposed methodology.     

含光伏接入的中压配电网集中调控优化策略

随着并网光伏数量和容量的增加,中压配电网电压波动及网损过大等问题日益突出。为此计及中压配电网的通信条件与计算能力等特点,提出了一种面向中压配电网的分布式光伏集中调控优化策略,抑制中压配电网电压波动及网损过大。分析光伏并网对配电网电压及网损影响,构建了以中压配电网潮流平衡方程、节点电压、支路电流及系统运行为约束,以网损最小、电压波动最小和分布式电源消纳最大为目标的多目标优化控制模型;采用商用CPLEX对模型进行求解;最后结合算例仿真对模型进行了有效性验证。结果表明,所提优化控制模型可有效降低配电网电压波动,合理分配分布式电源出力,降低网络损耗,同时保证光伏利用率处于相对合理区间。     

分布式电源接入对配电网电压变化的分析

靠近负荷侧分布式发电DG(distributed generation)系统的接入对配电网电压有着多方面影响。文中给出了一种含分布式电源的三角形负荷分布模型,并且根据电路叠加定理提出了基于此模型的电压分布计算方法。结合具体算例,研究了含分布式电源的放射状链式配电网负荷节点电压变化情况,分析了分布式电源的电压调节作用。研究结果表明,含分布式电源的三角形负荷分布模型可以有效运用于配电网的电压分布计算中;分布式电源出力及位置变化直接影响着配电系统电压水平。