An optimal allocation of distributed generation and voltage control devices for voltage regulation considering renewable energy uncertainty

Distributed generation (DG) may result in voltage fluctuation by changing line flow and reactive power injection, especially DG that generates power from renewable energy resources. To cope with this problem, this paper proposes an optimization process to optimally regulate the system voltage profile to lie close to the desired values by using the adaptive Tabu search (ATS) algorithm. The system voltages will be regulated by using dispatchable DG and voltage control devices, i.e. voltage regulator and capacitor. Moreover, probabilistic load flow calculation by using Monte Carlo simulation is chosen to evaluate the uncertainty of DG powered by renewable energy resources. The number of switching operations of the voltage regulator and capacitor are also accounted for in the optimization constraints, as excessive frequent switching operations can damage these devices. The optimal sizes and locations of dispatchable DGs and capacitors are considered as the optimization variables. The proposed method is demonstrated in an IEEE 34‐bus distribution test system and a modified 21‐bus Provincial Electricity Authority (PEA) system (Thailand). © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

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.     

Optimal sizing of photovoltaic distributed generators in a distribution system with consideration of solar radiation and harmonic distortion

This paper presents a probabilistic approach to design an optimal size of photovoltaic distributed generator (PV-DG) in a distribution system. A steady-state voltage stability index is applied to select PV-DG locations. The objective of the proposed technique is to minimize average system active power losses, while considering power quality constraints (i.e., voltage regulation, total harmonic voltage distortion, total demand distortion and harmonic currents). Monte Carlo simulation is applied to acquire solar radiations, ambient temperatures, load demands and substation voltages. The proposed technique is tested on an actual 51-bus medium voltage distribution system in Thailand. From simulations, there is a different solution between selecting the optimal size of PV-DG from with and without considering background harmonics. Also in realistic cases, PV-DGs may improve voltage regulation and decrease losses in distribution systems; however, increase total harmonic voltage distortion values.     

不同类型分布式电源在配电网中的优化布置

分布式电源接入配电网后对电网节点电压、网络潮流、网损等方面带来的影响与分布式电源的种类、接入容量及接入位置密切相关。本文基于静态负荷模型,对小水电、光伏发电两种典型分布式电源与储能设备进行了研究。通过分析不同分布式电源的稳态输出特性,将不同分布式电源的出力特征与电力系统中潮流、电压不越限等约束条件相结合,以网损最小为目标函数提出了小水电、光伏发电与储能设备的优化布置函数。结论表明考虑出力差异性后,不同分布式电源的最优布置计算结果具有明显区别,相比将分布式电源当作常规电源出力将更加精确。     

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.     

考虑电能质量的分布式电源优化配置

针对大量电力电子设备投入电网造成严重电能质量问题的现状,提出考虑谐波畸变和电压暂降损失的分布式电源(Distributed Generator,DG)优化配置方法。该方法以DG配置成本、有功损耗、电压暂降损失最小为目标函数,并在满足配网潮流等式和不等式约束的基础上增加谐波畸变限值的约束条件,建立多目标优化模型,最后采用非劣排序遗传算法(Nondominated Sorting Genetic Algorithm-II,NSGA-II)求得最优配置方案。通过IEEE 33节点配电网络对此配置算法进行仿真验证,结果证明该方法得到的DG配置方案可有效降低谐波畸变率、暂降损失及网络损耗。     

Optimal placement of DG in radial distribution systems based on new voltage stability index under load growth

This paper presents a comparison of Novel Power Loss Sensitivity, Power Stability Index (PSI), and proposed voltage stability index (VSI) methods for optimal location and sizing of distributed generation (DG) in radial distribution network. The main contribution of the paper is: (i) optimal placement of DGs based on Novel Power Loss Sensitivity and PSI methods, (ii) proposed voltage stability index method for optimal DG placement, (iii) comparison of sensitivity methods for DG location and their size calculations, (iv) optimal placement of DG in the presence of load growth, (v) impact of DG placement at combined load power factor, (vii) impact of DG on voltage stability margin improvement. Voltage profile, the real and reactive powers intake by the grid, real and reactive power flow patterns, cost of energy losses, savings in cost of energy loss and cost of power obtained from DGs are determined. The results show the importance of installing the suitable size of DG at the suitable location. The results are obtained with all sensitivity based methods on the IEEE 12-bus, modified 12-bus, 69-bus and 85-bus test systems.     

Comparison of optimal DG allocation methods in radial distribution systems based on sensitivity approaches

Integration of renewable energy based distributed generation (DG) units provides potential benefits to conventional distribution systems. The power injections from renewable DG units located close to the load centers provide an opportunity for system voltage support, reduction in energy losses, and reliability improvement. Therefore, the location of DG units should be carefully determined with the consideration of different planning incentives. This paper presents a comparison of novel, combined loss sensitivity, index vector, and voltage sensitivity index methods for optimal location and sizing of distributed generation (DG) in a distribution network. The main contribution of the paper is: (i) location of DGs based on existing sensitivity methods, (ii) proposing combined power loss sensitivity based method for DG location, (iii) modified Novel method for DG location, (iv) comparison of sensitivity methods for DG location and their size calculations, and (v) cost of losses and determining cost of power obtained from DGs and the comparison of methods at unity and lagging power factors. The results show the importance of installing the suitable size of DG at the suitable location. The results are obtained with all sensitivity based methods on the IEEE 33-bus and 69-bus systems.     

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.     

Optimal location and sizing of real power DG units to improve the voltage stability in the distribution system using ABC algorithm united with chaos

The introduction of a Distributed Generation (DG) unit in the distribution system improves the voltage profile and reduces the system losses. Optimal placement and sizing of DG units play a major role in reducing system losses and in improving voltage profile and voltage stability. This paper presents in determination of optimal location and sizing of DG units using multi objective performance index (MOPI) for enhancing the voltage stability of the radial distribution system. The different technical issues are combined using weighting coefficients and solved under various operating constraints using a Chaotic Artificial Bee Colony (CABC) algorithm. In this paper, real power DG units and constant power load model and other voltage dependent load models such as industrial, residential, and commercial are considered. The effectiveness of the proposed algorithm is validated by testing it on a 38-node and 69-node radial distribution system.     

Coordination of PV Inverters and Voltage Regulators Considering Generation Correlation and Voltage Quality Constraints for Loss Minimization

Abstract

Distributed generation sources (DGs) are widely considered as important sources of power generation in distribution systems during the last few decades. Despite the substantial benefits of DGs, increasing the penetration level of the DGs can cause dramatic voltage magnitude fluctuations. Coordination of the use of dynamic reactive power sources such as photovoltaic (PV) inverters and voltage control equipment can mitigate rapid voltage magnitude fluctuations. A coordinated volt-var control method is proposed herein to achieve the optimal expected performance (e.g., system losses) while considering the spatial correlation among PV source powers and constraining the variability of voltage magnitudes throughout the distribution network within permissible ranges. The proposed strategy formulates chance constraints on the voltage magnitude and considers the uncertainty of PV power injections over the interval of interest to maintain voltage magnitudes within acceptable limits. The proposed method has been tested on the IEEE 123-node radial distribution system for validation. Moreover, the simulation results demonstrate that the proposed method can effectively mitigate the fast voltage magnitude deviations with an acceptable reduction in system losses in the presence of intermittent renewable resources.     

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.     

分布式电源并网优化配置的图解方法

分布式电源(distributed generation,DG)除了具有调节潮流分布等常规作用外,还可被用来治理电压暂降和降低线损等。针对分布式电源引入配电网后最佳安装位置与容量计算的问题,该文基于链式配电网络、恒功率静态负荷模型和分布式电源的功率模型,并考虑DG对降低线损和调节电压的作用,提出一种图解与遗传算法相结合的计算方法。该方法采用图示求解大量方程,避免了传统算法繁琐的过程和过多的假设条件,并且通过基于电压不越界为约束的遗传算法确定分布式电源的最佳容量,有效避免了节点电压接近合格范围的上界。最后通过典型的仿真算例并与传统方法进行比较,充分证明所提方法的正确性和可行性。     

Reactive power control on residential utility-interactive PV power systems

This paper aims to optimize the reactive power absorbed by residential Photovoltaic (PV) power systems interactive with a utility feeder. Therefore, a proposed algorithm has been introduced here to assess the optimal size and location of static VAR compensator (SVC) at different operation conditions of residential PV systems. In this algorithm, a three-phase load flow analysis is used to calculate the size of SVC at different penetration levels and methods of operating PV systems, inverter power factors and load profiles to realize the substation power factor as well as PV penetration level is zero. Also, this size is optimized according to the locations to improve the voltage regulation and losses on the study feeder. The proposed algorithm is applied to develop the SVC size and location on an Egyptian utility feeder-interactive residential PV system at a constant value of power factor at the substation. Also, the effect of total reactive power on the feeder voltage and losses are deduced at different PV systems operation conditions.     

考虑分布式电源随机性的配电网最大供电能力

随着分布式电源（distributed generation, DG）越来越广泛地应用,逐渐接入到配电网中,对配电网影响举足轻重,而目前配电网最大供电能力（load supplying capability, LSC）的计算方法均未计及DG接入带来的随机性影响。针对这一问题,首先建立LSC求解模型,在蒙特卡罗模拟的概率潮流计算中考虑DG随机性,利用改进的负荷倍数法和计及电压与支路功率约束的LSC逼近法来计算配电网最大供电能力;然后通过配电网IEEE-33算例验证该模型和算法的有效性,模拟多种情景下LSC的变化,仿真结果表明DG接入配电网可提升网络静态安全裕度,且DG随机性出力影响LSC的分布特征;最后分析制约LSC提升的薄弱环节,并建议在节点电压较低处增加调压装置或无功自动补偿装置。     

Multi criteria simultaneous planning of passive filters and distributed generation simultaneously in distribution system considering nonlinear loads with adaptive bacterial foraging optimization approach

This paper presents adaptive bacterial foraging optimization (ABFO) algorithm to optimize the planning of passive power filters (PPFs) and distributed generations (DGs) in distribution system with presence of heavy nonlinear load simultaneously. The amount of nonlinear load is assumed to be serious which enforced the system planner to utilize the PPFS. Also the power loss minimization, reliability and voltage profile improvement, and other benefits encouraged the planner to employ the DGs.Some of DG technologies, such as wind generators and solar cells are based on power electronic devices and inverter implementation. Connection of this type of DGs to system produces harmonic. Therefore the utilization of PPFs among existent capacitor busses for harmonic compensation is inevitable. The objective is to minimize the power loss, the total harmonic distortion (THD) and the investment cost of PPFs and DGs simultaneously. Constraints include the voltage limits and the limit candidate buses for PPFs and DGs installation. The harmonic levels of system are obtained by current injections method and the load flow is solved by the iterative method of power sum, which is suitable for the accuracy requirements of this type of study. It is shown that through an economical planning of PPFs and DGs, the total voltage harmonic distortion and active power loss could be minimized simultaneously.     

考虑质心映射与路径解析的分布式电源优化配置搜索策略

为在配电网中优化配置分布式电源(distributed generation,DG),基于“局部–全局–局部”思想首先构造功率圈,借助物理学质心概念,搜索静力矩平衡点配置 DG;然后从全局考虑含多 DG 网络节点电压要求,结合节点电压波动指标对 DG 接入点进行区域修正,并校验功率圈内电压约束条件是否满足要求;最后解析独立 DG 等效网络,计算有效传递(影响)因子,为进一步的区域 DG 优化调度提供参考.算例结果验证了该方法的有效性     

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.     

A Multi-objective Shuffled Bat algorithm for optimal placement and sizing of multi distributed generations with different load models

In this paper a new and efficient hybrid multi-objective optimization algorithm is proposed for optimal placement and sizing of the Distributed generations (DGs) in radial distribution systems. A Multi-objective Shuffled Bat algorithm is proposed to evaluate the impact of DG placement and sizing for an optimal improvement of the distribution system with different load models. In this study, the ideal sizes and locations of DG units are found by considering the power losses, cost and voltage deviation as objective functions to minimize. Furthermore, the study is verified with voltage dependent load models like industrial, residential, commercial and mixed load models. The feasibility of the proposed technique is verified with the 33 bus distribution network and also the qualitative comparisons against a well-known technique, known as Non-dominated Sorting Genetic Algorithm II (NSGA-II) is done and results are presented.     

分布式电源接入下配电网电压无功控制效果分析

分布式电源的接入对配电网的运行状况会有很大的影响,尤其是配电网的电压分布以及网络损耗方面。首先给出了分布式电源和负荷的详细模型,通过准确建模真实模拟电网潮流变化情况。然后引入一种基于规则的电压无功控制方法,以加入分布式电源和具体负荷的IEEE13节点典型馈线系统作为仿真算例,通过电压变化曲线和系统消耗功率等指标验证该算法在分布式电源接入情况下的有效性,并分析接入分布式电源的配电网的电压无功连续控制效果。