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。     

谐波约束下的配电网接纳分布式电源能力分析

逆变型分布式电源(DG)产生的谐波直接影响了DG在配电网的渗透率,从电压畸变和电流畸变2个制约因素分析配电网中压馈线对DG接纳能力的影响。推导DG和负荷分布位置对馈线电压畸变率的作用规律,以及考虑电流畸变率影响时最不利条件下的渗透率计算公式。提出基于随机场景的仿真计算方法,针对随机场景集合采用试探寻优的方法计算渗透率。算例验证了所提方法的有效性。     

Active-reactive scheduling of activedistribution system considering interactiveload and battery storage

The increasing penetration of inverter-based distributed generations (DGs) significantly affects the fault characteristics of distribution networks. Fault analysis is a keystone for suitable protection scheme design. This paper presents the modelling methodology for distribution networks with inverter-based DGs and performs fault simulation based on the model. Firstly, a single inverter-based DG model based on the cascaded control structure is developed. Secondly, a simulation model of distribution network with two inverter-based DGs is established. Then, different fault simulations are performed based on the Real Time Digital Simulator (RTDS). Theoretical analyses are conducted to justify the simulation results, including the equivalent circuit of distribution networks with inverter-based DGs and the solution method for loop currents     

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.     

含分布式电源的配电网电压越限薄弱环节识别方法

提出一种含分布式电源(DG)的配电网电压越限薄弱环节的识别方法。对电压越限原因进行机理分析,确定导致电压越限可能的原因及其电压敏感度;定义压降比系数,提出计及网损的各节点DG/负荷最大准入容量的计算方法;研究将各节点实际接入DG容量归算至馈线末端的方法,并将其与馈线末端的最大准入容量进行比较,识别配电网中易发生电压越限的薄弱节点及越限原因;在MATLAB上搭建IEEE 33节点系统验证所提方法的有效性和正确性。     

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.     

含高渗透分布式电源配电网灵活性提升优化调度方法

高渗透率分布式电源接入配电网,加剧了配电网的波动性和不确定性,为提高配电网应对不确定扰动的能力,针对含高渗透率分布式电源配电网的灵活性提升开展研究。首先,分析了含高渗透率分布式电源配电网的灵活性需求。其次,从配电网容量灵活充裕度和分布式电源接纳的灵活适应性两个方面,提出了线路容量裕度、变压器向上容量裕度、变压器向下容量裕度、净负荷波动率、净负荷最大允许波动率5个配电网灵活性评价指标。进而构建了在灵活性指标约束下计及可中断负荷及储能的配电网灵活性提升的多目标优化调度模型。仿真结果表明,通过灵活性资源的优化调度,可以有效提升含高渗透率分布式电源的配电网灵活性,提高配电网接纳分布式电源的能力。     

Optimal reactive power control of DGs for voltage regulation of MV distribution systems using sensitivity analysis method and PSO algorithm

This paper addresses the problem of reactive power control of distributed generation (DG) units in the medium voltage (MV) distribution systems to maintain the system voltages within the predefined limits. An efficient approach for the load flow calculation is used here which is based on the topological structure of the network. It has been formulated for the radial distribution systems. A direct voltage sensitivity analysis method is developed in this paper which is also based on the topological structure of the network and independent of the network operating points. Thus, the sensitivity matrix is calculated once with the load flow program and it is used in all the system working conditions. The problem of DGs reactive power control is formulated as an optimization problem which uses the sensitivity analysis for linearizing the system around its operating points. The objective of the optimization problem is to return the system voltages inside the permitted range by using the reactive power of DGs in an optimal way. The optimal solutions are obtained by implementing particle swarm optimization (PSO) algorithm. Then, the results are verified by running a load flow considering new values of DGs reactive power. The procedure is repeated as long as a voltage violation is observed. Simulation results reveal that the proposed algorithm is capable of keeping the system voltages within the permitted limits.     

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.     

多DG不确定性建模及其对配电网谐波潮流的影响

分布式电源(DG)出力的随机性和间歇性导致其并网谐波电流具有不确定性,进而导致含DG配电网的谐波分布具有不确定性。为处理配电网谐波潮流计算中DG作为谐波源的不确定信息,以复仿射数代替点值,建立DG并网逆变器输出阻抗复仿射模型,该模型反映了直流侧电压源的不确定性对DG并网谐波电流的影响。在所提模型的基础上,改造传统确定性谐波潮流算法,提出含多DG配电网的不确定谐波潮流计算方法分析DG不确定性对谐波潮流的影响。采用典型33节点配电网算例进行仿真,与确定性分析方法计算结果的对比验证了所提方法的有效性和应用价值。     

含分布式电源配电网电压暂降仿真研究

随着大量分布式电源(DG)接入配电网,电压暂降现象将变得更为复杂。基于某地区电网实际网络构架,利用EMTDC/PSCAD建立了含分布式电源的配电网电压暂降分析模型,进行了典型算例仿真研究。仿真结果表明:逆变器型DG的接入能够在一定程度上抑制配电网电压暂降幅度和持续时间;同时,DG的控制策略、接入位置和出力都会对电压暂降产生一定的影响。     

含分布式电源的配电网电压暂降评估

运用蒙特卡洛法研究了含分布式电源的配电网电压暂降评估。分别建立了同步机型DG和逆变器型DG的仿真模型,然后基于EMTDC/PSCAD运用蒙特卡洛法对含分布式电源的典型配电网进行了仿真,采用系统平均均方根值变化频率作为评价各节点电压暂降的指标。结合多个仿真算例分析了DG的类型、控制策略、出力和接入位置对电压暂降的影响。仿真结果表明,逆变器型DG的接入能够降低配电网电压暂降的发生频次,DG的控制策略、出力和接入位置都会对电压暂降产生一定的影响,这为配置分布式电源和缓解电压暂降问题提供了参考。     

计及不确定性和谐波畸变的分布式电源最优配置

针对配网中存在谐波畸变,且存在多种不确定因素的问题,在分布式电源(distributed generator,DG)优化配置模型中考虑了谐波畸变限值,并利用区间数表示不确定因素。DG优化模型以DG成本电价、网络损耗及电压稳定性为指标,并在满足配网潮流安全性约束的基础上增加谐波畸变限值的约束,建立多目标优化模型。最后利用基于区间TOPSIS(technique for order preference by similarity to ideal solution)算法定量分析不确定因素的影响,并与非劣排序遗传算法(nondominated sorting genetic algorithm,NSGA)相结合求出DG最优配置方案。算例验证表明该方法可有效降低谐波畸变率,实现DG发电效益和供电质量的综合最优。     

Impacts of distributed generations on power system transient and voltage stability

Distributed generation (DG) units, based on their interfacing technology are divided into synchronous generator interfaced DGs, asynchronous generator interfaced DGs and inverter interfaced DGs. In this paper, the transient and voltage stability of power system with high penetration levels of the different DGs are investigated. It is assumed that all future load growth is met by adding the power generation of DGs and thus, the supplied power of main synchronous generators and load flow in transmission lines remain constant. With each penetration level of DGs, the performance of power system is studied and results are compared with the performance of power system without any DG. Simulation results will be provided in order to show the feasibility and effectiveness of our studies.     

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。     

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。     

基于SNOP的柔性配电网中分布式电源最大准入容量计算

分布式电源高比例接入配电网,将会引起配电网潮流越限等问题,影响配电网安全运行。基于智能软开关的柔性配电网为提高分布式电源消纳能力提供了新的思路。智能软开关的动态双向功率调节能力,有助于改善配电网中电压瓶颈节点和传输容量瓶颈支路的运行状态,实现全网潮流主动协同管理,从而提高柔性配电网中分布式电源准入容量。首先建立了柔性配电网中分布式电源最大准入容量模型,基于配电系统的多节点特性,该模型属于高维非线性优化问题。然后根据实际场景和参数设置的不同,分为传统配电网中分布式电源固定节点位置、柔性配电网中分布式电源固定节点位置、柔性配电网中分布式电源自由接入3种情况进行分析,并采用多种群遗传算法求解得到全局最优解。最后使用IEEE 33节点配电系统进行算例分析,结果验证了柔性配电网中智能软开关的应用对分布式电源接入能力的提升作用。所提方法在获得柔性配电网中分布式电源准入容量的同时,可从规划角度得到分布式电源接入的最优容量和位置。     

一种面向智能配电网的分布式并行电压优化方法

针对智能配电网中分布式电源(DG)接入及电网仿真实时响应的需求,提出一种分布式并行环境下求解智能配电网中各DG最优输出功率的方法,实现了快速高效的配电网电压优化。该方法首先基于凝聚层次聚类法(HAC),解决了智能配电网自动分区的问题,在此基础上,采用分布式序列二次规划(DSQP-DG)算法,通过内外层迭代交替并行求解出DG最优出力。以接入DG的IEEE 33节点系统算例对该方法进行测试验证可知,较之辅助问题原理(APP)方法,该方法具备更好的寻优能力和快速性,能够有效解决智能配电网分布式并行电压优化问题。     

光伏DG接入配电网及微电网的过电压自动调节方法研究

针对光伏DG接入配电网因过电压而导致渗透率低的问题、微电网离网运行期间过电压问题,以及微电网在非计划孤岛状态下并网转离网暂态过电压问题,提出一种P/U下垂调节方法。当光伏DG接入配电网,该方法能避免光伏DG因过电压而退出运行。当光伏DG接入离网运行微电网,因负荷减少、DG出力增加等因素而导致过电压时,该方法可以实现无通信互连线的稳态离网能量平衡。当含光伏DG的微电网在并网转离网期间,该方法能够解决暂态过电压问题。首先推导电压偏差公式并分析过电压产生机理。其次介绍P-U下垂调节方法原理。最后为验证方法可行性,以光伏DG接入配电网为算例分析对象,搭建Matlab/Simulink仿真模型,并在逆变器样机上进行试验验证。结果表明P-U下垂调节方法可行有效。