Impact of distributed generation on distribution contingency analysis

Alternative energy sources are becoming more cost effective, and many utilities are now providing incentives for alternative power. Placing these alternative energy sources, as well as other smaller traditional energy sources, on the distribution power system, allows the development of a new paradigm related to distributed generation (DG). The size and site of the DG will have an effect on the voltages and operations of the distribution power system in the future. This paper discusses a procedure for evaluating the impact of site and size on both the original distribution power system as well as a reconfigured power system after a fault. Validation of this work is done using the IEEE 37 node distribution feeder and the results and trends are presented.     

Impact of the penetration of distributed generation on optimal reactive power dispatch

Optimal reactive power dispatch (ORPD) is a complex and non-linear problem, and is one of the sub-problems of optimal power flow (OPF) in a power system. ORPD is formulated as a single-objective problem to minimize the active power loss in a transmission system. In this work, power from distributed generation (DG) is integrated into a conventional power system and the ORPD problem is solved to minimize transmission line power loss. It proves that the application of DG not only contributes to power loss minimization and improvement of system stability but also reduces energy consumption from the conventional sources. A recently proposed meta-heuristic algorithm known as the JAYA algorithm is applied to the standard IEEE 14, 30, 57 and 118 bus systems to solve the newly developed ORPD problem with the incorporation of DG. The simulation results prove the superiority of the JAYA algorithm over others. The respective optimal values of DG power that should be injected into the four IEEE test systems to obtain the minimum transmission line power losses are also provided.     

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.     

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.     

Optimization of biomass fuelled systems for distributed power generation using Particle Swarm Optimization

With sufficient territory and abundant biomass resources Spain appears to have suitable conditions to develop biomass utilization technologies. As an important decentralized power technology, biomass gasification and power generation has a potential market in making use of biomass wastes. This paper addresses biomass fuelled generation of electricity in the specific aspect of finding the best location and the supply area of the electric generation plant for three alternative technologies (gas motor, gas turbine and fuel cell-microturbine hybrid power cycle), taking into account the variables involved in the problem, such as the local distribution of biomass resources, transportation costs, distance to existing electric lines, etc. For each technology, not only optimal location and supply area of the biomass plant, but also net present value and generated electric power are determined by an own binary variant of Particle Swarm Optimization (PSO). According to the values derived from the optimization algorithm, the most profitable technology can be chosen. Computer simulations show the good performance of the proposed binary PSO algorithm to optimize biomass fuelled systems for distributed power generation.     

Efficient integration of distributed generation for meeting the increased load demand

Distributed generation (DG) can be integrated into distribution systems to meet the increasing load demand while expansion and reinforcement of these systems are faced by economical and environmental difficulties. This paper presents an efficient methodology for integration of DG power into distribution systems, in order to maximize the voltage limit loadability (i.e. the maximum loading which can be supplied by the power distribution system while the voltages at all nodes are kept within the limits). The proposed methodology is based on continuation power flow (CPF). The effectiveness of the presented methodology is demonstrated in a test distribution system that consists of 85 nodes with integration of different penetration levels of DG power. The proposed method yields efficiency in obtaining more benefits from the same amount of DG power, decreasing the losses and improving the voltage profile.     

Optimum allocation of the maximum possible distributed generation penetration in a distribution network

In this paper a method is proposed to determine the optimum allocation of the maximum distributed generation penetration in medium voltage power distribution networks. The method is based on an already-known but suitably modified and optimized method. Technical constraints, such as thermal rating, transformer capacity, voltage profile and short-circuit level are considered. A real network with already installed distributed generation resources is examined as a case study. The type, locations and ratings of these resources are predetermined. The satisfaction of the aforementioned technical constraints is examined initially in the framework of the existing network situation. The problems observed are solved by applying the required modifications in the network structure. Next, the proposed method is used to determine the optimum allocation of the maximum distributed generation penetration either in the predetermined network buses or in other random buses, in order to overcome the technical problems, without changing the network structure. Finally, the results are suitably estimated and extended in order to allow for more general conclusions concerning real power distribution networks.     

基于分布式电源有功无功调节能力的配电网无功规划

传统的无功规划方法在应对小概率极端电压场景时往往要求配电网投资大量的无功补偿装置。为此,基于分布式电源及负荷场景,提出一种配电网无功规划模型,该模型充分利用了分布式电源的有功、无功调节能力,在小概率极端电压场景下将分布式电源有功调节作为一种附加电压调节手段,并以无功补偿装置投资费用和分布式电源有功调节费用之和最小为目标以减少系统总支付费用。提出一种嵌入原始对偶内点法的粒子群优化算法对模型进行求解。通过对自定义IEEE 30节点系统进行仿真分析,验证了所提模型的经济性和所提算法的有效性。     

微网中分布式电源变动对其谐波的影响分析

为了掌握微网中谐波的变化规律,降低谐波危害,基于DIgSILENT/Power Factory仿真平台,搭建了适合于谐波分析的微网模型。仿真分析了分布式电源在不同容量、不同接入位置微网系统的谐波变化,并通过风电和光伏两种分布式电源进行验证,发现了微网谐波变化的一定规律,给出了相关建议,对今后的微网谐波治理工作具有一定的参考价值。     

Fast harmonic simulation method for the analysis of network losses with converter-connected distributed generation

The use of distributed generation (DG) in low voltage grids is becoming more common. The impact of the DG units is considered, with an emphasis on the effect of DG on the network losses. These losses consist of fundamental and harmonic losses. The converter-connected DG units have a different influence on these two terms of the total losses. The aim of this paper is to present a fast harmonic simulation model that can be applied to study the influence of a DG unit on the total losses and elucidate the importance of the harmonic losses in proportion to the total losses.     

Optimization of distributed generation systems using a new discrete PSO and OPF

Many methods have been applied to achieve optimal site and size of distributed generation systems. This paper introduces a new hybrid method, which employs discrete particle swarm optimization and optimal power flow to overcome this shortcoming. The main technical constraints are imposed for utilities, which could apply this approach to search the best sites to connect distributed generation systems in a distribution network choosing among a large number of potential combinations. A fair comparison between the proposed algorithm and other methods is performed. For such goal, convergence curves of objective function versus number of iterations are computed. The proposed algorithm reaches a better solution than Genetic Algorithms considering similar number of evaluations.     

Integrating distributed generation into electric power systems: A review of drivers,challenges and opportunities

It is now more than a decade since distributed generation (DG) began to excite major interest amongst electric power system planners and operators, energy policy makers and regulators as well as developers. This paper presents an overview of the key issues concerning the integration of distributed generation into electric power systems that are of most interest today. The main drivers behind the focus on DG integration, especially of the renewable type, in many countries around the world are discussed. A synopsis of the main challenges that must be overcome in the process is presented. Particular emphasis is placed on the need to move away from the fit and forget approach of connecting DG to electric power systems to a policy of integrating DG into power system planning and operation through active management of distribution networks and application of other novel concepts. The paper also analyses the repercussions in transmission system operation and expansion that result from the connection of large amounts of DG of different energy conversion systems focusing on issues related with impacts in steady state operation, contingency analysis, protection coordination as well as dynamic behaviour analysis. A discussion on the possibility of provision of ancillary services by DG is also included. Some results from studies performed in the interconnected Portuguese transmission system are presented and discussed. Some of the opportunities that could be exploited in support of the integration and hence greater penetration of DG into electric power systems are also explored.     

Assessment of maximum distributed generation penetration levels in low voltage networks using a probabilistic approach

The main objective of network planning is to determine the technically and economically optimal solution that will ensure continuity of supply and adequate power quality as well as allow further integration of distributed generation (DG), despite its substantial impact on the network performance. The maximum DG penetration level also has to be planned or at least assessed, and is heavily dependent on the DG location and size and on the voltage control method. The paper presents a probabilistic approach to network planning, which has many advantages compared to the traditional approaches using estimated peak values and empirically defined simultaneity factors. The method enables the evaluation of the future voltage conditions and therefore the comparison of different network development scenarios, taking into account the stochastic natures of future DG location and loads consumption. By analyzing different solutions, it is possible to minimize the necessary investments in the network. The planning method is presented on an actual low-voltage (LV) distribution network, but it can be used also in medium-voltage (MV) network planning as well.     

Insulation coordination associated with distributed generation connected at distribution level

Insulation coordination is defined as the selection of dielectric strength of equipment, taking into account the over-voltages that could appear in the utility system and with the presence of protective devices. Electromagnetic transient (EMT) over-voltages are regarded as disturbances due to lightning surges and switching surges that result in the disruption and possible damage to equipments. The principal subject of this paper is to perform insulation coordination on the distributed generation (DG) by using methods of modeling lightning surges and switching surges. PSCAD/EMTDC is the main software used for the modeling and simulations.     

分布式电源准入容量对电力系统的影响分析

探讨了不同电压调整方法对分布式电源接入系统后准入容量的影响并进行了仿真模拟,运用二分法算法,结合IEEE-112节点系统的算例对各种模型进行了求解并分析计算了分散电源事故解列前后的准入容量,证明模型的合理有效性.     

大量分布式光伏电源接入智能配电网后的能量渗透率研究

从容量渗透率角度分析了并网光伏电源对传统配电网的影响,研究了在传统配电网最小负荷限制下光伏并网的容量渗透率极限。从能量渗透率角度分析了分布式光伏电源利用率、成本等随光伏接入容量增加的变化趋势,在此基础上提出利用负荷转移和储能技术来增强配电网光伏接纳能力的措施。仿真结果表明,所提措施都能提高光伏能量渗透率和光伏利用率,但储能技术效果更好,且随着能量渗透率的增大,储能技术的优势更明显。     

Implementation of the shunt harmonic voltages compensation approach

Instead of injecting harmonic currents to compensate those drawn by distorting loads, in this paper a shunt active filter is used for generating harmonic voltages to compensate harmonic voltages at the point of common coupling; the main advantage in using such a compensation approach is that, when the aim is to reduce or eliminate the harmonic voltages at the point of common coupling only one active filter is required. For determining the harmonic voltages such a filter must generate, two simple and practical methods are proposed in this paper; the effectiveness of these methods was evaluated using a 1-kW prototype of an active filter operating according to the shunt harmonic voltage compensation approach. In addition, the laboratory results were comparable to those obtained with the ATP-EMTP simulation software.     

分布松弛节点法在发电偏离电量研究中的应用

针对电力市场环境下经济补偿分析的需要,采用分布式松弛节点的超解耦潮流算法对某实际电网发电偏离电量的现象进行了模拟分析计算.通过计算并动态调整各个调节电厂和联络线的调节分配因子,得到比单个松弛节点计算时更加实际的潮流变化.以上数值方法经实际运行,证明是切实可行的.     

Optimized restoration of combined ac/dc shipboard power systems including distributed generation and islanding techniques

Reconfiguration involves changing the status (OFF/ON) of switches, and reconfiguration for restoration involves changing the switch status to maximize the supply to loads that are left unsupplied after fault removal. Shipboard Power Systems (SPS) need automated reconfiguration for restoration schemes to restore vital loads quickly and efficiently in order to improve fight-through and survivability capabilities. The restoration in this paper is achieved using optimization with multiple objectives—maximizing the restored load and giving priority to vital loads. A restoration scheme for SPS with an integrated power system (IPS) and distributed generation (DG) involving islanding has been developed. This formulation includes a hybrid power system that has both ac and dc parts. The restoration formulation in this paper also considers the unbalanced nature of SPS operation with mutual coupling.     

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.