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.     

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.     

Short-circuit calculations in networks with distributed generation

Fault level considerations may be an inhibiting factor for the interconnection of distributed generation (DG) to the network, particularly at the medium voltage level. In this paper, the latest edition of the IEC 60909 Standard is applied for the calculation of the resulting fault level in medium and low voltage distribution networks with DG. First, an outline of the IEC calculation methodology is presented, including all relevant equations for DG cases studies. Then the short-circuit contribution of the various DG types is extensively discussed. The application of the methodology is demonstrated on a study case medium voltage distribution network, which includes all representative types of DG sources. Emphasis is placed on the contribution of the upstream system, which is the dominant source of short-circuit current. A discussion is also included on potential measures for fault level reduction.     

Bi-level stackelberg game-based distribution system expansion planning model considering long-term renewable energy contracts

With the deregulation of electricity market in distribution systems, renewable distributed generations (RDG) are being invested in by third-party social capital, such as distributed generations operators (DGOs) and load aggregators (LAs). However, their arbitrary RDG investment and electricity trading behavior can bring great challenges to distribution system planning. In this paper, to reduce distribution system investment, a distribution system expansion planning model based on a bi-level Stackelberg game is proposed for the distribution system operator (DSO) to guide this social capital to make suitable RDG investment. In the proposed model, DSO is the leader, while DGOs and LAs are the followers. In the upper level, the DSO determines the expansion planning scheme including investments in substations and lines, and optimizes the variables provided for followers, such as RDG locations and contract prices. In the lower level, DGOs determine the RDG capacity and electricity trading strategy based on the RDG locations and contract prices, while LAs determine the RDG capacity, demand response and electricity trading strategy based on contract prices. The capacity information of the DRG is sent to the DSO for decision-making on expansion planning. To reduce the cost and risk of multiple agents, two long-term renewable energy contracts are introduced for the electricity trading. Conditional value-at-risk method is used to quantify the RDG investment risk of DGOs and LAs with diferent risk preferences. The efectiveness of the proposed model and method is verifed by studies using the Portugal 54-bus system.     

基于免疫遗传算法的含分布式电源配网规划

大量分布式电源的接入使配电网规划更加复杂.在限制分布式电源接入总量和考虑多种约束的基础上,建立以配网年费用最小为目标函数的规划模型.针对该模型的特点,采用一种新型免疫遗传算法( IGA)对配电网扩展规划进行优化.该算法综合了免疫系统和遗传算法的优点,可实现群体收敛性和个体多样性间的动态平衡,具有良好的全局收敛能力.分别...     

主动配电网双层实时优化博弈研究

随着分布式电源(DG)的广泛接入及配电侧市场改革的不断深化,DG运营商成为配电网中新增的利益主体,研究DG运营商作为独立主体参与下的配电侧市场交易和竞价机制具有重要意义。文中构建了一个考虑DG运营商和配电公司不同利益主体需求的双层交易模型。该模型的上层为配电网购电策略的制定,下层为DG运营商根据配电公司购买电价所做出的出售功率响应。上层以电网的安全经济运行为目标,决策变量是从上级主网购买的电量,向分布式电源制定电价和负荷中断量;下层以DG运营商的经济收益最大化为目标,决策变量为DG运营商的最优出力。考虑到双层模型的耦合性,文中利用原始-对偶算法将双层优化模型转化为单层模型,并将非线性潮流约束进行二阶锥转化。算例分析表明所述模型可以反映主动配电网与DG运营商的利益博弈关系,并有效指导双方交易电价的确定。     

Integrated distribution network expansion planning incorporating distributed generation considering uncertainties,reliability, and operational conditions

In this paper, an integrated methodology is proposed for distribution network expansion planning which considers most of the planning alternatives. The planning aims to determine the optimal reinforcement of existing medium voltage lines and high voltage/medium voltage substations, or installation of new ones to meet the load growth in the planning horizon subject to the technical and operational constraints. Also, to take the advantages of new technologies, the renewable and non-renewable distributed generations have been included in the problem as another alternative. The uncertainties related to renewable DGs, load demand, and energy price have been considered in the calculation of cost components. The load duration curve has been utilized for loads such that the results be more precise. The possibility of islanding and load transferring through the reserve feeders have been regarded in the problem to improve the reliability of the network. Also, the required condition for successful and safe operation of island considering all of uncertainty states have been checked out to accurately calculate the reliability. The genetic algorithm is employed to solve this integrated problem. Finally, the proposed method is applied to the 54-bus system and also a real large-scale distribution network, and the results are discussed. The results verify the effectiveness of the presented method.     

一种电力市场环境下的电源规划多智能体模型

电源规划一直是电力系统中重要问题之一。在电力市场环境下,这一问题更加复杂、迫切。针对这一问题,基于多智能体技术,提出了电力市场环境下发电集团电源投资规划模型。首先,构建了一个电力市场发电侧的双层优化架构,以实现市场竞价问题与电源规划问题相结合。其次,设计了发电集团、发电市场以及发电厂等智能体,并引入遗传算法、Q-learning算法完善各智能体寻优能力。通过算例验证了所建立的模型是可行的、有效的,可为电站建设决策部门提供有价值的参考。     

A Petri net based protection monitoring system for distribution networks with distributed generation

Connection of distributed generation (DG) essentially changes distribution network operation and creates a range of well-documented effects varying voltage levels and short circuit currents. Among others, DG can alter protection system operations in distribution networks, leading to failure of reclosing, disconnection of healthy feeder or prevention of protection operation. This paper proposes a procedure, based on Petri nets and supported by a centralized monitoring architecture for monitoring failures of the protection systems in radial distribution networks. Some case studies applied to a real Italian distribution network proved the effectiveness of the proposed procedure that can therefore represent an effective solution to improve distribution systems reliability in presence of DG.     

A technical evaluation framework for the connection of DG to the distribution network

Technical advances and institutional changes in the electric power industry have resulted in a constantly increasing penetration of distributed generation (DG) resources in the grids. For the connection of new DG installations to the network a variety of factors are taken into account, including technical requirements imposed by utilities to ensure that the DG station does not adversely affect the operation and safety of the network. In this paper, fundamental issues related to the interconnection of DG installations to the grid are discussed and evaluation rules are presented, which address power quality considerations and are suitable for application by electric utility and DG engineers. The attention is focused on the steady-state and fast voltage variations, flicker and harmonic emissions. The simplified evaluation procedures of the paper are largely based on the relevant IEC publications and reflect the current practice of several European utilities. A discussion of the interconnection protection requirements is also included in the paper.     

A procedure for distribution system planning of a large-scale agricultural project

Different mathematical techniques adapting linear, nonlinear, mixed-integer, and network flow programming have been developed over the past decades to solve the distribution planning optimization problem. The high dimensionality of the problem made it in some of practical cases unmanageable by such classical optimization techniques. This gave rise to the application of knowledge based, heuristics, artificial intelligence, and approximate iterative techniques to search for the optimal solution. The problem also was typically perceived from the distribution companies’ perspectives with the objective being to supply sustainable yet cost effective power to multi-objective multi-interest consumers with different damage functions and relatively uncertain data. This paper presents a value-based distribution system planning procedure for large-scale agricultural real life project. This type of distribution planning is characterized not only by high load demand but also with a huge distribution network covering the vast agricultural area. Yet it is a planning for single type of customers who has a consistent developing policy, interest, cost damage function, together with a realistic and less uncertain data. The planning is also perceived from the consumer perspective who may even question the connection to the power utility unless it is proved as cost effective way of power supply. Macro and micro-levels planning is suggested for both overall project and farm modules, respectively. The proposed planning procedure evaluates different feasible alternatives based on life cycle cost while reliability indices and cost of interruption are taken into consideration. The procedure is illustrated on the micro-level for a real life agricultural problem.     

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.     

分布式发电对配电网继电保护及自动化的影响

大量分布式发电的并网运行将深刻影响现有配电网络的结构、以及配电网中短路电流的大小、流向及分布,由此给配电网的运行与控制带来多方面的影响.针对基于断路器的三段式电流保护、基于重合器等自动化电器的馈线保护以及基于FTU的配网自动化保护方案,探讨了分布式发电对配电网继电保护以及自动化的影响.     

A novel algorithm for ATC calculations and applications in deregulated electricity markets

In this new deregulated environment, transmission networks should be regulated to ensure a competitive, open, and reliable market, which relies on the implementation of many transmission assessment functions. Among them, a key concept is the ability to quantify accurately and rapidly the capabilities of the transmission system. Accurate ATC values on major interfaces of the system can provide an important index to evaluate system security and reliability.

The main contribution of this paper is to propose a novel algorithm for contingency ATC computation and a sensitivity analysis for system uncertainties. It incorporates linear distribution factors and AC load flow sensitivity-based method in order to calculate ATC values efficiently and speedily considering line outages.     

Generation expansion planning in electricity markets: A novel framework based on dynamic stochastic MPEC

This paper presents a novel framework for generation expansion planning (GEP) of restructured power systems under uncertainty in a multi-period horizon, which includes generation investment from a price maker perspective. The investment problem is modeled as a bi-level optimization problem. The first level problem includes decisions related to investment in order to maximize total profit in the planning horizon. The second level problem consists of maximizing social welfare where the power market is cleared. Rival uncertainties on offering and investment are modeled using sets of scenarios. The bi-level optimization problem is then converted to a dynamic stochastic MPEC and represented as a mixed integer linear program (MILP) after linearization. The proposed framework is examined on a typical six-bus power network, MAZANDARAN regional electric company (MREC) transmission network as an area of IRAN interconnected power system and IEEE RTS 24-bus network. Simulation results confirm that the proposed framework can be a useful tool for analyzing the behavior of investments in electricity markets.     

新能源分布式发电系统储能电池综述

风、光等新能源分布式发电受天气和气候的影响出现间隙性和随机性等使得发电的不稳定缺点正成为阻碍其深度发展的重要障碍。储能技术的发展和应用,打破了风电、光伏发电等的接入和消纳瓶颈问题。介绍了应用于储能系统的主要化学储能电池:铅酸电池、液流电池、钠硫电池和锂电池的技术发展、组成结构和储能原理,详细对比了各种电池的性能及特点,特别对能量密度、功率密度和功率等级进行介绍,这是储能系统电池元件选择的关键,最后对储能电池的应用和发展作了展望。     

主动配电系统中分布式电源和储能系统的优化配置

针对多类型分布式电源和储能系统在主动配电系统中的接入位置及容量问题,建立了综合主动配电系统的经济成本、电压质量以及CO_2排放量三个方面的多目标优化配置模型。对传统的NSGA-Ⅱ算法进行了改进,在初始种群中引入反向学习机制,并以一定比例选择种群中的支配个体,以增加种群的多样性和提高算法的搜索能力,然后基于权重系数调节方法帕累托最优解集中确定最优解。最后,利用IEEE-33配电系统算例验证了所提出模型和算法的正确性和可行性。     

Short-term operation planning on cogeneration systems: A survey

This paper presents a survey of the developed researches from 1983 up to 2006 related to the cogeneration systems. The survey is focused on short-term operation planning and papers are grouped according to the most important characteristics. This paper contributes to: (i) give an extensive survey in the area and (ii) mention aspects in the short-term operation planning that have been poorly developed and where future contributions are required.     

含分布式电源的三相不平衡配电网潮流计算

根据配电网三相不平衡的实际情况,为准确计算各种分布式电源(distributed generation,DG)并入配电网后的潮流问题,文章基于前推回代法,提出了可处理PV和PQ节点模型DG的三相不平衡潮流算法。按照配电网拓扑结构,利用支路分层技术,加快了潮流计算速度。在处理PV节点模型DG时,将电压正序分量幅值作为电压调节参数,计算电压正序分量幅值和额定电压幅值差,得到PV节点的无功补偿量,将DG由PV节点运行模型转换为PQ节点运行模型。IEEE 34节点系统算例结果验证了该算法的正确性。最后,通过分析DG对电压的调节和无功补偿能力,研究了不同类型DG对配电网电压的影响。     

Voltage regulation in distribution networks in the presence of distributed generation: A voltage set-point reconfiguration approach

In this paper a control strategy based on predictive control ideas is proposed for reconfiguring on-line the on-load tap changer (OLTC) voltage set-point in electrical medium voltage (MV) power grids in the presence of distributed generation (DG). The idea is that an active management of the set-point can be effective for maintaining relevant system variables within prescribed operative constraints in response to unexpected adverse conditions, e.g. changing loads or generation failures. The voltage set-point reconfiguration problem is formulated as a constrained optimization problem by imposing that the voltages at certain nodes have, compatibly with all prescribed constraints and changed conditions, minimal deviations from their nominal values. Simulation results show that the proposed approach ensures, under certain conditions, feasible evolutions to the overall network whenever critical events occur.