Distributed generation placement for congestion management considering economic and financial issues

Congestion management is one of the most important functions of independent system operator (ISO) in the restructured power system. This paper presents two new methodologies for optimal sitting and sizing of distributed generations (DGs) in the restructured power systems for congestion management. The proposed methodologies are based upon locational marginal price (LMP) and congestion rent that forms a priority list of candidate buses to reduce the solution space. The proposed priority list facilitates the optimal placement as well as the level of output power of DGs. The proposed methods are implemented on the IEEE 14-bus and IEEE 57-bus test systems to illustrate their effectiveness. An economic consideration of DG placement and its operation is also studied. Simulation studies and results analysis show that the proposed methodologies are capable of finding the best location and optimal size for DGs, which can alleviate congestion in transmission systems.     

A proposal for investment recovery of FACTS devices in deregulated electricity markets

The paper presents a methodology to quantify the benefits, in terms of monetary values, of FACTS devices when used in deregulated electricity market for congestion management. The proposed methodology is used in the proposal for investment recovery of FACTS devices. Despite the long history of development and mature technology, the practical installations of FACTS devices are still limited. The main reasons for few installations are high investment cost and lack of viable measures to quantify the long list of benefits offered by FACTS device. In this respect, the methodology proposed in the paper provides a promising solution. The proposed methodology is based on establishing pricing schemes with and without FACTS devices using OPF formulation. The volume of market with FACTS devices and the increase in surplus due to them forms the basis of quantifying their benefits. The pricing scheme does not destroy the incentive effect in short run and also makes possible the provision of merchant FACTS. The proposed concept was tested and validated with TCSC in five-bus test system. Result shows that, when TCSC is used to relieve congestion in the system and the investment on TCSC can be recovered.     

基于TCSC的优化阻塞模型设计与应用研究

针对柔性交流输电装置控制线路潮流的特点,在传统OFF的基础上,将调整网络参数与经济调度方法相结合,研究了计及TCSC的优化阻塞调度模型。求解过程中,把TCSC对系统的调节作用表述成节点附加功率的形式,并将TCSC控制参数纳入变量空间内寻优。IEEE5系统的仿真结果验证了该方法的有效性。     

A new method for secured optimal power flow under normal and network contingencies via optimal location of TCSC

In the deregulated power industry, private power producers are increasing rapidly to meet the increase demand. The purpose of the transmission network is to pool power plants and load centers in order to supply the load at a required reliability, maximum efficiency and at lower cost. As power transfer increases, the power system becomes increasingly more difficult to operate and insecure with unscheduled power flows and higher losses. FACTS devices such as Thyristor Controlled Series Compensator (TCSC) can be very effective to power system security. Proper location of TCSC plays key role in optimal power flow solution and enhancement of system performance without violating the security of the system. This paper applied min cut algorithm to select proper location of TCSC for secured optimal power flow under normal and contingencies operating condition. Proposed method requires a two-step approach. First, the optimal location of the TCSC in the network must be ascertained by min cut algorithm and then, the optimal power flow (OPF) with TCSC under normal and contingencies operating condition is solved. The proposed method was tested and validated for locating TCSC in Six bus, IEEE 14-, IEEE-30 and IEEE-118 bus test systems. Results show that the proposed method is good to select proper location of TCSC for secured OPF.     

Optimal power flow with FACTS devices by hybrid TS/SA approach

In this paper, a hybrid tabu search and simulated annealing (TS/SA) approach is proposed to minimize the generator fuel cost in optimal power flow (OPF) control with flexible AC transmission systems (FACTS) devices. The problem is decomposed into the optimal setting of FACTS parameters subproblem that is searched by the hybrid TS/SA approach and the OPF with fixed FACTS parameters subproblem that is solved by the quadratic programming (QP). Two types of FACTS devices are used: thyristor-controlled series capacitor (TCSC) and thyristor-controlled phase shifting (TCPS). Test results on the modified IEEE 30 bus system indicates that the proposed hybrid TS/SA approach can obtain better solutions and require less CPU times than genetic algorithm (GA), SA, or TS alone.     

Genetic algorithm-based fuzzy multi-objective approach to congestion management using FACTS devices

This paper investigates a novel optimization-based methodology for placement of Flexible AC Transmission Systems (FACTS) devices in order to avoid congestion in the transmission lines while increasing static security margin and voltage profile of a given power system. The optimizations are carried out on the basis of location, size, and number of FACTS devices. Thyristor Controlled Series Compensator (TCSC) and Static Var Compensator (SVC) are two FACTS devices which are implemented in this investigation to achieve the determined objectives. The problem is formulated according to Sequential Quadratic Programming (SQP) problem in the first stage to accurately evaluate static security margin with congestion alleviation constraint in the presence of FACTS devices and estimated annual load profile. In the next stage a Genetic Algorithm (GA)-based fuzzy multi-objective optimization approach is used to find the best trade-off between conflicting objectives. The IEEE 14-bus test system is selected to validate the proposed approach.     

Optimal DG placement in deregulated electricity market

This paper presents two new methodologies for optimal placement of distributed generation (DG) in an optimal power flow (OPF) based wholesale electricity market. DG is assumed to participate in real time wholesale electricity market. The problem of optimal placement, including size, is formulated for two different objectives, namely, social welfare maximization and profit maximization. The candidate locations for DG placement are identified on the basis of locational marginal price (LMP). Obtained as lagrangian multiplier associated with active power flow equation for each node, LMP gives the short run marginal cost (SRMC) of electricity. Consumer payment, evaluated as a product of LMP and load at each load bus, is proposed as another ranking to identify candidate nodes for DG placement. The proposed rankings bridges engineering aspects of system operation and economic aspects of market operation and act as good indicators for the placement of DG, especially in a market environment. In order to provide a scenario of variety of DGs available in the market, several cost characteristics are assumed. For each DG cost characteristic, an optimal placement and size is identified for each of the objectives. The proposed methodology is tested in a modified IEEE 14 bus test system.     

基于贡献因子理论的阻塞费用连续积分分摊方法

阻塞费用分摊是阻塞管理的重要内容之一.目前的基于AUMANN-SHAPLEY值的分摊方法需采用近似的离散数值积分方法,需多次求解系统最优潮流,不利于大系统应用.该文分析了DC潮流约束下阻塞消除过程中最优解及其灵敏度的变化规律,提出了基于贡献因子理论的阻塞费用简捷分摊方法.与现有方法相比,该文方法的显著特点是:阻塞费用分摊可采用连续积分方法,而不是近似的离散数值积分方法.交流潮流约束下也可采用文中方法.     

含TCSC的电力系统最优潮流控制

电力系统最优潮流问题(OPF)对保证系统的电压质量、安全性和经济性都是十分重要的。针对含有柔性交流输电系统的最优潮流问题,根据可控串联补偿器(TCSC)的功率注入模型,建立适于潮流和最优潮流计算的数学模型,在常规最优潮流问题的基础上,充分考虑TCSC元件对系统潮流的影响,从而建立起TCSC运行情况下的非线性最优潮流模型,并应用了一种有效的求解上述模型的方法——路径跟踪内点法。仿真表明该方法能有效解决含TCSC的电力系统最优潮流问题。     

基于TCSC技术和粒子群优化算法的电力系统阻塞疏导方法

提出了一种基于晶闸管控制的串连电容器(thyristor controlled series capacitor,TCSC)技术和粒子群优化算法的电力系统阻塞疏导方法。首先根据线路灵敏度分析确定安装TCSC的线路;然后提出了电力市场环境下电网中含有TCSC装置的阻塞疏导计算数学模型;最后运用粒子群优化算法对这一数学模型进行参数优化,达到疏导电网阻塞的目的。IEEE 14节点系统算例表明,基于TCSC技术进行电网阻塞疏导是有效、合理的。     

基于非线性内点方法的含有串联柔性输电系统装置的阻塞调度

提出了一种基于非线性内点方法的含有串联FACTS装置的阻塞调度方法。针对调节线路有功潮流问题选取了串联FACTS装置的控制参数和模型，并把FACTS对系统的调节作用表述成附加功率的形式。不引入FACTS的控制目标方程，而是在包含FACTS控制参数的变量空间内进行寻优，可以考虑FACTS的多种调节方式。该方法具有较好的鲁棒性和收敛性，易于利用原有的潮流优化算法和程序。     

考虑FACTS配置的电网输电能力计算

灵活交流输电(FACTS)技术是提高电网输电能力的有效手段。文章基于连续潮流法,将静止无功补偿器(static var compensator,SVC)和可控串联补偿器(thyristor controlled series capacitor,TCSC)的稳态模型加入潮流方程中,建立了计及SVC和TCSC的可用输电能力计算模型。考虑到确定元件安装位置的重要性,利用连续潮流法求取系统极限功率点的输电能力,以该值与网络参数的灵敏度系数作为指标,选择最有利于提高输电能力的SVC和TCSC安装位置。对IEEE 30和IEEE 118节点系统进行的仿真计算证明了所提出模型和方法的有效性。     

Assessment of techno-economic contribution of FACTS devices to power system operation

In contemporary power system studies, the optimal allocation and utilization of Flexible AC Transmission System (FACTS) devices are important issues primarily due to their cost. In this study four types of FACTS devices (Static VAr compensator (SVC), Thyristor-Controlled Series Capacitor (TCSC), Thyristor-Controlled Voltage Regulator (TCVR), and Thyristor-Controlled Phase Shifting Transformer (TCPST)) are optimally placed in a multi-machine power system to reduce the overall costs of power generation. The placement methodology considers simultaneously the cost of generated active and reactive powers and cost of selected FACTS devices for a range of operating conditions. The optimal power flow (OPF) and genetic algorithm (GA) based optimization procedure are employed to solve the allocation task. The net present value (NPV) method is used to assess the economic value of the proposed methodology. In addition to net reduction in generation cost allocated FACTS devices increased power transfer across the network and improved damping of electromechanical oscillations.     

Steady-state optimization in power systems with series FACTS devices

This paper presents an optimization-based methodology to identify key locations in the AC network where placement of a series-connected FACTS device increases the maximum megawatt power transfer the most. The models used for the thyristor-controlled series capacitor (TCSC) and unified power-flow controller (UPFC) include the nonlinear constraints of voltage limitation, zero megawatt active-power exchange, voltage control, and reactive-power exchange. This article describes briefly the steady-state flexible AC transmission systems (FACTS) models and their integration in an existing optimal power-flow (OPF) software package designed and implemented by the authors. A reduced real-life network is used for the case studies. The optimization results help in evaluating the effectiveness of the series FACTS devices in maximizing the network transfer capability and deliver a measure of the FACTS ratings.     

Modeling of the generalized unified power flow controller (GUPFC)in a nonlinear interior point OPF

With the progress of installing the latest generation of FACTS devices, namely, the convertible static compensator (CSC), several innovative operating concepts have been introduced to the historic development and application of FACTS. One of the novel concepts is the generalized unified power flow controller (GUPFC) or multi-line UPFC, which can control bus voltage and power flows of more than one line or even a sub-network. The GUPFC should have stronger control capability than the UPFC. A mathematical model for the GUPFC consisting of one shunt converter and two or more series converters is developed and implemented in a nonlinear interior point OPF algorithm. Numerical results with various GUPFC devices based on the IEEE 30 bus system and IEEE 118 bus system demonstrate the feasibility as well as the effectiveness of the GUPFC model established and the OPF method proposed     

含广义统一潮流控制器(GUPFC)的最优潮流模型和算法研究

广义统一潮流控制器(GUPFC)作为比统一潮流控制器(UPFC)控制能力更强大的FACTS装置，其对最优潮流(Optimal Power Flow)的影响需要深入地研究。根据GUPFC的控制原理，基于功率注入法建立了含GUPFC的OPF数学模型，并采用基于信赖域内点法的最优潮流算法予以求解。该算法采用多步中心校正原一对偶内点法连续求解线性规划子问题，通过信赖域决定线性化步长的选取。对IEEE30和118节点系统作了数值计算，结果表明，GUPFC不仅可控制节点电压而且可控制多条线路潮流，显示出强大的控制能力，同时也说明了含GUPFC的OPF数学模型和算法的可行性和有效性。     

计及负荷静态电压特性的实时定价方法

提出了一种基于最优潮流且计及负荷静态电压特性的实时定价模型并讨论了负荷模型对交易的影响。采用原–对偶路径内点法对模型进行求解,因为特定的负荷模型对应着最优潮流计算中特定的雅可比矩阵的结构和信息,所以负荷模型对节点边际电价、节点阻塞电价及市场利益分配结果均有重要影响,基于K-T一阶最优性条件定义了能够综合评估负荷需求、报价和负荷静态电压特性对交易产生影响的灵敏度指标。IEEE30节点算例表明了本文所提出的模型和指标的可行性和合理性。     

阻塞管理和电压安全

电力市场下的阻塞管理与系统电压安全密切相关。采用将最优潮流与连续潮流相结合的方法解决阻塞问题,并使系统运行在电压安全裕度之内。提出两种算法结合迭代求解流程．并用步长函数描述连续潮流法CPF(Continuation Power Flow)中的步长选择过程。IEEE-30节点和IEEE-57节点系统的结果表明,所提方法可避免或减轻网络阻塞,且不危及系统的电压安全裕度。     

选择最佳TCSC安装地点提高电力系统电压稳定性

选择最佳的FACTS安装地点以提高电力系统的电压稳定性是一个重要而又实际的问题。负荷裕度是一种被一致认可的基本的电压稳定指标，文中推导了负荷裕度对线路电抗的灵敏度，该灵敏度可以被用来衡量在不同线路上装设TCSC提高电压稳定性的效用，文中以此为指标选择最佳TCSC的安装地点。该方法对系统的模型没有特殊要求，因而诸如负荷电压特性之类对电压稳定影响较大的因素可被考虑在内，从而提高了结果的准确性和实用性。最后在IEEE 14节点系统中应用该方法，证明了所提方法是有效的。     

Congestion Management Considering Optimal Placement of Distributed Generator in Deregulated Power System Networks

This article presents an effective methodology for congestion management in deregulated power system networks considering optimal placement of a distributed generator. The novelty of this method is that the optimal placement of a distributed generator in a deregulated power system is decided on the basis of bus impedance matrix (Z_bus ) based contribution factors. The Z_bus -based contribution factors are independent of slack bus location, which complies with the prevailing competitive environment. The congestion management problem formulation comprises the maximization of social welfare function subject to power balance and transmission congestion constraints. The maximization of the social welfare function causes maximization of consumer benefits and minimization of supplier generation cost and distributed generators. The proposed methodology has been simulated on an IEEE 30-bus system, and comparisons of results are presented with and without distributed generators. The results show that the proposed approach gives significant improvement in social welfare and decreases congestion rent with distributed generator placement.