Planning of multi-type FACTS devices in restructured power systems with wind generation

Many electrical power systems are changing from a vertically integrated entity to a deregulated, open-market environment. This paper proposes an approach to optimally allocate multi-type flexible AC transmission system (FACTS) devices in restructured power systems with wind generation. The objective of the approach is to maximize the present value of long-term profit. Many factors like load variation, wind generation variation, generator capacity limit, line flow limit, voltage regulation, dispatchable load limits, generation rescheduling cost, load shedding cost, and multilateral power contracts are considered in problem formulation. The proposed method accurately evaluates the annual costs and benefits obtainable by FACTS devices in formulating the large-scale optimization problem under both normal condition and possible contingencies. The overall problem is solved using both Particle Swarm Optimization (PSO) for attaining optimal FACTS devices allocation as main problem and optimal power flow as sub optimization problem. The efficacy of the proposed approach is demonstrated for modified IEEE 14-bus test system and IEEE 118-bus test system.     

Application of Multi-Objective Evolutionary Optimization Algorithms to Reactive Power Planning Problem

This paper presents a new approach to treat reactive power (VAr) planning problem using multi-objective evolutionary algorithms (EAs). Specifically, strength Pareto EA (SPEA) and multi-objective particle swarm optimization (MOPSO) approaches have been developed and successfully applied. The overall problem is formulated as a nonlinear constrained multi-objective optimization problem. Minimizing the total incurred cost of the VAr planning problem and maximizing the amount of available transfer capability (ATC) are defined as the main objective functions. The aim is to find the optimal allocation of VAr devices in such a way that investment and operating costs are minimized and at the same time the amount of ATC is maximized. The proposed approaches have been successfully tested on IEEE 14 buses system. As a result a wide set of optimal solutions known as Pareto set is obtained and encouraging results show the superiority of the proposed approaches and confirm their potential to solve such a large-scale multi-objective optimization problem. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于状态变化的无功补偿装置的最优配置

以弱节点作为无功补偿装置的最佳配置地点,提出了一种基于过渡状态的无功补偿装置最优配置问题的改进数学模型。该模型同以往模型的不同之处在于对安全性问题的考虑,直接将电压崩溃和恢复控制以费用函数来表示,并体现在目标函数中。求解该模型是一个混合整数非线性规划问题,采用多种群遗传算法来进行优化,避免了采用Benders 分解带来的解的发散问题。对AEP14节点系统的计算结果表明,文中的优化方法具有较强的工程实用性。     

大规模风电接入下输电网扩展规划的启发式优化算法

提出了大规模风电接入下的输电网有功和无功扩展规划的解决方法。计及了风电与负荷的全年时序数据,并将网络设备投资的年值成本与方案在全年所有不满足安全约束场景下采取控制措施的成本之和最小作为规划目标。为了降低求解计算的复杂性,将原问题分解为网络设备投资决策与方案的控制措施成本评估2个子问题,二者借助原问题的规划目标进行总体协调。在此基础上,通过分析规划目标与问题本身的特性,设计了启发式的优化算法,明显地提高了计算速度。算例分析验证了所提方法的正确性和求解算法的有效性。     

A new Optimal reactive power planning based on Differential Search Algorithm

This paper proposes a new multi-level methodology based on the optimal reactive power planning. The developed methodology is designed to solve the problem of the non-feasibility solution of the fuel cost minimization problem (for a given operating point) where the classical method such as interior point method (IPM) is applied. The proposed solution to solve this problem is based on the application of the optimal reactive power planning problem considering voltage stability as the initial solution of the fuel cost minimization problem. To improve the latter the load voltage deviation problem is applied to improve the system voltage profile. For à good result improvement, the reactive power planning problem and the load voltage deviation minimization problems are solved using a new optimization method namely the Differential Search Algorithm (DSA). Moreover, the fuel cost minimization problem is solved using IPM. To identify the candidate placements of compensation devices for the optimal reactive power planning problem, a new voltage stability index namely: The Fast Voltage Stability Index (FVSI) is used. The methodology has been tested with the equivalent Algerian power system network, and the simulation results show the effectiveness of the proposed approach to improve the reactive power planning problem and to minimize the system voltage deviation.     

A new methodology for the provision of reserve in an isolated powersystem

New operating and planning policies are emerging in power utilities throughout the world with the onset of competition and deregulation. These new policies fundamentally differ from those previously implemented. In particular, the approach adopted to power system security is significantly different. Previously, power systems were operated to ensure a certain level of security was maintained at all times. In the new competitive markets, the balance between cost and security is a dominant factor. To illustrate this, a new economic dispatch methodology is proposed for a small isolated power system. This methodology enables the cost of providing sufficient reserves to just avoid load shedding following the loss of any given unit to be calculated and assessed against the risk and cost of load shedding. An illustrative test case is examined in this paper which considers the loss of the three largest units. The dispatch costs are calculated and compared to the cost and probability of load shedding to create a schedule consistent with the new utility policies     

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.     

Dynamic security constrained optimal power flow/VAr planning

Traditionally security constrained optimal power flow and VAr planning methods consider static security observing voltage profile and flow constraints under normal and post contingency conditions. Ideally, these formulations should be extended to consider dynamic security. This paper reports on a BC Hydro/CEPEL joint effort establishing a dynamic security constrained OPF/VAr planning tool which considers simultaneously static constraints as well as voltage stability constraints. This paper covers the details of formulation and implementation of the tool together with the test results on a large scale North American utility system and a reduced Brazilian system     

计及可靠性的电-气-热能量枢纽配置与运行优化

含可再生能源的电—气—热互联多能源系统可实现多能源网络互联与多能源优化利用,有效解决资源匮乏与能源浪费等问题。能量枢纽是多能源耦合的关键,但现有的能量枢纽优化配置问题未考虑系统运行可靠性的影响。因此,重点研究多能源系统中计及可靠性的能量枢纽优化配置问题。首先,针对风机、变压器、热电联产、燃气锅炉、电储能、热储能等设备组成的能量枢纽,建立了一种新型多能源系统容量协同优化配置的混合整数线性规划模型。然后,根据该双层优化模型计及能量枢纽的运行可靠性,引入失负荷期望等可靠性指标作为约束。最后,为了确定配置方案,结合优化策略进行整体规划,同时得到各机组能量分配情况,对算例进行仿真分析。结果表明,提出的模型有利于负荷供应可靠性的提升。     

Determination of load shedding to provide voltage stability

A computationally simple algorithm is developed for studying the load shedding problem in emergencies where an ac power flow solution cannot be found for the stressed system. The proposed algorithm is divided into two sub-problems: restoring solvability sub-problem and improving voltage stability margin (VSM) sub-problem. Linear optimization (LP)-based optimal power flow (OPF) is applied to solve each sub-problem. In restoring solvability sub-problem, rather than taking restoring power flow solvability as direct objective function, the objective function of maximization of voltage magnitudes of weak buses is employed. In VSM sub-problem, the traditional load shedding objective is extended to incorporate both technical and economic effects of load shedding and the linearized VSM constraint was added into the LP-based OPF. Case studies with a real 682 bus system are presented. The simulation results show that the proposed load shedding algorithm is effective, fast in finding the load shedding scheme to solve the problem of restoring solvability and improving VSM.     

Voltage security enhancement via coordinated control

The problem of analytically coordinating dissimilar voltage control actions to prevent voltage collapse in a large power system is addressed. A framework for hybrid voltage control based on coordination of controls with different response time and dynamic characteristics is presented. The proposed method is based on a security constrained steady-state approach. The minimum distance from the operating point to the bifurcation boundary is used to evaluate system voltage security. The optimal control direction toward adequate security is then obtained by calculating the sensitivity of the minimum distance with respect to control parameters. The actual dispatch of controls along the optimal direction, which takes into account impacts of economic cost and control availability, is determined as the solution of a multiple-stage optimization problem using differential dynamic programming. The algorithm is demonstrated for a system with dynamic load models representing the main grid of New South Wales, Australia     

Static security in power system operation with fuzzy real loadconditions

This paper presents a mathematical formulation for optimal power flow (OPF) taking into account the fuzzy modeling of static power system security constraints due to the uncertainty in bus loads. Uncertainties in MW loads and generations are translated into possibility distribution functions. The fuzzy OPF problem is decomposed, via Dantzig-Wolfe decomposition, into subproblems corresponding to the possibility distributions of loads. The effects of phase shifters are modeled as equivalent real power injections at corresponding system buses, which preserves the Y-bus symmetry and maintains minimum memory requirements. Contingency constraints are added to the fuzzy OPF problem. Fuzzy sets are utilized to exercise a tighter control on least cost real power generation with minimum emission dispatch solution. The final solution is a compromise among cost, static security and emission considerations. Numerical results for the application of the proposed approach to test systems are discussed     

考虑直流系统双极闭锁故障的受端电网运行成本优化

现有的电力系统运行优化大多没有考虑故障短期运行安全约束,导致其优化结果没有为故障短期内快速控制保留充分有功备用,尤其在含特高压直流输入的电力系统发生直流闭锁故障后将会出现大量有功缺额,从而导致故障后系统大面积切负荷,给电力系统带来了严重经济损失。提出了一种考虑故障短期运行安全约束的含特高压接入受端系统发输电运行优化模型。首先,在含特高压接入受端系统中设置含直流双极闭锁在内的多个N-1故障。其次,在传统N-1安全约束下最优潮流规划模型中加入故障短期安全约束。最后,以发输电成本最小和切负荷成本最小为目标函数,提出了含特高压接入的受端电网运行成本优化模型。该模型在修改后的IEEE39节点系统中得到验证。     

Simulation of load shedding as a corrective action against voltage collapse

The evolution of a lot voltage collapse scenarios on large power systems can be alleviated by controlled load shedding associated with rearrangement of generator outputs. Dynamic simulation of power system mid-term voltage response is required to adequately determine the impact of load shedding actions and to design appropriate control systems. The dynamic simulation must take into account load-voltage behaviour, transformer tap changer controls and limits, generator overexcitation limiters, automatic generation control and system protective devices. This paper demonstrates the impact of load shedding as a corrective action through simulation of the system dynamic response to a disturbance. Whilst load shedding can stabilise a system, rigorous techniques are required to identify the magnitude and location of shedding. The application of voltage modal analysis in combination with the determination of reactive power margins in resolving this problem is demonstrated.     

基于SCUC的可入网混合电动汽车优化调度方法

在可入网混合电动汽车(PHEV)有望规模化应用的背景下,以传统的计及安全约束的机组最优组合(SCUC)问题为基础,发展了能够容纳PHEV的电力系统优化调度数学模型。所发展的模型以保证系统安全运行为前提,兼顾了PHEV车主的经济效益与发电的碳排放成本。利用PHEV作为可移动电量储存单元的特性,将模型解耦为机组最优组合与计及交流潮流约束的充/放电计划优化2个子模型。应用混合整数规划方法和牛顿—拉夫逊潮流算法迭代求解优化问题,可以同时获取日前机组调度计划和各时段的PHEV最优接纳容量及充/放电计划等结果。最后,以6节点和IEEE 118节点2个系统为例,验证了所构建模型的正确性和有效性。     

考虑风电和负荷不确定性的输电网多目标柔性规划

风电大规模集中并网使输电网中电源出力的不确定性显著增强,并且当前考虑风电和负荷不确定性的输电网规划模型大多采用直流潮流,规划结果的准确性有待提高.以交流潮流为基础,构建了考虑风电和负荷不确定性的输电网多目标柔性规划双层模型.上层模型是以建设投资等年值费用、年网损费用和运行效率为目标的输电网多目标规划模型,采用带精英策略...     

A wide area synchrophasor-based load shedding scheme to prevent voltage collapse

This paper presents a new method based on wide area voltage stability index for optimal load shedding to prevent voltage instability phenomena. Phasor Measurement Units (PMUs) have widely been used in recent years due to their great advantages in power systems wide area monitoring, protection and control. The purpose of this paper is to provide a new optimal load shedding method, which disconnects the least possible amount of load from optimum buses. Not only the system stability is considered as main goal in this research, but also minimum load shedding is taken into account. Moreover, the problem of optimal load shedding is applied using modified Discrete Imperialistic Competition Algorithm (DICA) in mid-term and long-term voltage instability scenarios. In all investigations, certain limitations are considered to obtain practical answers. In addition, some modifications are applied to the conventional ICA, which make it proper for solving the optimal load shedding problem. New modifications result in fast convergence characteristic and less run time, which are crucial in dealing with power system instability problems.     

区间负荷下的输电网灵活规划方法

建立了区间负荷下的输电网灵活规划模型,该模型考虑负荷的不确定因素,以投资成本最小为目标,以正常情况和线路N-1情况下的网络安全为约束,求解该模型得到区间负荷下满足正常情况和线路N-1情况下系统安全的输电网规划方案。根据区间至多切负荷量的数值来判别区间负荷下电网规划方案的安全性和安全程度,使用改进的贪婪随机自适应搜索算法快速求解该模型。6节点系统和某实际77节点系统的规划结果验证了该方法的正确性和有效性。     

A heuristic and algorithmic approach to VAR planning

The authors present a knowledge- and algorithm-based approach to voltampere-reactive (VAr) planning in a transmission system. The VAr planning problem involves the determination of locations and sizes of new compensators considering contingencies and voltage collapse problems in a power system. An expert system model analyzes the operating conditions of a power system and suggests one or more of the P-V, Q-V and S-V (S denotes the system complex power) curves for use in assessing the voltage collapse problem. A second expert system module suggests control actions with the existing VAr controllers and sizes and locations for the installation of new compensators. The IEEE 30-bus system was used to demonstrate the capability of the proposed approach     

含新型统一潮流控制器的电力系统安全校正模型

统一潮流控制器(UPFC)串联侧和并联侧接于不同母线的新型拓扑使得UPFC的传统稳态模型难以适用,灵敏度类安全校正方法忽略了无功功率的影响,可能会引入新的不安全因素。基于此,提出一种适应性更强的UPFC稳态模型,并提出一种含UPFC的潮流计算优化模型。在考虑无功功率的影响后,引入0-1变量将安全校正问题转化为以调整设备数目最少和调整量最少为目标的多目标优化问题。然后,通过权重区分发电机节点和负荷节点,减少切负荷动作的发生。最后,利用极大值法将多目标优化问题转化为单目标优化问题,降低模型求解难度。116节点实际等值系统的算例测试表明,所述安全校正模型可利用最少的调整设备和调整量,消除系统过载故障。UPFC参与调控可提高系统安全校正效率。