Power injection modeling and optimal multiplier power flow algorithm for steady-state studies of unified power flow controllers

This paper presents an optimal multiplier based Newton-Raphson power flow algorithm for reliably and efficiently handling power systems with embedded flexible AC transmission systems (FACTS) devices such as unified power flow controllers (UPFCs). A power injection transformation of a two voltage source UPFC model is derived in rectangular form. After detailed analyses of issues in implementation of UPFCs in power flow programmes by various power flow algorithms, the optimal multiplier power flow method for ill-conditioned systems is adopted. The proposed UPFC model and power flow algorithm have been programmed and vigorously tested in a number of systems. The results on the IEEE 30-bus test system and a 306-bus practical system are reported and compared with conventional user defined model type programmes, which clearly illustrate the effectiveness of the proposed algorithm.     

Considering system non-linearity in transmission pricing

In this paper a new approach for transmission pricing is presented. The contribution of a contract on power flow of a transmission line is used as extent-of-use criterion for transmission pricing. In order to determine the contribution of each contract on power flow of each transmission line, first the contribution of each contract on each voltage angle is determined, which is called voltage angle decomposition. To this end, DC power flow is used to compute a primary solution for voltage angle decomposition. To consider the impacts of system non-linearity on voltage angle decomposition, a method is presented to determine the share of different terms of sine argument in sine value. Then the primary solution is corrected in different iterations of decoupled Newton–Raphson power flow using the presented sharing method. The presented approach is applied to a 4-bus test system and IEEE 30-bus test system and the results are analyzed.     

基于矢量化运算模式的电力系统潮流计算

通过把电力系统潮流方程的求解转化为一个新的非线性规划模型的求解,解决了病态系统潮流计算发散的问题,为给定条件下的潮流计算是否有解提供了一个新的判断途径。利用牛顿法获得具有对称不定系数矩阵的修正方程后,采用AMD算法对系数矩阵进行排序,并采用LDLT算法进行求解,提高了修正方程的求解速度。整个潮流计算模型以矢量化形式表达,简化了程序复杂度,提高了代码的通用性和易维护性。对节点数从118到703共3个测试系统进行了仿真计算,结果验证了文中所提方法的正确性。     

Transmission losses based MW contingency ranking

Contingency ranking and selection is an indispensable tool for static security analysis. Several performance indices suffer either from misranking or computational inefficiencies. This paper presents a new performance index for MW line flow contingency selection and ranking. The proposed index is derived from real power transmission losses. It is a quadratic function of bus voltage angles and can easily be calculated from real power flows or DC load flow. It improves both the selectivity and the ranking of second order performance index without excessive computational effort. The proposed method is tested on IEEE 24-bus reliability test system and IEEE 30-bus test system. The results are compared with those of the conventional second order performance index and of the tenth order reference performance index from the point of ranking and selectivity.     

基于目标级联分析法的输电网结构优化

为了充分利用可再生能源,增强电力系统各区域间的互联协调能力,提出了一种基于目标级联分析(ATC)法的输电网结构优化模型。首先,利用母线撕裂法将电力系统解耦为多区域互联系统;其次,建立含可再生能源发电的输电网结构优化模型,在此基础上,进行多区域互联电力系统的统一分析和决策;再次,采用ATC法将模型分解为主问题和子问题进行并行计算,实现源网荷协同的输电网结构优化。最后,通过对IEEE 14节点及IEEE 118节点系统的测试分析,验证了所提模型可有效协调互联电网的运行,提高电力系统运行的经济性。     

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.     

全局输配电网电压稳定故障筛选与排序的分布式计算方法

随着传统配电网向含大量分布式电源的主动配电网转变,输电网、配电网电压稳定评估已不再适宜各自独立计算。基于输电网、配电网分属于不同控制中心调控,提出一种全局输配电网电压稳定故障筛选与排序的分布式计算方法。该方法分为两阶段：阶段1中采用输配电网主从分裂分布式潮流工具在系统要求最小负荷裕度值的工况下进行各预想故障的潮流计算,采用最优乘子法筛选出潮流不可解的严重故障;阶段2中采用基于输配电网分布式连续潮流的步长加速二次曲线拟合方法计算严重故障的负荷裕度并进行排序。由1个IEEE 118节点输电网和2个IEEE 33节点配电网组成的全局输配系统的仿真算例表明所提方法能够快速可靠地实现全局输配电网电压稳定故障筛选与排序。     

交直流输电系统潮流计算中换流器运行方式的转换策略

分析了多端直流输电系统和多馈入直流输电系统控制运行方式，提出了采用计算机进行控制方式转换的方法。在考虑各种控制方式的控制作用和转换条件的基础上计算交直流系统潮流。该方法用加入2条直流输电线路的IEEE 300节点算例系统和加入三端直流输电系统的IEEE 118节点算例系统进行测试，计算效果较好，能够处理运行条件改变导致的运行方式发生的转换。     

Optimization of Transmission Expansion Planning by Minimal Cut Sets Based on Graph Theory

Abstract—This research proposes a method based on the graph theory for transmission network expansion planning. The proposed method suggests an optimal investment cost for transmission network expansion planning by using the minimal cut sets based on the graph theory. On the basis of the oriented connected graph of an intent transmission network, this research aims to find the maximum power flows through the bottlenecks of the network. The main object function of the proposed algorithm is the construction cost of new lines, which needs to be added in parallel with the overloading lines of an existing transmission network. The major consideration is the load demand in the given future. This research uses three benchmark systems to illustrate the proposed method: Garver's 6-bus system (Garver system) the 24-bus and 21-bus IEEE reliability test systems. In a word, the Garver system is used to demonstrate the algorithm of the proposed method, and the 24-bus and 21-bus IEEE reliability test systems are tested by using the proposed method in many cases to compare the results and performance with those of recent studies. The findings of this research are of value to solve transmission network expansion planning problems.     

一种基于潮流追踪的电力系统无功补偿方法

提出了一种旨在改善电力系统无功传输和降低有功网损的无功补偿点选择和补偿容量确定方法。该方法通过无功潮流追踪,获得负荷无功功率的传输路径,结合无功流动与支路有功网损的关系,定义了节点的网损分摊系数,进而根据系数的大小选择无功补偿点;推导了网损分摊系数对负荷无功功率的近似表达式,结合网损优化的近似模型,推导出了各补偿点最优补偿容量的计算公式;通过39节点测试系统,验证了该方法的有效性。所提出的网损分摊系数的物理概念清晰,计算便捷,据此进行的无功补偿对改善无功分布和降低网损均有较好的效果。     

Optimal Location of Thyristor-controlled Series Capacitor to Enhance Power Transfer Capability Using Firefly Algorithm

Abstract—The optimal power flow problem seeks to find an optimal profile of active and reactive power generations along with voltage magnitudes in such a manner as to minimize the total operating costs of a power system while satisfying network security constraints. This article presents a firefly algorithm to solve the optimal power flow problem incorporating a thyristor-controlled series capacitor. A thyristor-controlled series capacitor is considered to find the optimal location in transmission lines to enhance the power transfer capability of the transmission line. To assess the effectiveness of the proposed algorithm, it was tested on a 5-bus test system, an IEEE 14-bus system, and a modified IEEE 30-bus system, and it was compared with the genetic algorithm and differential evolution with and without a thyristor-controlled series capacitor. It has also been observed that the proposed algorithm can be applied to larger systems and does not suffer with computational difficulties. The results show that the firefly algorithm produces better results than others and has fast computing time for solving the optimal power flow problem with a thyristor-controlled series capacitor.     

Optimal power flow solution of two-terminal HVDC systems using genetic algorithm

The usage extensively of high voltage direct current (HVDC) transmission links in recent years makes it necessary further work in this area. Therefore, two-terminal HVDC transmission link is one of most important elements in electrical power systems. HVDC link representation is mostly ignored and simplified for optimal power flow (OPF) studies in power systems. OPF problem of purely alternating current (AC) power systems is defined as minimization of the fuel cost to subjected equality and inequality constraints. Hence, OPF software of purely AC power systems is extended by taking into consideration power transfer control characteristics of HVDC links. In this paper, OPF problem of integrated AC–DC power systems is first solved by genetic algorithm that is a heuristic algorithm based on evolutionary. The proposed method is tested on two test systems which are the modified 5-node test system and the modified WSCC 9-bus test system. In order to show effectiveness and efficiency of the proposed method, the obtained results are compared to that reported in the literature.     

混合输电权设计及其内点法实现

基于交流最优潮流模型，提出了混合输电权概念，包括点对点的输电权和关口输电权组合，建立了实现该输电权拍卖的模型。利用非线性内点法形成新的线性迭代系统保持了原有最优潮流中的对称性及稀疏结构，通过对原有最优潮流进行少量修改即可实现该输电权的拍卖计算。IEEE 9节点算例证明了文中所提方法的有效性，对交流潮流模型下实现输电权拍卖计算进行了有益的探索和尝试。     

计及不确定性的电力系统直流潮流的区间算法

考虑高压输电网络中的不确定性因素，采用区间分析方法来处理直流潮流计算中的不确定问题，提出了一种可应用于求解大规模输电系统的区间直流潮流算法。该算法考虑了节点注入有功功率的不确定性，采用区间高斯消去法求解区间线性方程组，得到母线电压相角和支路有功功率的上下限，即区间潮流方程的区间解。采用IEEE 30算例系统，将该算法的计算结果与蒙特卡罗仿真计算的结果相比较，验证了该算法的有效性和应用价值。     

A bi-level probabilistic transmission planning with intermittent generations based on life cycle cost

With the growing development of intermittent renewable energy sources, such as wind and solar, transmission planners are faced with uncertainly varying generations and resultant probabilistic power flow. A bi-level programming model is proposed to coordinate the process of decision making and reliability assessment. Based on the concept of life cycle cost (LCC), its minimization can be defined as the objective function of a transmission planner. This upper level problem needs to be solved jointly with the lower probabilistic optimal power flow problem of minimizing the load shedding in the system. Hence the bi-level problem is transformed into a Mathematical Programming with Equilibrium Constraints (MPEC) with Karush-Kuhn-Tucker conditions. Due to the nonlinearity nature of MPEC, disjunctive inequalities and Generalized Benders Decomposition methods are used to solve this problem. Results of both Garver’s 6-bus test system and a realistic 63-bus system are used to illustrate the rationality and validity of the proposed method.     

计及拓扑结构和运行状态的支路重要度评估方法

准确快速地识别出关键支路,对于提高电网运行的稳定性及防止大停电事故的发生具有重要意义。文中将复杂网络理论和熵理论有机结合,从结构和状态两个角度对支路重要性进行综合评估。首先,提出计及传输裕度率的有功输电介数指标,以衡量支路的传输能力及其在电网拓扑结构中的重要度;然后,提出基于改进潮流转移熵的冲击性指标,以量化支路开断对系统造成的潮流冲击;最后,建立了包括有功输电介数和冲击性指标的支路综合重要度评估指标,以充分衡量支路在电网中的重要性。利用IEEE 39节点系统进行仿真,其仿真结果证明了该方法有效且合理。     

基于最大流理论的电力网关键线路和节点辨识

从结构性视角提出一种准确辨识电力网关键线路和节点的方法。该方法基于网络最大流和复杂网络理论,定义传输贡献度作为电力网关键线路和节点辨识依据,表征它们对实现电力网电能传输功能体现出的承载和贡献能力。该方法克服了现有研究中假设潮流沿着母线间最短路径传输的缺陷,依据网络整体结构考虑不同电源—负荷节点对间所有参与功率传输的路径;同时将电力网作为有向加权网络考虑,计及了线路最大有功传输容量约束,物理背景更符合电力工程实际。对IEEE 39节点系统进行仿真计算并将结果与现有方法对比,验证了所述方法的合理性和有效性。     

Advanced modeling of the multicontrol functional static synchronous series compensator (SSSC) in Newton power flow

The static synchronous series compensator (SSSC) is one of the recently developed flexible AC transmission system (FACTS) controllers. The SSSC coupled with a transformer is connected in series with a transmission line. This paper describes a multicontrol functional model of the SSSC for power flow analysis, which can be used for steady state control of one of the following parameters: (1) the active power flow on the transmission line; (2) the reactive power flow on the transmission line; (3) the voltage at the bus; and (4) the impedance (precisely reactance) of the transmission line. Furthermore, the model can also take into account the voltage and current constraints of the SSSC. The detailed implementation of such a multicontrol functional model in Newton power flow algorithm is presented. A special consideration of the initialization of the variables of the SSSC in power flow analysis is also proposed. Numerical examples on the IEEE 30-bus system, IEEE 118-bus system, and IEEE 300-bus system are used to illustrate the feasibility of the SSSC model and performance of the Newton power flow algorithm.     

Identification of wheeling paths by an extended sensitivity analysis

This paper proposes a practical method for identifying wheeling paths in deregulated electricity markets based on an extended sensitivity analysis. Using this method, it becomes possible to decide the proper and fair wheeling rate according to the degree of burden on transmission lines by each power flow transaction. Moreover, a wheeling rate based on the real power flow burden is also an important signal to new power suppliers in the markets. In order to show the validity of the proposed method, a series of simulations on the IEEE 30-bus test system were conducted.     

计及不确定性的预想事故自动选择区间方法

由于发电机出力和负荷需求具有不确定性,引入区间分析方法来处理电力系统静态安全分析中的不确定性问题.利用对区间线性方程组求解的区间直流潮流算法来计算发电机和支路开断后的潮流;提出一种新的改进的对区间进行大小比较的可信度量度函数.在此基础上,提出和实现了计及不确定性的电力系统预想事故自动选择的区间方法.采用5母线算例系统、IEEE 14母线算例系统和中国某省调电网实际系统对算法进行了验证,将文中算法与不计不确定性的传统分析方法以及概率方法相比较,证实了在静态安全分析中计及不确定性的必要性和文中方法的有效性及应用价值.