Load flow tracing in power systems with circulating power

Power flow tracing is very important to open access for loss allocation, congestion analysis and reactive power pricing, etc. In a previous paper, power flow tracing of power systems without circulating power has been implemented. In this paper, two lemmas have been proved first which show the reasons for circulating power. Then graph theory is applied to detect the existence of circulating power. After that optimal power flow (OPF) approach is suggested to eliminate circulating power. The sequential quadratic programming is used for OPF solution. The computer tests on a 6-bus system and the IEEE 30-bus power system yield satisfactory results. The suggested method is suitable for both active and reactive power flow tracings of power systems with circulating active and reactive power.     

Embedding sensitivity theory in ordinal optimization for decentralized optimal power flow control

In this paper, the decentralized optimal power flow with continuous and discrete control variables problem is firstly formulated as a NP-hard optimization problem - Block Additive constrained with Continuous and Discrete variables (BACD) problem. Secondly, an algorithm of embedding sensitivity theory (ST) in ordinal optimization (OO), abbreviated as STOO, is proposed for solving this NP-hard optimization problem. The STOO algorithm consists of three stages and three models of performance evaluation. The proposed method not only copes with the computational complexity due to huge solution space but also obtains a good enough solution with high probability guaranteed by the OO theory. Finally, this work demonstrates the computational efficiency of the STOO algorithm via various tests on the IEEE 118-bus and 244-bus systems partitioned into four subsystems using a 4-PC network and compares the results with those obtained using other heuristic methods, Genetic Algorithm, Tabu Search, Ant Colony Optimization and Simulated Annealing. Test results show the validity, robustness and excellent computational efficiency of the STOO algorithm for obtaining a good enough solution.     

基于最优潮流的无功定价方法探讨

电力市场环境下精确可行的无功服务定价是近年来研究的热点问题。将无功发电机会成本和无功补偿设备的投资加入到最优潮流的目标函数中,并考虑旋转备用的重要性,加入旋转备用约束条件,提出了新的基于最优潮流的无功功率实时定价模型。并对IEEE4-57节点系统进行了测试,所得的无功电价既能涵盖大部分的无功生产费用,又能提供足够的经济信息。     

区域电力市场阻塞管理方法评述

电力市场化改革要求开放本地市场,开展跨区交易,促进竞争,其主要目的是提高市场效率,降低电价。但是,跨区交易同时也带来了一些重要问题,区域间的阻塞就是一个不可忽视的问题。对近年来国外提出的跨区域阻塞管理方法进行评述,比较了他们的特点,从中得出了一些结论,为进一步研究跨区交易的输电服务、制定合理的跨区交易的输电价格提供参考。并对我国的跨区域阻塞管理提出一些建议。     

Security constrained optimal power flow considering detailed generator model by a new robust differential evolution algorithm

This paper presents a new multiobjective model, including two objective functions of generation cost and voltage stability margin, for optimal power flow (OPF) problem. Moreover, the proposed OPF formulation contains a detailed generator model including active/reactive power generation limits, valve loading effects, multiple fuel options and prohibited operating zones of units. Furthermore, security constraints, including bus voltage limits and branch flow limits in both steady state and post-contingency state of credible contingencies, are also taken into account in the proposed formulation. To solve this OPF problem a novel robust differential evolution algorithm (RDEA) owning a new recombination operator is presented. The proposed RDEA has a minimum number of adjustable parameters. Besides, a new constraint handling method is also presented, which enhances the efficiency of the RDEA to search the solution space. To show the efficiency and advantages of the proposed solution method, it is applied to several test systems having complex solution spaces and compared with several of the most recently published approaches.     

电力市场阻塞管理综述

在电力市场环境下，为了确保电力系统安全经济运行，需要对输电系统进行有效的管理。阻塞管理是其核心问题。随着电力市场研究的深入，阻塞管理及其定价已成为研究的热点，并发表出版了大量论文和专著。文中对阻塞管理这一领域的研究进行了简要的分类综述，并力图涵盖这一研究领域的各个方面。     

LMP机制下可中断负荷用于阻塞管理的最优调度方法

节点边际价格LMP（Locational Marginal Price）在解决交易的公平性和电网阻塞方面具有很大的优势,它从时间和空间两个层面反映电力系统的运行成本。可中断负荷作为需求侧管理的重要手段,可以有效地缓解阻塞。文中对发电出力再调度和可中断负荷量进行了均衡分析,提出了LMP机制下可中断负荷用于阻塞管理的最优调度原则。验证了可中断负荷在降低节点电价、增加社会效益以及解决阻塞方面的优势。文中采用IEEE30节点系统进行仿真,证明了该理论的正确性和合理性。     

Centralized optimal position control for active magnetic bearings: comparison with decentralized control

This paper discusses a closed-loop centralized control for a multi-input multi-output active magnetic bearing system. A genetic algorithm for design and a credible comparison of different controller structures are proposed. The evaluation of the design trade-offs of linear-quadratic and loop transfer recovery controllers are studied. The model-based controllers are compared with the classical PID controller and the cascaded PI/PD controller. The properties of the tested control configurations are examined using maximum singular values of the output sensitivity function of the closed-loop system and the tolerated disturbance at the input of the plant. Furthermore, indices such as measured peak output sensitivity, singular values of the uncertain control system, responses to the step reference position, step disturbance, and impulse force disturbance are examined. A good agreement between the simulation and the experimental results from the test-rig is shown.     

Applications of computational intelligence techniques for solving the revived optimal power flow problem

Computational intelligence tools are attracting added attention in different research areas and research in power systems is not different. This paper provides an overview of major computational issues with regard to the optimal power flow (OPF). Then, it offers a brief summary of major computational intelligence tools. A detailed coverage of most OPF related research work that make use of modern computational intelligence techniques is presented next.     

基于交流灵敏度的电能交易与输电权的统一拍卖

最优潮流程序便于实现线路有功功率和有功网损的交流灵敏度的计算和分析,且基于交流灵敏度信息的输电权计算可以更好地匹配实际潮流,故采用交流灵敏度信息作为市场交易的依据。同时,简化的市场结构可以降低电力市场交易成本和提高市场交易效率,由于电能交易同输电权交易具有相同的市场拍卖形式,因此以交流灵敏度信息为基础,建立了点对点输电权、基于潮流的输电权和电能交易的统一拍卖市场。提出的拍卖模型在数学上是一个线性规划问题,可以利用成熟的线性规划方法进行解算。这种统一市场实现了电能交易与输电权交易的全面优化,也为市场参与者在同一市场下提供了更多的选择。IEEE9节点算例证明了该方法的有效性。     

An optimal power flow plus transmission costs solution

This paper is aimed at the solution of the optimal power flow (OPF) problem with embedded security constraints (OPF-SC) by the particle swarm optimizer. The major objective is to minimize the overall operating cost while satisfying the power flow equations, system security, and equipment operating limits. The overall operating cost is composed by the generation cost, transmission cost, and the consumer benefit. A modification of the conventional particle swarm optimizer (PSO) has been used as the optimization tool, which uses reconstruction operators and dynamic penalization for handling constraints. The reconstruction operators allow the increase of the number of particles within the feasible region. The power equations mismatch, loss active power transmission, and voltages are calculated by the Newton–Raphson method. To demonstrate its robustness, the proposed algorithm was tested on systems from the open literature. Several cases have been studied to test and validate the proposed approach.     

Power flow tracing based transmission congestion pricing in deregulated power markets

The objective of this paper is to propose a simple transmission congestion pricing scheme based on tracing principle by considering generator fixed cost, cost for incurring loss and transmission congestion cost. Restructuring has brought about considerable changes by the virtue of which electricity is now a commodity and has converted into deregulated type. Such a competitive market has paved way for innumerable participants. This concept of restructuring has led to overloading of transmission lines. In this paper, power flow tracing has been employed by using suitable optimization algorithm, where the real power generation has been maximized. Congestion in the transmission line has been produced in a new fashion by maximizing the real power demand. The power flow under normal operating condition and congestion is determined and hence the difference in power flow is estimated. Based on the estimated power flow difference, the transmission line congestion cost is computed. Pool model and bilateral model has been considered in simulation study to introduce the concept of deregulation. The proposed method is tested and validated on Modified IEEE 30 bus test system and Indian utility 69 bus test system.     

IPP selection based on contingency analysis and optimal power flow

Recently the deregulation of the electric power industry has progressed worldwide. In Japan the electric power industry law was revised to achieve a reduced electricity price in 1995, and competition in the power generation market was started in Japan. Moreover, the retail wheeling to large customers was launched in March 2000. Under this situation, IPP selectors (electric power utilities) have to think about efficient connection to existing systems by which they have select IPPs considering not only the cost but also the future demand. Therefore, in order to achieve efficient connection of IPPs to the existing systems some selection guidelines are needed. What IPP selectors want to know is “where” and “how much” in the existing system they want to have IPPs. It is thought that knowing good connecting point(s) and the appropriate capacity of IPPs becomes one of the IPP selection guidelines. In this paper, we propose a method by which we can determine the connecting point(s) and the appropriate capacity of IPPs to plan the appropriate electric power system for the future. The proposed method in which IPP selectors can select from both sides of reliability and economy is verified using simulations. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 16–25, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10037     

基于可中断负荷的新型输电阻塞调度研究

可中断负荷管理是电力需求侧管理的一项重要内容。在电力市场条件下，传统的阻塞调度方法往往会使得阻塞线路节点的电价攀升许多，在对可中断负荷应用于阻塞管理的可行性分析的基础上，提出了一种新型的输电网络阻塞调度方法，利用最优潮流辅助以可中断负荷控制加以实现。与传统调度方法之间的经济比较以及3节点的算例表明，在电力市场条件下，应用最优潮流与可中断负荷控制相结合的阻塞调度方式能够有效地降低电网的阻塞成本，为电力用户带来尽可能大的收益，因而值得推广和应用。     

A fast interactive optimal load management algorithm under time-varying tariffs

A new approach to electricity tariff structuring, in which the tariff is varied continuously according to the actual production cost of electricity, has attracted many research workers. This paper begins by defining an analytical framework, using which each consumer is able to maximize his returns. Under this framework, a conceptually simple and yet computationally efficient algorithm has been developed to help each consumer in achieving his own goal. Based on the method of Lagrange multipliers, each method for improving the consumption pattern is ranked according to its incremental cost of implementation. In the first numerical example the algorithm provides a medium-size industrial consumer with the choice between self-generation and load shifting. In the second numerical example well-managed loads are shown to make good returns for the supplier and the resulting load factor is improved, leading to savings in fuel and capital costs.     

Stochastic optimal power flow incorporating offshore wind farm and electric vehicles

In this paper, an optimal power flow model of a power system, which includes an offshore wind farm and plug-in electric vehicles (PEVs) connected to grid, is presented. The stochastic nature of wind power and the uncertainties in the EV owner’s behavior are suitably modelled by statistical models available in recent literatures. The offshore wind farms are assumed to be composed of doubly fed induction generators (DFIGs) having reactive power control capability and are connected to offshore grid by HVDC link. In order to obtain the optimal active power schedules of different energy sources, an optimization problem is solved by applying recently introduced Gbest guided artificial bee colony algorithm (GABC). The accuracy of proposed approach has been tested by implementing AC–DC optimal power flow on modified IEEE 5-bus, IEEE 9-bus, and IEEE 39-bus systems. The results obtained by GABC algorithm are compared with the results available in literatures. This paper also includes AC–DC optimal power flow model, implemented on modified IEEE-30 bus test system by including wind farm power and V2G source. It has been shown that the uncertainty associated with availability of power from wind farm and PEVs affects the overall cost of operation of system.     

An autonomous decentralized control mechanism for power flow in an open electric energy network

This paper discusses a power flow control mechanism for the “open electric energy network” (OEEN), which has been studied by the authors as a demand-side network suitable for a free market of electricity. The important concept of OEEN is that electric energy is treated like a packet of mail, with information about the sender (power producer) and the receiver (consumer). The control mechanism discussed in this paper is called the electric energy router and includes an energy storage device. The electric energy router controls the storage device in such a way that the “electricity packet” reaches a specified consumer from a specified power producer autonomously and in the distributed manner. This paper shows that optimal control theory can be applied to determine the control action of the electric energy router. The obtained optimal control action minimizes the difference between the load pattern of the consumer and the supply pattern of the router under the inequality constraints of energy storage capacity. A numerical example is given in order to check the validity of optimal control theory application. In order to manufacture a small-scale electric energy router for experiments, its basic structure and power control performance are studied through simulation studies. © 1998 Scripta Technica. Electr Eng Jpn, 121(4): 28–37, 1997     

Energy and ancillary service dispatch through dynamic optimal power flow

This paper presents an approach based on dynamic optimal power flow (DOPF) to clear both energy and spinning reserve day-ahead markets. A competitive environment is assumed, where agents can offer active power for both demand supply and ancillary services. The DOPF jointly determines the optimal solutions for both energy dispatch and reserve allocation. A non-linear representation for the electrical network is employed, which is able to take transmission losses and power flow limits into account. An attractive feature of the proposed approach is that the final optimal solution will automatically meet physical constraints such as generating limits and ramp rate restrictions. In addition, the proposed framework allows the definition of multiple zones in the network for each time interval, in order to ensure a more adequate distribution of reserves throughout the power system.     

A decentralized control system for stabilizing multimachine power systems

A decentralized control system is studied for stabilizing multimachine power systems. A longitudinal power system with three areas, each having one machine, is considered in this study. A decentralized control design method is proposed, which is based on the optimal regulator theory. First a centralized control system is designed without any consideration on whether state variables are all available or not. Second a pseudo-decentralized control system is designed by omitting control gains corresponding to state variables which give hardly any effects on the power system stability. It is found that only one variable of phase angle of each machine is absolutely necessary for the pseudo-decentralized control system. This leads to an idea based on power system engineering, that is to say, new variables of tieline power flow are introduced in the decentralized control system design to substitute for the phase angle of each machine. Thus a decentralized control system for power system stability can be designed using the new variables of tieline power flow. It is demonstrated from simulation studies that the decentralized control system improves even longitudinal power system stability as well as the centralized control system.