Comparison of Centralized and Decentralized Systems in Power System Restoration

This paper proposes a multiagent approach to decentralized power system restoration for distribution system networks and presents a comparison of centralized and decentralized systems for power system restoration. Numerous studies have been conducted on power system restoration problems. From the viewpoint of system structures, this research can be divided into two categories: centralized systems and decentralized systems. In this study, we solve a power system restoration problem for a power distribution network by two different methods: mathematical programming (MIP) and the proposed multiagent‐based method (MAS). The proposed multiagent system consists of several distributing substation agents (DSAGs) and load agents (LAGs). An LAG corresponds to the customer load, and a DSAG supplies electricity to the LAG. From the simulation results, it can be seen that the proposed system can reach the right solution by making use of only local information and that the solution quality is better than that of the centralized system (MIP). This means that the proposed multiagent restoration system is a promising approach to larger scale distribution networks.     

A Voltage Control Method for a Distributed Line Feeder by means of Multiagent Approach

This paper proposes a method for the coordinated control of power factor by means of a multiagent approach. The proposed multiagent system consists of two types of agent: single feeder agent (F_AG) and bus agent (B_AG). In the proposed system, an F_AG plays as an important role, which decides the power factors of all distributed generators by executing the load flow calculations repeatedly. The voltage control strategies are implemented as the class definition of Java into the system. In order to verify the performance of the proposed method, it has been applied to a typical distribution model system. The simulation results show that the system is able to control very violent fluctuation of the demands and the photovoltaic (PV) generations.     

A multi‐agent approach to unit commitment

This paper proposes a multiagent system to power system unit commitment problems. Multiagent is a new paradigm for developing software applications. Coordinating the behavior of autonomous agents is a key issue in agent‐oriented programming techniques today. Recently, agents are being used in an increasingly wide variety of applications, ranging from comparatively small systems such as E‐mail filters to large, open, complex systems such as air traffic control. Though some agent frameworks have been proposed in the power system field, the number of studies is limited. In this paper, we developed a power system unit commitment application by multiagent architecture. Our multiagent system has the following characteristics: (1) The system consists of a single facilitator agent, two mobile agents, and one or more generator agents which are elements of power system network. (2) The facilitator agent is developed to act as a manager for the process by using the singleton design pattern. The mobile agents migrate to generator‐agents to increase or decrease their power generations. The generator agents have their operational data. (3) Message object is developed to communicate between the agents using KQML‐like object. The proposed approach is applied to a simple model system, and the results show that the multiagent system is an efficient decentralized approach for solving power system unit commitment problems. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(2): 41–47, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10057     

Development of power system reliability analysis program with consideration of system operation

This paper describes a new program which analyzes the reliability of composite power systems with consideration of power system operational aspects. It uses the sequential Monte Carlo method and calculates annual risk indices for each load point. The program deals with the system problems involved in load flow, voltage, frequency, and small‐signal stability if necessary. The distinctive feature of the program is consideration of power system operation in a sequential manner, such as generation dispatch and system restoration after equipment failure. This makes possible the evaluation of both power system planning and operation from the reliability point of view. Several new methods of reducing calculation time are developed and implemented, including the concurrent LP/load flow method, which improves solvability. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(4): 20–31, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20138     

A multiagent approach to power system normal operation

Recently, the electric utility industry worldwide has been facing pressure to be deregulated or restructured in order to increase its efficiency, to reduce operational cost, or to give consumers more alternatives. For this aspect, a great deal more research is needed to achieve a better, intelligent knowledge process. The present centralized system for power system control, operation, and planning must be remodeled to cope with these situations. With the promotion for the deregulation of the electric power system, the definition of the objective function for the optimization problem such as outage work operation for electric power systems is becoming critical. Currently, agents are an intense focus in many subfields of computer science and artificial intelligence. Agents are being used in an increasingly wide variety of applications. In this paper, we developed a power system normal operation application by multiagent architecture. Our multiagent system consists of several facilitator agents, equipment agents, and switch‐box agents. Facilitator agent acts as a manager for negotiation process between agents. Equipment agent corresponds to the element of the electric power system, such as bus, transformer, and transmission line, while switch‐box agent is the pseudo object which consists of neighboring current breakers and disconnecting switches. The proposed system realizes the appropriate switching operations by interacting with corresponding agents. The proposed approach is applied to a simple network, and the results show that the proposed multiagent system is an efficient decentralized approach for solving power system normal operations. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 146(4): 26–33, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10227     

Permutation-based Power System Restoration in Smart Grid Considering Load Prioritization

Abstract

In the smart grid environment, a power system restoration plan with flexibility is needed to improve reliability and efficiency in an automated way. Traditional system restoration methods based on fixed time intervals may not meet the requirement. This article proposes a new permutation-based model for power system restoration within an optimized flexible duration considering available generator capability and load prioritization. By utilizing this new model, power system restoration is formulated as a permutation-based combinatorial optimization problem to maximize the restored load per unit time. Finally an action-by-action flexible time schedule is obtained for generator startup. A novel quantum-inspired evolutionary algorithm, called the quantum-inspired differential evolutionary algorithm, has been applied to solve this problem due its to high population diversity and fast convergence. The effectiveness of the proposed restoration approach has been validated using IEEE 39- and 57-bus systems.     

A novel approach to deliverable power in low‐voltage DC distribution system on the basis of voltage stability

This paper proposes that a deliverable power through a low‐voltage DC distribution system has an upper limitation. The upper limitation of the deliverable power, P_lim, is explained on the basis of a voltage instability phenomenon occurring for the load with a voltage sensitivity below 1. From theoretical‐calculation results, it is pointed out that P_lim diminishes with augment in the distribution‐line length. This phenomenon becomes more distinct for the higher distribution‐line inductance per unit length. Connection of the capacitor to the receiving end of the distribution line is discussed as a method for rising P_lim. Measurements of the voltage waveform at the load terminals successfully support P_lim derived from the theoretical calculation. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

考虑多代理供电恢复系统通信失效的配电网CPS风险评估

提出一种考虑多代理供电恢复系统通信失效的配电网信息物理系统(CPS)风险评估方法。该方法将整个供电恢复过程分解为多个包含输入和输出的子任务,当通信系统失效时,依赖于失效通信链路的子任务将输出无效值,进而影响供电恢复的效果。通过计算不同供电恢复系统失效状态下的负荷缺额、恢复容量以及各个状态的概率,可以得到供电恢复后的电力不足期望值,并据此构建配电网CPS风险评价指标。通过计算并比较风险指标对各条通信链路丢包率的灵敏度大小,可以确定关键通信链路,并指出在通信系统的设计中应差异化提升这些通信链路的可靠性。最后,通过典型算例验证了所述方法的有效性。     

Short‐term load forecasting using informative vector machine

In this paper, a novel method is proposed for short‐term load forecasting, which is one of the important tasks in power system operation and planning. The load behavior is so complicated that it is hard to predict the load. The deregulated power market is faced with the new problem of an increase in the degree of uncertainty. Thus, power system operators are concerned with the significant level of load forecasting. Namely, probabilistic load forecasting is required to smooth power system operation and planning. In this paper, an IVM (Informative Vector Machine) based method is proposed for short‐term load forecasting. IVM is one of the kernel machine techniques that are derived from an SVM (Support Vector Machine). The Gaussian process (GP) satisfies the requirements that the prediction results are expressed as a distribution rather than as points. However, it is inclined to be overtrained for noise due to the basis function with N² elements for N data. To overcome this problem, this paper makes use of IVM that selects necessary data for the model approximation with a posteriori distribution of entropy. That has a useful function to suppress the excess training. The proposed method is tested using real data for short‐term load forecasting. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(2): 23– 31, 2009; Published online in Wiley InterScience ( www. interscience.wiley.com ). DOI 10.1002/eej.20693     

An improved load flow technique based on load current injection for modern distribution system

This paper presents load current injection based improved load flow (LF) technique for modern distribution system. The proposed LF technique is derived by promulgating the concept of conventional backward forward sweep technique. This proposed technique uses a single load current to bus voltage (LCBV) matrix to perform both the backward and the forward sweeps of power flow calculation in a single step. Utilizing the concept LCBV, the bus voltages can be determined, directly, from the load current injections. Due to the distinctive solution technique of the proposed approach, the time-consuming lower–upper factorization and forward–backward substitution or any derivative operation required in the traditional LF technique are no longer necessary. These unique features make the proposed technique faster in operation. The proposed approach is flexible enough to accommodate any sort of change in network structure due to reconfiguration. Along with the modeling of various equipments of distribution system (viz. distribution transformer, voltage regulator, voltage dependent loads, distributed generations, etc.), special treatments for weakly meshed system are also presented in this work. It is experimented on several test systems of varying complexities (viz. 28-, 69- and 30-bus balanced radial distribution system (RDS), 10-bus and IEEE 34-bus unbalanced RDS and 33- and 69-bus weakly meshed system) and the obtained results demonstrate the effectiveness of the proposed approach while comparing to the existing methodologies. Furthermore, it is revealed that the proposed algorithm is, computationally, faster, robust and more suitable for modern distribution network than the contemporary techniques available in the state-of-the-art literature.     

A Multiagent‐Based Microgrid Operation Method

In this paper, we propose an autonomous microgrid operation using a multiagent approach. The proposed multiagent system consists of seven types of agent: a single microgrid controller agent (MGC), several load agents (LAGs), several gas‐turbine (gas‐engine) agents (GAGs), several photovoltaic generation agents (PVAGs), several wind‐turbine generation agents (WTAGs), several battery agents (BAGs), and a single grid agent (GridAG). In a microgrid, LAGs act as consumers or buyers, GAGs, PVAGs, and WTAGs act as producers or sellers, and BAGs act as prosumers or sellers/buyers. In order to verify the performance of the proposed system, it is applied to a simple model system with different electrical power prices. From the simulation results, it can be seen that the proposed multiagent system can perform microgrid operations efficiently.     

An innovative approach for solving the restoration problem in distribution networks

An effective heuristic graph-based approach is proposed in this paper for solving the service restoration problem in distribution networks. Minimisation of the de-energised consumers’ load and reduction of the number of switching operations were considered in this service restoration application. A suitable assignment of the weighting coefficient to all branches in a de-energised area was used to decrease the number of switching operations. Prim's algorithm for finding of the minimum spanning tree logic was used to realise this approach. Other applications necessary for the optimal performance of the service restoration application were also developed and tested in this study (e.g., load flow, load reallocation of overloaded network elements, generation of the sequence of switch actions, etc.).     

Improved multilevel bipartitioning for controlled power system islanding

Nowadays interconnected power systems work close to their limits because of increased economic benefits. If a severe disturbance occurs in any part of the interconnected power system, it can be propagated through it. If no intelligent supervisory action is taken, a power system may be driven into an emergency state which could either cause system collapse by natural islanding or total system blackout. One possible measure to be put in effect in an emergency state is controlled power system islanding. In this paper, our previously proposed multilevel approach for controlled islanding is improved by using slow coherency grouping of generators in the aggregation phase. The approach has been applied to the IEEE 118 bus power system. The results indicate that the best partitioning of the power system is obtained with minimum generation/load imbalance in the islands, and with the coherent groups of generators maintained in each island making the restoration easy. A comparison of the computational complexities involved in the spectral, multilevel kernel k‐means and the improved multilevel approaches is made by applying these methods to the IEEE 9 bus, the IEEE 30 bus, the IEEE 39 bus, the IEEE 57 bus, the IEEE 118 bus, the IEEE 300 bus, the 2383 bus Polish and the 2746 bus Polish power systems to show the suitability of the proposed approach for controlled islanding of large‐scale power systems. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于坐标旋转变换的配电系统快速解耦潮流计算方法

配电系统中各支路的电阻与其电抗的比值较大,因此,经典的快速解耦潮流计算方法不适用于配电系统潮流计算。提出了一种坐标旋转变换方法,并将这种变换方法与经典的隐式Zbus高斯方法相结合,导出了配电系统的解耦潮流计算方法。以IEEE 33节点、IEEE 69节点和一个实际的145节点配电系统为例,对提出的解耦潮流算法进行了测试。结果表明,所提出的解耦方法不影响经典的隐式Zbus高斯方法的收敛性,因而是一种高效、实用的快速潮流计算方法。     

Determination method for loss‐minimum configuration considering reconnection of distributed generators

In the field of electrical power system, various approaches, such as utilization of renewable energy, loss reduction, and so on, have been taken to reduce CO₂ emission. So as to work toward this goal, the total number of distributed generators (DGs) using renewable energy connected into 6.6‐kV distribution systems has been increasing rapidly. The DGs can reduce distribution loss by appropriate allocation. However, when a fault occurs such as distribution line fault and bank fault, DGs connecting outage sections are disconnected simultaneously. Since the simultaneous disconnection of DGs influences restoration configuration and normal configuration after the restoration, it is necessary to determine the system configuration in the normal state considering simultaneous disconnection of DGs. In this paper, the authors propose a computation method to determine the loss minimum configuration in the normal state considering reconnection of DGs after simultaneous disconnection by fault occurrence. The feature of determined loss minimum configuration is satisfying with operational constraints even if all DGs are disconnected from the system. Numerical simulations are carried out for a real‐scale distribution system model with 252 sectionalizing switches (configuration candidates are 2²⁵²) and 120 DGs (total output is 38.46 MW which is 23% of total load) in order to examine the validity of the proposed algorithm. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(4): 7–14, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21142     

一种快速高效的配电网供电恢复算法

配电网故障后的供电恢复是一种带约束的多目标优化问题。文中采用一种快速高效的搜索策略,建立满足系统电流、电压约束的可行方案集,然后基于模糊集技术针对开关操作次数、未失电区负荷的转换量、系统紧急备用容量等指标对各候选方案进行评估,为运行人员从中选择并执行最为理想的恢复方案提供了根据。算例仿真证明了这一方法的效性。     

三相四线制D-STATCOM/HESS系统在配电网中的应用及其仿真研究

针对配电网中存在谐波、无功以及负荷频繁波动等问题,提出了含混合储能(HESS)的三相四线制配电网静止同步补偿器(D-STATCOM),实现配电网无功补偿和谐波抑制,平抑负荷有功功率波动。首先,针对三相四线制配电网,通过对传统ip- iq谐波电流检测法改进,实现了对负荷所需的有功、无功和谐波补偿电流的准确检测。在此基础上,将超级电容器和铅酸蓄电池组成的混合储能系统引入到补偿装置中,实现了对配电网有功、无功和谐波电流的全补偿。结合不同储能装置的充放电特性,采用协调控制方法,确保系统对配电网能量的迅速准确补偿。最后结合某建筑配电网实际负荷,验证了三相四线制D-STATCOM/HESS系统及其控制算法在谐波抑制、无功补偿和平滑负荷有功波动方面的有效性。     

面向弹性提升的智能配电网远动开关优化配置模型

信息物理系统的深度融合为配电网动态、远程控制提供了技术支持.远动开关(RCS)可以在配电网遭受极端事件攻击后隔离故障,缩小故障区范围,参与网络重构恢复负荷.提出了RCS的鲁棒优化配置模型,在规划阶段完成配置RCS,以实现遭受极端事件后配电网失负荷损失最小化.基于防御-攻击-防御(DAD)框架,在第1层,规划人员确定RC...     

Unified Fast Decoupled Load Flow in a Parallel Distributed Computation Framework

Abstract

This research proposes a parallel and distributed computation approach for the fast decoupled load flow (FDLF) analysis applicable to both transmission and distribution networks of large electrical power systems. In this approach, the overall repetitive FDLF computations are performed by the respective control centers identified for each sub-system, the sub-systems being formed by partitioning the system through a network tearing procedure splitting the identified buses. The data of each subsystem are stored at their own control centers and hence the subsystems are solved using message passing distributed memory architecture. The computations performed by the control centers in various sub-systems are coordinated from a regional control center. The investigations on IEEE 118 bus standard test system indicate that the proposed approach provides faster solution than the conventional approach, without affecting the solution accuracy. The effectiveness of the proposed technique over the conventional approach become more visible when it is applied for the load flow analysis of large scale systems spread over a wide geographical area.     

A study of a two‐stage maximum power point tracking control of a photovoltaic system under partially shaded insolation conditions

A photovoltaic (PV) array shows relatively low output power density, and has a greatly drooping current–voltage (I–V) characteristic. Therefore, Maximum Power Point Tracking (MPPT) control is used to maximize the output power of the PV array. Many papers have been reported in relation to MPPT. However, the current–power (I–P) curve sometimes shows multi‐local maximum power points mode under nonuniform insolation conditions. The operating point of the PV system tends to converge to a local maximum output power point which is not the real maximal output point on the I–P curve. Some papers have tried to avoid this difficulty. However, most of those control systems become rather complicated. The two‐stage MPPT control method is proposed in this paper to realize a relatively simple control system which can track the real maximum power point even under nonuniform insolation conditions. The feasibility of this control concept is confirmed for steady insolation as well as for rapidly changing insolation by simulation study using software PSIM and LabVIEW. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(4): 39–49, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20188