Multiagent‐Based Electric Power Interchange between Microgrids

In this paper, we propose a multiagent‐based electric power interchange method between microgrids (MGs). The proposed multiagent system consists of eight types of agent: a single micro virtual power plant (MVPP) agent , several MG controller agents (MGCs), several load agents, several gas turbine (gas engine) agents, several photovoltaic generation agents, several wind turbine generation agents, several battery agents, and a single grid agent. In the proposed system, the MVPP plays an important role, facilitating electric power exchange between MGCs. Simulation results suggest that the proposed multiagent system could improve the load factor and reduce the MG operation cost.     

A multiagent‐based microgrid operation method considering charging and discharging strategies of electric vehicles

In this paper, we propose a multiagent‐based microgrid (MG) operation method considering charging and discharging electric vehicles (EVs). The proposed system consists of five types of agents: single microgrid controller agent, several load agents, several gas turbines/engine agents, several photovoltaic generation agents, and several electric vehicle agents. In the proposed method, the load balancing can be realized by suppressing sudden fluctuations in supply and demand balance due to the synchronization of charging and discharging of EVs. From the simulation results, it can be seen that the proposed multiagent system could realize the load equalization in MG.     

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     

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.     

含分布式电源的配电网供电恢复的多代理方法

针对含分布式电源的配电系统,特别在考虑了由分布式电源和负荷组成微网运行的情况下,建立了以恢复负荷最多、开关操作数最少为目标的供电恢复模型。在提出配网调度中心、微网、分布式电源三者的分层协调控制策略的基础上,应用多代理理论,建立了一个由全系统控制协调代理（CAG）、微网控制代理（MGAG）、分布式电源代理（DGAG）以及母线代理（BAG）组成的多代理系统,在保证配电网辐射状运行、满足配电网电压与电流及馈线容量等约束条件的情况下进行供电恢复。通过分析一个含2个变电站、14条母线和4个分布式电源的配电系统的单重及多重故障供电恢复问题验证了该方法的有效性。     

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     

Multi-agent approach to modeling and simulation of microgrid operation with vehicle-to-grid system

This study presents the modeling and simulation of a vehicle-to-grid (V2G) system within a microgrid considering the requirements of various components of the microgrid system such as distributed renewable energy resources (DERs), plug-in electric vehicles (PEVs) and non-PEV loads. The system modeling is carried out using an agent-based methodology where components of the microgrid are modeled as agents. The use of PEV car batteries collectively as a virtual power plant (VPP) enables PEVs to not only act as loads but as energy sources alongside DERs such as wind and solar power generation. The smart control and scheduling of the charging and discharging of the PEVs by the charging station can be used to achieve sustainable integration of a high number of PEVs in the microgrid power system. In addition to simulating a microgrid operation, results of this study show how agents’ behavior change based on factors such as penetration of renewable energy, penetration of PEVs, travel pattern of PEV drivers and price of energy generation.     

含压缩空气储能的能源互联微网型系统优化配置

首先构建了含分布式光伏、压缩空气储能（compressed air energy storage, CAES）、需求侧响应、燃气轮机等设备的能源互联微网型系统模型。在此基础上以安装成本、能耗成本和需求侧响应成本等构成的年运行费用最低为优化目标,分析对比不同场景下分布式光伏电池组数量、能源互联微网中设备的配置情况及CAES、需求侧响应和电动汽车入网（vehicle to grid, V2G）技术对设备容量配置和微网中各类成本的影响。特别的,考虑了CAES透平机透平压力、透平温度、需求侧响应比例等参数及有无V2G对微网系统影响。算例结果表明,所提模型能合理化能源互联微网中设备容量配置和降低能源互联微网年运行费用。     

风柴储孤岛微网的风险评估体系研究及应用

以孤岛运行模式下的风柴储微网为研究对象,本文提出了一种全新的孤岛微网风险指标评价体系,即负荷损失指标(Load Loss Risk, LLR)和电源损失指标(Power Loss Risk, PLR),从用电和发电两个角度全面评估其风险水平。首先,对风柴储微网各元件进行建模,特别是采用马尔可夫链建立了风电机组多状态可靠性模型,体现了风速变化的连续性。其次,在微网各元件可靠性模型的基础上,模拟微网的运行情况,并采用全新的风险评估指标量化其运行风险。最后,以欧洲典型低压风柴储微网为例,算例验证了本文所提指标的合理性,并对不同风速、风机故障率、风电装机容量以及储能容量对微网孤岛运行风险的影响进行了灵敏度分析,所得评估结果可为风柴储孤岛微网的容量配置以及规划运行提供参考。     

A distributed non-Lipschitz control framework for self-organizing microgrids with uncooperative and renewable generations

This paper investigates the design of robust distributed voltage and frequency control for a self-organized microgrid. A multiagent distributed secondary hierarchy is proposed using control Lyapunov function. Power resources are categorized as controllable and uncontrollable distributed generations (DG). Controllable DGs are exchanging information with neighbor DGs through agents at communication layer. The agents communicate to restore the voltage and frequency to their nominal references. Furthermore, the proposed scheme is robust against the insufficient data from uncontrollable DGs, since it provides an improved and stable operation even when there is no communication with uncontrollable DGs and loads. It can actively compensate for the random unknown demand and generation, by sharing the power mismatch in distributed droop architecture. It is shown that the suggested controller is capable of stabilizing an uncooperative microgrid in which not all DGs are cooperating. Also, the convergence speed of the system is improved using the finite-time controller. The performance and finite-time stability of a microgrid with partially-cooperative DGs is proved using Lyapunov theorem and is validated through numerical simulation. The results show improved transients, accurate steady state values for voltage and frequency control of a microgrid, and robustness against communication architecture variations. The impact of communication delays, the uncertainty in coupling gains of the communication links, and the time-interval between updating the controller and the states through communication are investigated.     

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.     

基于Multi-agent的微网控制模型研究

针对高渗透微电网接入配电系统后,给主网调度稳定运行和可靠性带来困难这一问题,基于Multi-agent提出一种新的微网控制模型,该模型将微网及内部单元作为a-gent节点行为,构建了微网的两层控制体系:对底层单元agent采用恒功率和恒频恒压控制方法;对上层微网agent,提出恒交换功率控制策略,使微电网在并网运行时表现为单一的可控负荷,微网与主网的交换功率维持恒定,减少主网的调度难度。通过建立微网两层控制体系相应的具体模型,并对两层控制体系之间的协同策略作具体分析,保证了微电网在不同运行模式下的稳定运行。在PSCAD中进行建模仿真,结果表明,该控制模型使微电网并网和孤网时均能可靠运行,且保证了对主网调度的友好性。     

Numerical inverse definite minimum time overcurrent relay for microgrid power system protection

Access of distributed generation gets complicated at the distribution level, and hence managing these systems effectively becomes highly challenging. Microgrids have been proposed as a way of integrating a large number of distributed renewable energy sources with a distribution system. They are low to medium voltage networks of small load clusters with distributed generation sources and storages. Microgrids can be operated in the islanded mode or the grid‐connected mode. If a microgrid is connected to the system, it is seen as a single aggregate load. One of the potential advantages of a microgrid is that it could provide more reliable supply to customers by islanding itself from the system in the event of a major disturbance. However, a major problem with microgrid implementation in islanded operation is designing a proper protection scheme. The fault currents for grid‐connected and islanded microgrids are significantly different. Additionally, high penetration of inverter‐connected distributed generation sources leads to conditions where no standard overcurrent protection method will work. Overcurrent protection is considered as the backbone of any protection strategy, especially in distribution systems. Distribution systems constitute the largest portion of the power system network, and therefore the diagnosis of faults in this system is a challenging task. Faults occurring in distribution systems will affect the reliability, security, and quality of a power system. Field‐processable gate array (FPGA) Xilinx Zynq‐based numerical overcurrent relay protection is provided to the microgrid that is operated in islanded mode. This results in faster discrimination and quicker isolation of the faulty section from the microgrid. This improves the reliability of the microgrid because the fault is rapidly diagnosed and isolated from the healthy part, thanks to the high‐speed operation of the 800‐MHz FPGA Xilinx Zynq‐based numerical overcurrent relay. This system is simulated using MATLAB Simulink SimPower system tool box and LabView software. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Construction and power generation characteristics of H2O turbine power generation system utilizing waste heat from factories

A new gas turbine power generation system has been proposed, in which the steam (H₂O) produced by utilizing waste heat from factories is used as the working fluid of gas turbine. A simulation model has been constructed to estimate power generation characteristics of the proposed system by adopting C++ language. It has been shown from simulation results that the proposed system has high exergetic efficiency, that is, the total exergetic efficiency is 46.3% and fuel‐based efficiency is 56.3% for a case where steam with a temperature of 275 °C produced from a garbage incineration plant is used. Sensitivity analysis has also been carried out when usable steam temperature and pressure is changed, together with the case when condenser outlet pressure is changed. Characteristics of a dual fluid gas turbine cycle power generation system (DFGT) have also been estimated in this study. It has been shown that the proposed system has 16.9% higher exergetic efficiency and 41.8% higher fuel‐base exergetic efficiency compared with DFGT. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 38–47, 2000     

Proposal and Evaluation of a New‐Type Cogeneration System for Energy Saving and CO2 Emission Reduction

The paper proposes a cogeneration system which generates four types of energy or material resources: electricity, steam, hot water, and freshwater. The proposed system can capture CO₂, and be constructed on the basis of a combined cycle power generation system which consists of a gas turbine and a back‐pressure extraction turbine. In the proposed system, power is produced by driving the gas turbine system. High‐pressure saturated steam with medium temperature is produced in the heat recovery steam generator by using gas turbine exhaust gas, and then superheated with a regenerative superheater in which the fuel is burned by using oxygen instead of air for driving the steam turbine generator. Water and CO₂ are recovered from the flue gas of the regenerative superheater. It has been estimated that the proposed system has a net power generation efficiency of 41.2%, a heat generation efficiency of 41.5%, and a total efficiency of 82.7%. Freshwater of 1.34 t/h and CO₂ of 1.76 t/h can be recovered. It has also been shown, when a case study was set and evaluated, that the proposed system can save 31.3% of energy compared with the conventional energy supply system, and reduce CO₂ emission by 28.2% compared with the conventional cogeneration system. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

考虑热负荷二维可控性的微网热电协调调度

考虑到区域内用户的热、电需求,近年来以微型燃气轮机为核心的热电联供系统在微网中得到广泛应用。如何协调调度微网的供热、供电,是提高可再生能源吸纳率、降低微网热电联供成本的关键。文中从用户供热舒适度的模糊性、微网供热系统的热惯性角度考虑,提出采用室内热舒适度指标将热负荷需求由传统的曲线转换为区间,从而使热负荷在各时间点上具有弹性;同时以自回归滑动平均(ARMA)模型描述供热系统多时段间的耦合关系,使供热量在时间轴上具有一定的可调节性。文中将上述两个特性统称为热负荷的二维可控性。算例分析了考虑热负荷二维可控性后,微网在孤网/并网运行时微型燃气轮机运行平稳性、弃风/光、购/售电量等方面,结果显示所述方法可有效减少热—电刚性耦合,为实现微网中热—电的时间平移和优化匹配提供了一种新思路。     

基于智能合约的电动汽车充电服务费自适应调整机制

为了解决传统集中式电动汽车充电服务费统一定价难以满足新型电力系统精度与灵活性需求的问题,提出了一种基于智能合约的电动汽车充电服务费自适应调整机制。通过建立考虑购售电双方收益的充电服务费优化模型,从购售电双方收益及负荷引导需求两方面对充电服务费进行优化;同时运用智能合约技术,制定更加精确、更具针对性的单座充电站的充电服务费调整策略。通过算例进行仿真验证,结果表明相较于传统定价模式,所提自适应定价模式下的负荷引导能力和交易双方的收益水平都具备显著优势。     

It takes a multiagent system to manage distributed systems

This article describes a new multiagent system for the management of distributed systems. The system is proposed to optimize the execution of management functions in distributed systems. The system includes the function of each agent and the interactions that occur among agents. The proposed system uses two mobile agents. The first is use to submit tasks to the subnetworks of the distributed system and the other collects results from these subnetworks. The proposed multiagent system is implemented using IBM aglets developed by Lange and Oshima with Java virtual machine (JVM)     

考虑阶梯式碳交易机制的微电网两阶段鲁棒优化调度

为减少微电网系统运行的碳排放量,同时考虑可再生能源出力不确定性对系统调度结果的影响,提出了一种基于鲁棒优化的微电网低碳经济调度模型。首先,利用两阶段鲁棒优化方法消除可再生能源出力不确定性对系统调度结果的影响。其次,将阶梯式碳交易机制引入系统的运行调度阶段,以减少微电网系统的碳排放量。然后,建立了包含风电、光伏机组、微型燃气轮机、燃料电池及储能设备的微电网低碳经济调度模型,以各设备运维成本、系统购能成本和碳交易成本之和最小为优化目标,采用C&CG算法对所提调度模型进行求解。最后通过算例对所提优化调度模型进行验证。结果表明：两阶段鲁棒优化方法能够有效提高系统抵御风险的能力、引入阶梯式碳交易机制则可有效减少微电网运行的碳排放量。     

可实现运行模式灵活切换的小型微网实验系统

为了能够对微网的运行特性进行深入的理论和实验研究,建立了一个小型实验室微网系统。该系统中的分布式电源采用光伏模拟单元和风机模拟单元,通过电力电子变换装置并入微网;系统以蓄电池为储能装置,并通过双向逆变器并入微网,用以维持微网的暂态功率平衡。当微网联网运行时,以外电网电压和频率为参考,蓄电池双向逆变器、光伏并网逆变器和风机并网逆变器采用恒功率控制;孤岛运行时,双向逆变器的控制策略切换为恒电压、恒频率控制,用以提供微网电压和频率参考。实验结果表明,该系统可以稳定地工作在联网模式和孤岛模式,并可实现二者之间的平滑切换,提高了能量供给的可靠性。