Hierarchical decentralized autonomous control in super‐distributed energy systems

This paper deals with a decentralized autonomous control strategy of a super‐distributed energy system with a hierarchical structure in order to reduce the complexity of control. In this paper, distribution systems are assumed to be composed of multiple small‐scale power systems in which many customers with dispersed generators exist. A small‐scale power system can be considered as a unit with a generator state and a load state, or as a customer with dispersed generators. Control components of small‐scale power systems are interconnected with each other and are used to operate distribution systems. An expanded decentralized autonomous control method for a super‐distributed energy system with a hierarchical structure is proposed on the basis of the Hopfield neural network. It is demonstrated that super‐distributed energy systems with a hierarchical structure can be controlled autonomously by applying the proposed method. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Multi‐agent‐based autonomous power distribution network restoration using contract net protocol

A novel multi‐agent‐based system based on the contract net protocol (CNP), intended to achieve a distributed approach to power distribution network restoration, is proposed. In the proposed system, agents are assigned to areas sectioned by switches and constantly exchange environmental information among themselves. The information is used to construct a CNP overlay network to guard against network accidents. The parameters of the CNP required for robustness and effectiveness are optimized by the genetic algorithm (GA) in the operation phase. When a network accident occurs, the agents restore power distribution service autonomously through the CNP overlay network constructed. Simulation experiments indicate that CNP allows an effective power distribution network restoration strategy to be created by cooperation among agents. ©2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(4): 56–63, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20661     

A distributed autonomous approach for bulk power system restoration by means of multi‐agent system

In recent years, the electric utility industry worldwide has been facing pressure to be deregulated. Also, the risk of blackout in large areas will increase. Actually, it is still vivid in our memory that the northeastern United States and southern Canada suffered the worst blackout in history. Consequently, a method to find the optimal solution rapidly is needed all the more. In this paper, we propose a new multi‐agent method for a bulk power system restoration. In order to demonstrate the capability of the proposed multi‐agent system, it has been applied to a model bulk power system, which consists of three local areas including 12 generating units and 12 loads, and three remote areas with 12 loads. A large number of simulations are carried out on this model network with changing conditions. The simulation results show that the proposed multi‐agent approach is effective and promising. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 69–76, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20485     

A control method for small‐scale DC power systems including distributed generators

This paper describes a DC micro‐grid system interconnecting distributed power generators. The system consists of five generation and control units: a solar‐cell generation unit, a wind‐turbine generation unit, a battery energy‐storage unit, a flywheel power‐leveling unit, and an AC grid‐interconnecting power control unit. The control method is proposed for suppressing the circulating current by detecting only the DC grid voltage. This method brings high reliability, high flexibility, and maintenance‐free operation to the system. The method pays attention to DC output voltage performance of each unit. Each of the power control units and the energy‐storage unit is controlled to act as a voltage source with imaginary impedance. On the other hand, each of the two generation units is controlled to act as a current source. The power‐leveling unit is controlled to act as a current source having the function of frequency selectivity like a high‐pass filter. A 10‐kW prototype system verifies experimentally the validity and effectiveness of the proposed control method for the DC‐grid system. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 86–93, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20603     

Three‐phase voltage control method by single‐phase distributed generators connected to islanded distribution network

We have proposed a concept model of emergency islanded operation by using distributed generators (DGs) such as photovoltaics, electric vehicles, or batteries, which can provide power to customers via undamaged distribution network in order to develop the resilient power system against large disasters, and it is named Islanded Distribution Network (IDN). Since there is no guarantee that the three‐phase generation system is interconnected to the IDN, the single‐phase DGs that are installed in the distribution network may be treated as main generators in the IDN operation. If the IDN has only single‐phase DGs, it is difficult to regulate the three‐phase voltage within the allowable range and to compensate the unbalance voltage. The aim of this study is to develop the method to supply three‐phase balanced voltage by single‐phase generators in the IDN. First, the operating condition of the generators is proposed for the supply of three‐phase balanced voltage in the IDN model by algebra calculation. The control method for three single‐phase generators has been developed by using the conditions obtained from the derivation of the generators conditions.     

A study of centralized voltage profile control of distribution network considering dynamics of distributed generator

In a future distribution network, it will be difficult to maintain system voltage because a large number of distributed generators are introduced into the system. The authors have previously proposed a voltage profile control method using power factor control of distributed generators. When all information on the system is available, an ideal stationary solution of control orders to distributed generators is given by an optimization calculation. However, it is difficult to apply optimization control in real time because a long calculation time is required for the optimization. Therefore, it is possible that a voltage change may occur before the power factor control has finished. Thus, in this paper, we develop a new control method which can save the excessive voltage changes by taking into consideration the controlled response time of distributed generators. The proposed method was tested in a 24‐node distribution network model. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(1): 29–39, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21231     

Application of unified voltage analysis for high‐ and low‐voltage distribution systems by power flow calculation using indication method between nodes

It has been noted that the voltage of connection points rises according to the reverse power flow when grid‐connected photovoltaic systems are concentrated in distribution systems in residential areas. When this happens, the photovoltaic system may control the power generation output to maintain a suitable voltage for the connection point. Designing a demand area power system aiming at free access to a distributed power supply for energy‐effective practical use requires a precise understanding of this problem. When analyzing photovoltaic systems mainly connected to low‐voltage systems, we looked for a method of analysis in which the high‐voltage systems and the low‐voltage single‐phase three‐wire systems are unified. This report concerns use of the indication method between nodes using power flow calculation, for the purpose of developing a technique of analyzing unified high‐voltage systems and low‐voltage single‐phase three‐wire systems. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(3): 49–62, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10255     

Maximum output power control system of variable‐speed small wind generators

This paper proposes a maximum output power control system for variable‐speed small wind generators. The proposed control system adjusts the rotational speed of a single‐phase AC generator to the optimum rotational speed, which yields the maximum output power according to the natural wind speed. Since this adjustment is performed on‐line in order to adapt to variations in wind speed, the rotational speed of the single‐phase AC generator is adjusted by controlling the generated current flowing in an FET (field‐effect transistor) device, serving as the generated power brake, which is linked directly to the single‐phase AC generator. In order to reduce heat loss from the FET device, a PWM (pulse width modulation) controller is introduced. An experimental model of the proposed control system was built and tested, and the validity and practicality of the proposed control system were confirmed by the experimental results. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(1): 9–17, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20692     

A study of autonomous reactive power control method for distributed power generators to maintain power quality of the grid

Distributed power generators, such as cogenerators and renewable energy systems, have continued to advance and their penetration capacity is increasing. However, they may cause power quality problems in voltage regulation because of the reverse power flow. At present, when the distribution line voltage exceeds the limit value, distributed generators control reactive power to reduce the voltage, and if the reactive power output is not enough, they reduce the active power output. Therefore, an imbalance of active power output between distributed generators may occur because the voltage of generators varies by location and generators at lower voltage locations do not control the reactive power. A power control method for distributed generators needs to be established to solve these problems. In this study, an autonomous reactive power control method of sharing reactive power between distributed generators is proposed. The availability of this method is discussed experimentally and its applicability area is considered analytically by use of a model distribution system. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A study on cooperative tap control method for voltage profile maintenance in distribution networks with distributed generators

The introduction of distributed generators (DGs) that can utilize renewable energy is of prime importance to solve the energy and environmental issues. When a distribution network has a large number of DGs, voltage maintenance becomes a serious problem. To solve this problem, we had proposed the ‘voltage profile control method’ using reactive power control of DGs. However, the control is limited to continuous reactive power control so far, and tap control has not been considered. It is important that the conventional voltage control equipment such as the load ratio tap changer (LRT) or step voltage regulator (SVR) is utilized in order to enhance the control efficiency of the voltage profile control method. Therefore, in this paper, we develop a new method that can realize a cooperative work between inverters and tap control of LRT and SVR. The proposed method is tested in 8‐ and 24‐node model systems and its effectiveness is shown. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Voltage control of distribution network with a large penetration of photovoltaic generation using FACTS devices

In recent years, there has been a great deal of interest in distributed generation from viewpoints of environmental problems and energy saving measures. Thus, a lot of distributed generators will be connected to the distribution network in the future. However, increase of distributed generators, which convert natural energy into electric energy, raises concerns as to their adverse effects on the distribution network. Therefore, control of distribution networks using Flexible AC Transmission System (FACTS) devices is considered in order to adjust the voltage profile, and as a result more distributed generations can be installed into the networks. In this paper, four types of FACTS devices— Static Synchronous Compensator (STATCOM), Static Synchronous Series Compensator (SSSC), Unified Power Flow Controller (UPFC) and self‐commutated Back‐To‐Back converter (BTB)— are analyzed by comparison of required minimum capacity of the inverters in a residential distribution network with a large penetration of photovoltaic generations. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(3): 16– 28, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20499     

Fully distributed tracking control for non‐identical multi‐agent systems with matching uncertainty

This article addresses the fully distributed consensus tracking control problem of linear multi‐agent systems with parameter uncertainties. First, a new class of distributed protocol, based on the relative states of neighbors, is proposed. Theoretical analysis indicates that the considered problem can be solved if the control gain constant of the protocol is larger than the norm bound of the leader's nonlinear inputs. Furthermore, a distributed adaptive control protocol is proposed for the case without available global information. The distributed consensus tracking control problem of uncertain linear multi‐agent systems is solved based only on local information under the proposed adaptive protocol. Finally, an application in low‐Earth‐orbit satellite formation flying is provided to illustrate the theoretical results. Copyright © 2014 John Wiley & Sons, Ltd.     

基于多Agent的二级电压控制系统实现及性能分析

以基于多Agent的二级电压控制系统的基本原理为基础,提出了基于多Agent的二级电压控制系统的实现方案.根据Agent理论模型和电力系统二级电压控制的要求,设计了控制系统中电压控制Agent的各模块并提出了多个控制Agent之间通信、协调和协作的具体实现方法,分析了控制系统在电力系统正常情况下和紧急情况下的运行性能和特点.最后用经典的新英格兰系统进行了数字仿真,仿真结果表明了文中所提设计方案的有效性.     

Zero‐voltage switching modular equalization system for series super‐capacitor string

This paper presents a zero‐voltage‐switching modular equalization for series super‐capacitor string in a large energy storage system. The zero‐voltage working scheme is analyzed based on Power Simulation (PSIM) to verify its validity. An equalization system test for 16‐super‐capacitor cells is conducted under voltage‐imbalanced conditions. The power flow model, switching patterns, and zero‐voltage gap are discussed. The simulation and experimental results are presented, indicating that the equalization not only inherits the advantages of traditional inductor‐based super‐capacitor equalization system, but also brings some merits, such as flexible, low switching loss, and highly modularized.     

Multiple roles coordinated control of battery storage units in a large‐scale island microgrid application

In order to build a large‐scale island microgrid with 100% penetration intermittent photovoltaic power generation as the only power source, a structure with multiple role battery energy storage systems (BESSs) is proposed in this paper based on the analysis of energy storage demand in the island microgrid and performance comparison of two types of batteries. The storage system in the proposed structure is composed of three types of functional BESSs. In detail, the master control units (MCUs) with LiFePO4 batteries are responsible for the voltage and frequency stability and instantaneous power balance, slave storage units (SSUs) with lead‐acid batteries are responsible for daily energy storage, and multi‐function units (MFUs) with LiFePO4 batteries are used for short‐time energy regulation. A hierarchical control structure is adopted in the system. At the local level, the converters of the MCUs are controlled as the voltage sources in paralleled mode as grid‐forming units, and those of SSUs and MFUs are controlled in the current source mode as grid‐feeding units. At the system level, a real‐time power balance coordinated control strategy is proposed, which has the capability of efficient and orderly operation of different types of BESSs. Simulation and practical operation analysis of the Qumalai 7.023 MW microgrid demonstrate the practicality and effectiveness of the research methods of the island microgrid. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A new variable‐speed,constant‐frequency,stand‐alone power generating system

Variable‐speed and constant‐frequency power generating systems using rotor excitation of the wound‐rotor induction machines have been used for such applications as variable‐speed pump generators and flywheel energy storage systems. However, the stand‐alone generating system of this type has only been reported and has not yet been practically used. On the other hand, the stand‐alone generating systems using diesel engines have been widely used for emergency supplies of plants or isolated islands and so on. However, in these cases, synchronous generators are usually used. If the output frequency is to be kept constant, there is the need to control the speed of the engine using a high‐performance governor. Even then, the output frequency changes in the case of a sudden load change. This paper proposes a new stand‐alone power generating system. In this system, the constant‐frequency output voltage can be obtained even though rotor speed changes by several percent. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(2): 75–85, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10191     

Study of Low‐Voltage Ride‐Through Performance for Wind Power Generation with Doubly Fed Induction Generator

The introduction of wind power generation is increasing rapidly. The ratio of wind power generation to the total generation capacity is becoming higher and higher. When a phase‐to‐phase fault occurs in the power system, the frequency of the power system is lower due to disconnection of wind power generation with doubly fed induction generators (DFIG). Therefore, the power system might become unstable. This paper describes an LVRT (low‐voltage ride‐through) performance improvement scheme for wind power generation with DFIG. The wind power generator is disconnected from the grid in case of a power system fault. It is made to operate in isolation from the grid by controlling the inverters installed with the generators. After clearance of the power system fault, wind power generation is immediately reconnected to the grid. As a result, instability in the power system disappears. The performance of LVRT is confirmed by using the simulation software PSCAD/EMTDC. The simulation results show excellent results for the three‐phase short‐circuit fault with a voltage dip of 100%. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 185(1): 17–26, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22423     

基于多Agent的二级电压控制系统

介绍了基于多Agent系统（MAS ）的分层分布式控制系统基本原理，提出了基于多Agent的二级电压控制系统的结构、功能 、特点和实现技术方案。该方案较好地解决了二级电压控制中存在的问题，在正常和紧急情况下都能较好地进行无功电压的协调控制，维持系统的电压水平。用经典的3机9节点电力系 统进行数字仿真，结果验证了该控制方案的有效性。     

A novel multi‐output high‐voltage‐isolated power supply system for semiconductor device series‐connected switches

This paper presents a novel scheme of a multi‐output power supply for solid‐state switches based on series‐connected semiconductor devices. By using the loosely transforming method, the system can realize high‐voltage isolation and a compact size, and its application range can be easily expanded to modular designed switch stacks for higher power ratings. The circuit structure and working principles are described. Based on the system operating equations, the design methodology is proposed and applied for parameter specification of a power supply system of two series‐connected switch stacks containing 20 outputs. Detailed calculations are given, and experimental results prove the feasibility of the proposed scheme. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Decentralized model predictive‐based load‐frequency control in an interconnected power system concerning wind turbines

This paper presents a load‐frequency control (LFC) design using the model predictive control (MPC) technique in a multi‐area power system in the presence of wind turbines (WTs). In the studied system, the controller of each local area is designed independently such that the stability of the overall closed‐loop system is guaranteed. A frequency response model of the multi‐area power system including WTs is introduced, and physical constraints of the governors and turbines are considered. The model was employed in the MPC structures. Digital simulations for a two‐area power system are provided to validate the effectiveness of the proposed scheme. The results show that with the proposed MPC technique the overall closed‐loop system performance shows robustness in the face of uncertainties due to governor and turbine parameter variation and load disturbances. A performance comparison between the proposed controller with WTs and MPC without WTs and a classical integral control scheme is carried out, confirming the superiority of the proposed MPC technique with WTs. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.