Voltage sag compensation with minimum energy injection by use of a micro‐SMES

This paper presents a method to compensate voltage sags with minimum energy injection for a series‐connected voltage restorer using a micro‐SMES. A circuit for extracting the fundamental symmetrical components from sag voltages and a minimum energy injection algorithm is described. Simulations of voltage sag compensation have been carried out using PSCAD/EMTDC for various faults. The simulation results confirm the validity of the proposed method and show the possibility of reducing the size of energy storage devices. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(3): 70–80, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10047     

Control of fault current limiter by series‐connected voltage sag compensator

This paper describes a control scheme of fault current limiter by series voltage injection. The current limiter proposed in this study is based on the use of a SMES‐based series‐connected voltage sag compensator, which has been previously studied by the authors, for controlling fault current caused by short circuit on the load side. An algorithm for fast discriminating between power system voltage sag and load‐side short circuit is proposed for the equipment to correctly function either for voltage sag compensation or for fault current limiting purpose. Furthermore, a new control strategy based on output voltage phase control of the series compensator is proposed for current limiting with good waveform characteristics and low active power absorption. Experimental results demonstrated the validity of the proposed strategy. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(2): 64–72, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20128     

Flywheel size design considerations and experimental verification using a 50‐kW system for voltage sag compensator with flywheel induction motor

Flywheel energy storage systems can be used as an uninterrupted power supply system because they are environmentally friendly and have high durability. The use of a simple voltage sag compensator with a low‐speed heavy flywheel and a low‐cost squirrel‐cage induction motor/generator is proposed. First, the ability of the proposed system to maintain the load voltage at 100% when the grid is experiencing voltage sag is validated experimentally. Next, design guidelines for the flywheel stored energy are discussed. Experimental verification of a 50‐kW‐class system is carried out, and the results show good agreement with the developed design guidelines. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(1): 36–44, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21252     

Effective operation method by interdependent use of condenser energy of the voltage transient sag compensator with controlled gradational voltage

This paper presents the efficient operation method of the interdependent use of condenser energy on the new concept of voltage transient sag compensator. This compensator consists of the series connection inverter units, and each inverter unit generates a different output voltage by 2ⁿ times. The method proposed here, in any case of various levels of transient voltage sags on the power line, provides the efficient use of condenser energy of all these inverter units. The method of interdependent use of condenser energy is also verified by the experiment. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(3): 56–64, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20290     

Development of voltage sag compensator and UPS using a flywheel induction motor and an engine generator

Flywheel energy storage systems are attracting attention as uninterruptible power supplies (UPS) from the viewpoint of environmental friendliness and high durability performance. Using a low‐speed, heavy flywheel and a low‐cost squirrel‐cage induction motor/generator, two applications are proposed: (1) an 11‐kW voltage sag compensator using a capacitor self‐excited induction generator without semiconductor converters and (2) a UPS composed of the flywheel system and an engine generator. Based on experimental results, an ideal voltage sag compensator and UPS are realized by the low‐technology flywheel system. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(1): 74– 81, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20784     

Interior structure of a quality control center at the low‐voltage side considering power conditioning by SMES

The authors have proposed FRIENDS—Flexible, Reliable and Intelligent Electrical eNergy Delivery System—as a future electric power distribution system. The most important idea of FRIENDS is to install new facilities called Quality Control Centers (QCCs) between the distribution substation and customers. By controlling QCCs appropriately, various purposes of FRIENDS can be achieved. It is indispensable to design the concrete interior structure of QCC in order to realize FRIENDS. This paper proposes the interior structure and control methods of QCC from the viewpoint of power conditioning functions by energy storage system in QCC. In this paper, it is assumed that SMES is used as the energy storage system in QCC. The proposed interior structure is based on the concept of UPS (Uninterruptable Power Supply). In this paper, SMES is installed in the DC side of UPS. Further, this paper proposes control methods of SMES and PWM converters. The proposed control methods are used to satisfy various purposes, such as load fluctuation compensation, load leveling, and cooperation with dispersed‐type generator. Finally, the validity of these control methods is confirmed through transient analysis PSCAD/EMTDC. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(3): 20–28, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10056     

有功注入型电压质量补偿器控制策略及仿真研究

为了解决对电压质量问题长时间补偿和复合补偿的需求,提出了一种有功注入型电压质量补偿装置。利用PWM整流器为装置直流母线提供电压支撑,使装置能够实现对长时间的电压质量扰动的有效补偿。采用基于瞬时无功理论的算法对电压质量扰动进行检测,采用了基于最小电压注入法的补偿策略和分段补偿逻辑,提出了复合电压质量补偿控制策略,能够实现对电压暂降、暂升、谐波和欠电压等电压扰动的多目标补偿。在PSCAD/EMTDC中,对所提主电路拓扑和补偿控制策略进行了仿真分析和验证。仿真结果表明,所提装置能够对电压质量问题进行长时间补偿和复合补偿,主电路拓扑和补偿控制策略可行有效。     

Development of a voltage sag detection method for nonutility generation systems

This paper deals with a new detection method based on three‐phase vector operation for voltage sag. The detection method is applicable to a protection system using a high‐speed interruption system which protects distributed generators and critical loads in a customer's facility. The algorithm and merits of this method are explained in detail. The detection characteristics are then analyzed using the ATP (Alternative Transients Program) and are confirmed using a real‐time digital simulator, and it is shown that the method is useful for detecting voltage sag. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(4): 34–41, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20117     

A design method of a generalized predictive control system based on parametrization of two‐degree‐of‐freedom integral controllers

A new design method for a generalized predictive control (GPC) system based on parametrization of two‐degree‐of‐freedom integral controllers has been proposed. The objective is to guarantee stability of the control system without depending on the design parameters and to achieve low sensitivity against the plant perturbation and the disturbance. The design procedure consists of two steps. First, we design a basic integral controller for a nominal plant using the linear quadratic Gaussian (LQG) method and parametrize a class of two‐degree‐of‐freedom stabilizing controllers. Next, we tune the feedforward controller to incorporate the GPC method into our control structure. A numerical example is presented to show the effectiveness of the proposed method by comparing it with the conventional GPC method. © 1999 Scripta Technica, Electr Eng Jpn, 129(2): 62–70, 1999     

Parallel voltage sag compensator with reduced capacitance using a boost‐type power factor correction rectifier

A new circuit of parallel‐type voltage sag compensator is proposed in this paper. The proposed voltage sag compensator can reduce the necessary capacity of the energy storage capacitor for compensation by boost‐type power factor correction rectifier charging the capacitor during a voltage sag. As a result the proposed system can reduce the size and maintenance of the apparatus. Copyright © 2004 Wiley Periodicals, Inc. This paper shows the principle and control system of the proposed circuit. Compensation characteristics were demonstrated by simulation and experiment. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(2): 19–33, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20261     

Two‐degree‐of‐freedom model matching control of shift‐by‐wire system with emergency mechanical link

A new shift‐by‐wire system having a standby mechanical link with backlash is proposed. The link directly connects the select lever and the manual lever of the automatic transmission in case of emergency. Thus, it is necessary to keep the backlash free during normal operations without generating a force. The angles of the manual lever driven by an actuator should follow the angles of the select lever exactly and quickly. A two‐degree‐of‐freedom model matching control is developed to meet this requirement. It is shown that the backlash is kept free during the range select operation. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(3): 45–52, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21049     

Design of a robust PWM power amplifier using approximate two‐degree‐of‐freedom integral‐type control

A method is proposed for designing a robust controller for PWM power amplifiers, which are widely used as amplifiers and power supplies. The main technical requirements imposed on PWM power amplifiers are linearity in a wide frequency range and a well‐damped fast dynamic response in the presence of extensive load and DC power supply variations. Therefore, in order to satisfy the design specifications, namely, linearity in a wide frequency range and no overshoots during transients, an approximate two‐degree‐of‐freedom integral control structure is proposed and a design procedure for the robust controller is discussed. It is shown by some simulations and experiments that the designed controller shows especially good dynamic performance and effective disturbance rejection in the presence of external disturbances, that is, load and power‐supply variations. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(1): 68–77, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10102     

一种改进不完全S变换的电压暂降检测方法

为实现对电压暂降的准确快速检测,提出了一种改进不完全S变换(MIST)的电压暂降检测方法。该方法对从电网中采集到的电压信号进行快速傅里叶变换,获得信号的主要频率点;对各主频点进行改进的S变换,获得信号主频特征分量;利用这些特征分量信息实现对电压暂降扰动特征量的检测。首先描述了改进不完全S变换的原理及其参数选择的原则,然后详细叙述了电压暂降特征量的提取方法,最后对实际信号进行了仿真。仿真结果表明,该方法可有效地提取电压暂降的幅值、持续时间、相位跳变等特征信息,并且准确率高,运算量小,同时具有一定的抗干扰能力。     

A study of decoupling with skeleton matrix in two‐degree‐of‐freedom generalized minimum variance control

There are many multi‐input multi‐output (MIMO) systems in chemical plants, and they have multiple time delays of different length in each input and output pair. This paper explains a two‐degree‐of‐freedom (2DOF) control system based on generalized minimum variance control (GMVC) for MIMO systems. It can improve the tracking performance with respect to the reference signals and the response properties for the disturbance. The states between the sampling period can be expressed by using the modified z transform to take account of multiple time delays. Additionally, a tracking controller is designed to decouple the plant. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(1): 28–36, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21046     

Design and implementation of a high‐efficiency bidirectional DC‐DC Converter for DC micro‐grid system applications

This paper studies the design and implementation of a non‐isolated dual‐half‐bridge bidirectional DC‐DC converter for DC micro‐grid system applications. High efficiency can be achieved under wide‐range load variations by the zero‐voltage‐switching features and an adaptive phase‐shift control method. A three‐stage charging scheme is designed to meet the fast‐charging demand and prolong the lifetime of LiFePO₄ batteries. A digital‐signal‐processing control IC is used to realize the power flow control, DC‐bus voltage regulation, and battery charging/ discharging of the studied bidirectional DC‐DC converter. Finally, a 10 kW prototype converter with Enhanced Controller Area Network communication function is built and tested for micro‐grid system applications. A light‐load efficiency over 96% and a rated‐load efficiency over 98% can be achieved. Copyright © 2013 John Wiley & Sons, Ltd.     

电网结构对电压暂降传播的影响及其量化分析方法

有效的电压暂降治理方法对减少用户经济损失起着重要的作用。现有电压暂降治理方法基于随机预估等方式获取电网各节点的电压暂降水平,从而针对暂降严重的节点进行治理,但这些方法仅能量化暂降水平的大小,难以分析造成暂降严重的根本原因,治理效果亟待提高。其本质原因在于忽视了电压暂降在电网中的传播规律和电网结构对电压暂降的影响机制。为此,对电压暂降受电网结构属性的影响进行分析并对其量化方法开展研究。首先,基于电网故障模型分析电压暂降幅值与电网结构的关系,并将监测周期内多次故障下电网所有节点电压平均幅值构成的序列定义为电压暂降模式,以挖掘电压暂降受电网结构属性的影响;然后,通过分析电压暂降的传播特性,从电网拓扑属性和物理属性出发提出电压暂降结构性指标,从电网节点规模程度、聚集程度、传播效率和支撑能力等不同的方面量化电网结构对电压暂降的影响;最后,提出电压暂降受电网结构影响程度的综合评估方法,为电网侧电压暂降治理提供决策支持。基于IEEE 30节点系统的仿真结果验证了所提方法能够反映电网结构对电压暂降的影响规律,以敏感用户接入电网的规划为例,验证了所提结构指标有助于从电网侧治理电压暂降问题,并能够对优质供电园区的电网规划与重构、电网运行方式反演、电压暂降传播途径抑制等措施提供决策支持。     

Application of a dispersed autonomous voltage control system to a real high‐voltage distribution network

This paper focuses on the application results of the dispersed autonomous voltage control system, which the authors have proposed, to a real distribution network. This system is effective for regulating the supply voltage of an entire HV line within an optimum range. In the system configuration, an SCC is installed together with an SC and/or ShR on the line. Individual SCCs autonomously control the operation of SCs and/or ShRs based on the voltage measured where the SCs and/or ShRs are located on the line. A field test on a real high‐voltage distribution network found that the proposed system could sustain a high fault tolerance ability and also be cost‐effective in regulating line voltage. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(1): 27–36, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10252     

Studies on steady‐state stability of looped power systems and stabilization by SMES

With the increasing number of dispersed power sources interconnected to the power supply system, power systems can take a form similar to that of a longitudinal system. Also, they can become looped, with both ends of the longitudinal system connected to each other. In the present paper, the steady‐state stability of longitudinal power systems and looped power systems is analyzed by means of the mode analysis method via eigenvalue and eigenvector calculation, and power system stabilization by SMES (Superconducting Magnetic Energy Storage) for looped systems is examined relative to that for longitudinal systems. © 2000 Scripta Technica, Electr Eng Jpn, 133(3): 48–54, 2000     

A fuzzy logic‐controlled SMES for damping shaft torsional oscillations of synchronous generator

This paper presents a fuzzy logic control scheme for the superconducting magnetic energy storage (SMES) based on a PWM voltage source converter and a two‐quadrant chopper using an insulated‐gate‐bipolar‐transistor (IGBT) to dampen turbine‐generator shaft torsional oscillations. Simulation results of balanced faults in a single machine connected to an infinite bus system show that the proposed fuzzy logic‐controlled SMES is effective in damping shaft torsional oscillations of synchronous generators (GENs). © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Improvement of Dynamic Stability in a Multimachine Power System via SMES with Active Power Modulation Controlled by Frequency Deviation

With the recent increase in demand, power systems have become large and complex and generation plants are located far from the load center. As a result, power system instability has become more serious. On the other hand, the active and reactive powers am controlled rapidly and flexibly by the superconducting magnetic energy storage (SMES) system. This paper proposes a practical method to suppress power oscillation in a multimachine power system by using SMES wherein its active power is controlled by the signal derived from a bus frequency deviation. This controlled scheme is conducted easily only by detecting the frequency deviation on the site. The proposed method is examined on a 4-machine miniature power system connecting a I-MJ SMES as well as another digital simulation using the same model. The effectiveness of the proposed method is shown.