Configuration of a voltage sag compensator by use of a micro‐SMES and experimental results

A voltage sag compensating using a micro‐SMES is presented. Based on previous works, we have carried out experiments for voltage sag compensation on the laboratory‐built system in order to validate the proposed minimum energy injection voltage sag compensation algorithm. To improve the compensating performance of the system, two‐degree‐of‐freedom voltage control is proposed. In this paper, the circuit configuration and feedback voltage control system of the compensator are described and the experimental results are reported. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 84–92, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10267     

Voltage sag compensation strategy for unified power quality conditioner with simultaneous reactive power injection

Unified power quality conditioner（UPQC）holds the capability of solving power quality problems,especially shows good performance in the voltage sag compensation. In this paper, a compensation strategy based on simultaneous reactive power injection for UPQC（namely UPQC-SRI） is proposed to address the issue of voltage sag. The proposed UPQC-SRI determines the injection angle of compensation voltage with consideration of optimal configuration of UPQC current-carrying.Moreover, the compensation strategy also considers the current-carrying limit of UPQC, and then the zero active power injection region of UPQC-SRI（also called UPQCSRI region） is obtained. Under the conditions which exceed the UPQC-SRI region, the limit value of shunt current is determined by this proposed strategy. Finally, the proposed strategy and the corresponding algorithm are verified under the PSCAD/EMTDC platform. The result indicates the proposed UPQC-SRI strategy in this paper can provide more persistent voltage sag compensation than the previous strategies for the sensitive load.     

Dynamic voltage restoration with minimum energy injection

Voltage sag is one of the most important power quality problems challenging the utility industry. Voltage sags can be compensated for by voltage and power injection into the distribution system. By injecting voltage with a phase advance with respect to the sustained source-side voltage, reactive power can be utilized to help voltage restoration. Hence, the consumption of real power, from the perspective of the energy supply device, can be reduced. This energy-saving voltage injection comes at the expense of an increased voltage injection magnitude, load power swing, phase shift, and discontinuity of voltage wave-shape. For this reason, several proposed compensation strategies are examined, in terms of satisfying custom power while taking into consideration the capacity of the energy-storage device and the voltage injection constraint of dynamic voltage restorer. Numerical examples are included to illustrate the efficacy of the proposed control strategies     

Modeling and analysis of a flywheel energy storage system for Voltage sag correction

The U.S. Navy is looking for methods to maximize the survivability of combat ships during battle conditions. A shipboard power distribution system is a stiff isolated power system that is vulnerable to voltage sags, which arise due to faults or pulsed loads, which can cause interruptions of critical loads. A series voltage injection type flywheel energy storage system (FESS) is used to mitigate voltage sags and maximize the survivability of the ship. The basic circuit consists of an energy storage system, power electronic interface, and a series injection transformer. In this case, the energy storage system consists of a flywheel coupled to an induction machine. The stored energy is used for sag correction for the critical load. Indirect field-oriented control (IDFOC) with space-vector pulsewidth modulation (SVPWM) is used to control the induction machine. Sinusoidal PWM is used for controlling the power system side converter. This paper presents the modeling, simulation, and analysis of a FESS with a power converter interface using PSCAD/EMTDC.     

电压源型SMES功率调节特性研究

在论述电压源型SMES(VSMES) 调节输出功率的机理的基础上,利用MATLAB 建立了VSMES 的时域仿真模型,利用所建立的模型,分别对VSMES 的有功功率、无功功率及有功和无功同时独立四象限调节特性进行了仿真研究,所得的结论为VSMES 的建模、运行、设计和系统参数的选择提供了依据。     

Evaluation of the introduction of a micro‐cogeneration system into residential houses based on monitored daily‐basis energy demand data

In order to reduce CO₂ emission from residential sectors in Japan, PEFC with high efficiency and low environmental impact is expected as one of the promising micro‐cogeneration (µCGS) systems. However, the energy demands in houses largely differ from each other and the profiles are also changed every day. Thus, when µCGS is actually introduced, it is necessary to examine the equipment capacity and operation of µCGS in each house. In this paper, the optimization model is developed in order to evaluate the µCGS based on daily‐basis demand data. Using actually monitored energy demand data in four households, the differences between using daily‐basis data and using the monthly‐average data are evaluated from viewpoints of economic and environmental performance of µCGS systems. Moreover, by adding the penalty factor to disposal heat of µCGS, it is seen that system configuration and system operation of µCGS can attain CO₂ reduction and energy conservation as well as cost reduction. ©2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(4): 20–30, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20653     

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     

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     

励磁与SMES协调控制中的静态偏移问题

针对汽轮发电机励磁与SM ES线性最优协调控制设计时出现的发电机端电压静态偏移问题,采用了积分线性最优控制设计方法。仿真表明:该控制规律能够很好地兼顾系统各状态量的动、静态特性,消除了发电机端电压的静态偏移,提高了系统的稳定运行能力。     

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     

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     

Fabrication of flat micro‐gap electrodes for molecular electronics

Recently, organic molecular electronic devices such as molecular thin‐film transistors have received considerable attention as possible candidates for next‐generation electronic and optical devices. This paper reports on fabrication technologies of flat metallic electrodes on insulating substrates with a micrometer separation for high‐performance molecular device evaluation. The key technologies of fabricating planar‐type electrodes are the liftoff method by the combination of bilayer photoresist with overhang profile, electron beam evaporation of thin metal (Ti and Au) films, and SiO₂‐CMP (Chemical Mechanical Polishing) method of CVD (Chemical Vapor Deposition)‐deposited TEOS (tetraethoxysilane)–SiO₂ layer. The raggedness of the electrode/insulator interface and the electrode surface of the micro‐gap electrodes were less than 3 nm. The isolation characteristics of fabricated electrodes were on the order of 10¹³ ohms at room temperature, which is sufficient for evaluating electronic properties of organic thin‐film devices. Finally, pentacene FET (Field Effect Transistor) characteristics are discussed fabricated on the micro‐gap flat electrodes. The mobility of this FET was 0.015 cm²/Vs, which was almost on the order of the previous results. These results suggest that high‐performance organic thin‐film transistors can be realized on these advanced electrode structures. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(2): 39–46, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20152     

用麦也尔电弧模型分析雷击引起的电压凹陷

雷击是当前电力系统面临的最严重的事故和故障原因。雷击在电力系统中产生过电压,该过电压如果超过电气设备的绝缘水平,就会导致系统故障,因此研究雷击引起的电压凹陷对于实际电力系统具有重要的理论价值和现实意义。侧重探讨配电网络由雷击引起的几种电压凹陷,即雷击引起的绝缘子闪络、保护间隙击穿续流、电弧接地引起的电压凹陷。由于电弧现象的复杂性,使得在以往的数字仿真中,仅仅用理想短路或者一个线性电阻来模拟接地故障电弧,大大降低了仿真结果的可信度。为解决这个问题,依据麦也尔电弧数学模型,给出了接地故障电弧的精确数字仿真模型。     

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     

Performance of a power conversion system for superconductingmagnetic energy storage (SMES)

This paper presents the results of laboratory tests of a power conversion system (PCS) for superconducting magnetic energy storage (SMES) applications. The PCS uses a two-quadrant chopper and a voltage-source power converter. Operating modes of the chopper are discussed. Operation of SMES to provide independent control of real and reactive power, operation as a static VAr compensator, low frequency modulation of the real power and speed of response are demonstrated. A circuit is presented for testing an SMES PCS that does not require a superconducting coil     

Determination of loss‐minimum configuration with mathematical optimality in a three‐sectionalized three connected distribution feeder network

In a distribution system, in order to enhance the reliability of power supply, the distribution feeder is divided into several sections by installing sectionalizing switches, and then each of the sectionalized sections is connected to a different feeder. For example, one feeder is divided into three sections by two sectionalizing switches, and then each of the divided sections is connected to the other feeder through sectionalizing switch. Since a distribution system with many feeders has many sectionalizing switches, the system configuration is determined by states (opened or closed) of sectionalizing switches. Usually, a power utility tries to obtain distribution loss‐minimum configuration among large numbers of configuration candidates. However, it is very difficult to determine the loss‐minimum configuration such that the mathematical optimality is guaranteed, because it is well known that determination of a distribution system's configuration is to decide whether each sectionalizing switch is opened or closed by solving a combinatorial optimization problem. In this paper, the authors propose a determination method of loss‐minimum configuration by which the mathematical optimality is guaranteed for a three‐sectionalized three‐connected distribution feeder network. A problem to determine the loss‐minimum configuration is formulated as a combinatorial optimization problems with four operational constraints ( feeder capacity, voltage limit, radial structure, and three‐sectionalization). In the proposed method, after picking up all partial configurations satisfied with radial structure constraint by using enumeration method, optimal combination of partial configurations is determined under the other operational constraints by using conventional optimization method. Numerical simulations are carried out for a distribution network model with 140 sectionalizing switches in order to examine the validity of the proposed algorithm in comparison with one of conventional meta‐heuristics (tabu search). © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(1): 56– 65, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20530     

Economic evaluation of demand‐side energy storage systems by using a multi‐agent‐based electricity market

With the wholesale electric power market opened in April 2005, deregulation of the electric power industry in Japan has faced a new competitive environment. In the new environment, Independent Power Producer (IPP), Power Producer and Supplier (PPS), Load Service Entity (LSE), and electric utility can trade electric energy through both bilateral contracts and single‐price auction at the electricity market. In general, the market clearing price (MCP) is largely changed by the amount of total load demand in the market. The influence may cause a price spike, and consequently the volatility of MCP will make LSEs and their customers face a risk of higher revenue and cost. DSM is attractive as a means of load leveling, and has an effect on decreasing MCP at peak load period. Introducing Energy Storage systems (ES) is one DSM in order to change demand profile at the customer side. In the case that customers decrease their own demand due to increased MCP, a bidding strategy of generating companies may be changed. As a result, MCP is changed through such complex mechanism. In this paper the authors evaluate MCP by multi‐agent. It is considered that customer‐side ES has an effect on MCP fluctuation. Through numerical examples, this paper evaluates the influence on MCP by controlling customer‐side ES corresponding to variation of MCP. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(3): 36–45, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20658     

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     

Decoupling control with a limiting form of linear optimal regulator for a non‐minimum phase system

In this paper, a decoupling control for a non‐minimum phase system is considered in terms of the limiting form of linear optimal regulator problems, and an explicit relationship between the limiting properties and the decoupling control is shown. Moreover, using an appropriate performance index, this paper deals with a new method of decoupling control to exclude the effect of the fixed poles by pole‐zero cancellation. Stability and sensitivity are improved by this method. This paper also gives numerical examples to illustrate the effectiveness of decoupling control with the limiting form. © 2000 Scripta Technica, Electr Eng Jpn, 132(2): 49–57, 2000     

Distributed mitigation of voltage sag by optimal placement of series compensation devices based on stochastic assessment

Central mitigation does not necessarily provide the most economical solution to voltage-sag problems. Distributed mitigation with strategically placed compensation devices should provide a better alternative. Placement studies of this nature usually involve extensive evaluations of candidate compensation schemes, which can become unmanageable for large systems with stochastic voltage-sag data. A probability-based technique known as the weighted sampling method is proposed to simplify the problem. The technique is applied to a distribution system to optimize the cost of placing series compensation. The cost has two components: device cost and cost reduction to consumers due to implementation of the device(s). Series compensation devices being optimized are the two distinctly different dynamic voltage restorer and thyristor voltage regulator. These devices are placed and optimized to best complement each other. To achieve reliable and fast convergence, a genetic algorithm with innovative coding is proposed. A 34-node distribution system is studied with a wide range of voltage-sag data and consumer tolerance characteristics.