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Abstract: For size reduction of gas insulated switchgears (GIS), application of permittivity‐graded material to insulating spacer has been studied. The electric‐field‐enhancement close to the lamination interface of the permittivity‐graded material obtained by laminating epoxy composites with different permittivities was investigated. The FEM simulation revealed that the increase of the layer number of the permittivity‐graded material could reduce the field enhancement close by the lamination interface, even when considering electric field distortion near the individual high‐permittivity particles filled in each layer. [ABSTRACT FROM AUTHOR]

In this study, the three‐phase four‐wire shunt active power filter (ShAPF) dealing with non‐ideal point of common coupling (PCC) voltages will be presented. The instantaneous power theory is applied to design the ShAPF controller which shows reliable performances. An adaptive notch filter (ANF) is proposed to process those unbalanced and/or distorted PCC voltage. The power balance among utility, load and ShAPF while applying ANF is clarified by an in‐depth explanation. The simulation results prove that the ANF can successfully facilitate the ShAPF in terms of compensating unbalanced/distorted current of loads under a non‐ideal PCC voltage circumstance. [ABSTRACT FROM AUTHOR]

In the dispersed generation (DG) field, islanding is known as a situation in which those generators are disconnected from the utility feeders and a bunch of local loads being powered by them is isolated. Accordingly, anti-islanding schemes are used to immediately detect the phenomenon in facilitating the detachment of the DG or adaptively controlling the autonomous operation. Negative-sequence impedance measurement is considered as a novel method of detecting electrical islands in DG networks. However, in the case of high induction motor penetration, this method might malfunction. Using two-round impedance measurement, this paper deals with that problem while making typical assessments on how the impedance tolerance values are selected and how these values vary with network configuration. The simulation in PSCAD/EMTDC and experiments validate the methodology. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

A grid-connected inverter offers good operation and controllability; however, there is a risk of local instabilities due to particular control schemes. As long as the input admittance is positive at a particular resonance frequency, the risk of local instability can be suppressed. In this paper, an attempt to improve the input admittance of the grid-connected inverter (GCI)[vnsn1] using a virtual resistor is proposed. The impact of the virtual resistor on the inverter's passivity is analyzed by observing the input admittance of the inverter. Numerical analysis shows that the employment of the virtual resistor gives better input admittance to the GCI, particularly in the low-frequency regions. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

This paper presents an efficient strategy to solve the thermal economic load dispatch (ELD) problem by considering several aspects of ELD. ELD performs an important role in the economical operation of power system, which essentially involves nonlinearity according to the characteristics of the generators. The complexity is amplified when the generators' prohibited zones and valve-point effect are considered, which makes ELD a nonconvex and nonsmooth problem. The strategy employs a mechanism involving a quantum mechanics-inspired particle swarm optimization (QMPSO). The conventional PSO is modified by integrating quantum mechanical theory which redefines the particles' positions and velocities in a dynamic manner and therefore explores more search space. The QMPSO employs a multipopulation-based scheme which ensures particle movement and avoids premature convergence at the same time. Moreover, in order to diversify the particles, a dynamic mutation operator is introduced in the proposed method. Such features deliver a fine balance between the local and global searching abilities. Simulations are carried out by considering several cases of thermal units of varying combinations of system configurations such as with and without the valve point, with and without network loss, and for one or several hours of load demand. The results are quite promising and effective compared with several benchmark methods. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

This paper presents a fuzzy-logic-based binary particle swarm optimization (BPSO) method for solving short-term thermal unit commitment problem integrated with an equivalent wind-battery system. As a renewable power source, wind power is injected stochastically with the model. To handle the uncertainty and intermittency due to the wind power integration, the trivial crisp problem formulations are modified by introducing fuzzy logic. Moreover, since it is also forecast, load demand along with the spinning reserve and production cost are taken under fuzzification. The potential solutions are distributed among several clusters based on a clustering scheme which exploits their associated fitness values. The fitness value is functionalized by combining the objective function, penalty function, and the aggregated fuzzy membership function. After clustering, each solution is updated according to the velocity and position BPSO refinement functions. The clustering scheme inherently introduces multipopulation-based search space exploration in PSO. Therefore, this algorithm allows the particles to explore a larger search space in the problem domain by diversification of particles. Simulation results are provided to show the effectiveness of the proposed method by scrutinizing two different power systems. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

Wind power generation using an unlimited, natural energy has been getting attention regarding environmental issues in recent years, and the installed capacity of wind power generation system is increasing at a rapid pace, resulting in deterioration of power quality especially in frequency and voltage. This fact will be a big problem in restricting large capacity of wind farms. This paper proposes a new frequency converter: rotary frequency converter (RFC) to moderate the electric output from wind generation, which is to be installed between a set of wind generators and a grid, providing a smoothed electric output, promoting the wind power generation introduction. This mainly consists of a synchronous machine and the adjustable-speed machine. Independent controls of input/output voltage, active power, and reactive power offer electrical separation between the two networks. Experimental study of a prototype model and its characteristics, especially dynamic control, is discussed in this paper. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(4): 26–34, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20922 [ABSTRACT FROM AUTHOR]

Electric utility deregulation enabled PPSs (Power Producers and Suppliers) to enter the electricity market. PPSs are supposed to achieve 30-minute balancing control for stable power supply of electric power. In addition, load rejection and instantaneous voltage drops greatly affect turbine shafting, that is, torsional torque oscillation. Therefore, PPSs must consider a reduction of torsional torque in order to prevent generator shaft damage. This paper proposes a control system which allows the achievement of both 30-minute balancing control and reduction of torsional torque by using an H∞ controller. The effectiveness of the proposed controller is validated by using MATLAB. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(1): 16–25, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20868 [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

This paper deals with two types of control method for induction generators used in wind power generating stations. One is aimed at maintaining the voltage of the station node and the other is aimed at maintaining a constant power factor through the branch connecting to the station. Both can be in the controllable area by adjusting the generator reactive power with compensating capacitors. First, theoretical equations for the terminal voltage and power factor of an induction generator are derived, and then the compensating capacitance corresponding to the wind velocity variation is determined quantitatively. By using the proposed control method, it is shown to be possible to maintain the terminal voltage and operating power factor of a wind power generation system at the target values, even when abrupt deviations are caused by wind power disturbances. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(3): 19– 26, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20298 [ABSTRACT FROM AUTHOR]

This paper presents a method of position sensorless control of ultrasonic motors (USM). The position sensorless control method is useful for reducing the cost and size of drive system. The position estimation method is based on the input voltage information of the ultrasonic motor. The characteristic of input voltage versus rotor position is expressed by a quadratic function which is used to estimate a rotor position based on input voltage information. This estimation method, which uses only the drive voltage of the ultrasonic motor, is a very simple algorithm and shows good estimation ability. The parameters of the quadratic function are adjusted by using the recursive least squares method and are obtained on-line. Since it can correspond to parameter change, the estimated rotor position shows good agreement with the measured rotor position against load torque and motor temperature changes. Sensorless position control is achieved by using the estimated rotor position instead of the measured rotor position. The validity of the proposed method is confirmed by experimental results. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(1): 57–64, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20626 [ABSTRACT FROM AUTHOR]

Wind power generation is expected to become more important in future distribution systems. Although several prospective reports such as IEC 61400-24 and NREL SR-500-31115 indicate an insulation scheme and grounding design for lighting protection, there still seems to be too few investigations on the problems. This paper therefore discusses lightning surge analysis using a wind farm model with 2 or 10 ideal wind turbines. Changing parameters such as grounding resistance and lightning strike points, several cases were studied. As a result of the analysis using digital simulator ARENE, it is clear that the surge tends to propagate toward the end of a distribution line in a wind farm and there is the possibility of insulation accidents at the other wind turbines when lightning attacks a wind turbine. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(2): 30– 38, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20364 [ABSTRACT FROM AUTHOR]

Effective utilization of renewable energies such as wind energy instead of fossil fuels is desirable. Wind energy is not constant and windmill output is proportional to the cube of the wind speed, which causes the generated power of wind turbine generators (WTGs) to fluctuate. In order to reduce the output power fluctuation of wind farms, this paper presents an output power leveling control strategy for a wind farm based on both the average wind farm output power and the standard deviation of the wind farm output power, a cooperative control strategy for WTGs, and pitch angle control using a generalized predictive controller (GPC) in all WTG operating regions. Simulation results using an actual detailed model for wind farm systems show the effectiveness of the proposed method. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 31– 41, 2007; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20448 [ABSTRACT FROM AUTHOR]

We propose a new protection scheme for selective and quick disconnection of a fault area in a distribution system, which can be flexibly adopted for a large-scale introduction of distributed generators (DGs). When a fault occurs, relays provide a binary state signal which is activated if, for instance, the current at the corresponding relay location exceeds a certain value. Although each relay cannot locate the fault point with only its own signal, it can locate the fault by utilizing signals from other relays together with its own signal. Because only a binary state signal is transmitted instead of the actual physical variable such as the magnitude of the fault current, the network traffic is much less than when a conventional protection scheme for a transmission system using an information system is applied to a distribution system. The following are the main results of a simulation on our proposed protection scheme: (1) the proposed protection scheme can successfully disconnect only a fault feeder when the relays use signals provided from the sending end of the fault feeder and all other DGs on the same feeder, (2) in the case of a fault on a DG connected feeder, the DG can be disconnected within 0.06 s. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(4): 30–35, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20232 [ABSTRACT FROM AUTHOR]

Effective utilization of renewable energies such as wind energy as a replacement for fossil fuels is highly desirable. Wind energy is not constant and wind generator output is proportional to the cube of the wind speed, which causes the power output of wind turbine generators (WTGs) to fluctuate. In order to reduce output power fluctuations of wind farms, this paper presents an output power leveling control strategy for wind farms based on both the mean and the standard deviation of wind farm output power, a cooperative control strategy for WTGs, and a pitch angle control method using a generalized predictive controller (GPC) intended for all operating regions of WTGs. Simulation results using an actual detailed model for wind farm systems show the effectiveness of the proposed method. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(2): 10–18, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20247 [ABSTRACT FROM AUTHOR]

The ultrasonic motor has comparatively high nonlinearity which varies with driving conditions, and possesses a variable dead zone in control input associated with the applied load torque. The dead zone is a problem for industrial applications and it is important to eliminate the dead zone in order to improve control performance. This paper proposes a new position control scheme for ultrasonic motors to overcome the dead zone. The dead zone is compensated by fuzzy inference, and backstepping control performs accurate position control. Compared with model reference adaptive control, which uses an augmented error, backstepping control can analyze a transient response. Mathematical models are formulated and experimental results show the effectiveness of the proposed position control scheme. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(1): 69–77, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20016 [ABSTRACT FROM AUTHOR]

Recently, there has been growing interest in utilizing dispersed generation systems, which are grouped into micro turbine systems, co-generation systems, and so on, as a substitute for fuel oil energy and a technology to prevent global warming. Since start-up time of dispersed generation systems is short, it is possible to operate systems to supply load power corresponding to a demand. Moreover, PPSs (Power Producers and Suppliers) can participate in a power retail sales company, since deregulation of electric utilities was instituted in March 2000. However, PPSs have to keep instantaneous generating power commissioning rule, to maintain supply-and-demand balance between customer and supplier. Therefore, in this paper, we examine instantaneous generating power commissioning for dispersed generators where start-up time is short and it is possible to operate systems to supply a power load corresponding to a demand. We adopt a PI controller as a controller. The system is composed of double control loop in inner loop and in outer loop. In inner loop electric power is controlled and in outer loop electric energy is controlled. The controller parameters are designed using the pole-placement technique. The effectiveness of the proposed control system is confirmed by simulations. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(2): 58–66, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10200 [ABSTRACT FROM AUTHOR]

Generally a model of Metal Oxide Surge Arrester (MOSA) for numerical analysis uses a nonlinear resistance. But actual Voltage-Current (V-I) characteristics of MOSA have a hysteresis loop in the time domain like the i-Φ characteristic of a transformer and frequency dependency. The authors have investigated the relation between the actual V-I hysteresis characteristics obtained by some current waveforms and the static V-I characteristics. From the voltage difference between the above two characteristics, an equation was derived and a new model of MOSA was developed. This model consists of a nonlinear resistance representing the fundamental V-I characteristic, a linear inductance, and a voltage source that depends on the absorbed energy. The calculated results by the proposed model are compared with measurement results by using the waveform of standard impulse current, steep front current, and oscillated current. The accuracy of the model has been confirmed to be satisfactory. The model is expected to be useful to investigate insulation coordination of power systems. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 121(1): 35–42, 1997 [ABSTRACT FROM AUTHOR]

To analyze multifaults on a power line, many complex calculations must be performed. Hence, in many cases, computers are employed in the actual phase domain. However, it is difficult to determine the property and/or the physical meaning of the calculated results because the computer method is based on many complex numerical calculations. This paper represents a new analytical method for short-circuit studies which can deal with cross-country multifaults in a double-circuit transmission line with zero-sequence mutual coupling. This method is based on the well-known "two-component network theory" for a balanced three-phase double-circuit. Procedure steps are: (1) represent the network as seen from the faulted points with symmetrical component impedance; (2) construct the symmetrical equivalent circuits for faults with imaginary phase-shifting transformers; (3) combine these equivalents with each other and erase the symmetrical voltages at faulted points because the phase voltages at such points are known; and (4) calculate the currents at the faulted points by solving the simultaneous linear equations. This method is applied to an investigation of distance-relay "underreach" phenomena where cross-country multifault occurred on a double-circuit transmission line. Effects of line constants on these phenomena have been well understood. [ABSTRACT FROM AUTHOR]