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Electric power generated by photovoltaic (PV) systems is generally unstable because of uncertain meteorological conditions. Stably maintaining the supply‐demand balance of power systems requires an accurate prediction of the performance of PV systems. Especially for predicting the performance of the PV systems containing modules with different electrical characteristics or installed in different angles, it is necessary to calculate the generated power of the system by combining the current‐voltage (I‐V) characteristics of each module in series and parallel. Therefore, an accurate method is required for estimating the I‐V characteristics in various meteorological conditions. In this paper, a simple modeling method of the I‐V characteristics for crystalline silicon PV modules is proposed. The I‐V characteristics can be simulated in a good accuracy for practical use based on a simplified equivalent circuit of PV modules and a temperature correction of the short‐circuit current, open‐circuit voltage, and the current and voltage at maximum power point. The validity of the proposed method is examined by comparing simulated and measured I‐V characteristics of a PV module. Furthermore, to demonstrate the effectiveness of the proposed modelling method, it was applied to simulating the power generation of a PV system containing modules installed in different angles. [ABSTRACT FROM AUTHOR]

This paper proposes an optimal coil layout of wireless power transfer (WPT) systems for underwater vehicles (UVs). The power supply station adopts a multicoil arrangement with a double layer, and the UV also uses two receiving coils. The proposed WPT system for UVs has a reasonable advantage, where it does not request to adjust the relative position of coils. This paper experimentally discusses an optimal coil layout based on measurement results of a coupling coefficient. As a result, the proposed coil arrangement with the geometry rule realizes a certain power transfer under any positions and directions of UVs. [ABSTRACT FROM AUTHOR]

In the future, renewable energy (RE) generation systems will be constructed and interconnected to the power system by nonutility entities such as generation companies and residential customers. Therefore, generation expansion planning (GEP) should consider the effects of RE generation. The purpose of this paper is to discuss the best GEP from the economic, supply reliability, and environmental aspects considering the penetration of RE generation. For this purpose, this paper proposes a model of a utility's GEP process considering RE generation. The proposed method is based on stochastic dynamic programming (SDP) in which long-term uncertainties are modeled by geometric Brownian motion (GBM) and the binomial lattice process. The variation of RE generation output due to the weather conditions (short-term uncertainty) is also considered in the proposed method by means of the net load curve. [ABSTRACT FROM AUTHOR]

The quality of electric power caused by frequency fluctuation and voltage rise will be degraded because of the lightning surge and the mass introduction of distributed power. Thus, it is necessary to improve the performance of gas circuit breaker in order to maintain the stable supply of electric power. It has been reported that the arc conductance is calculated as the index of the current interruption in numerical analysis. However, few report have the measured value in the current interruption. This is because that the current interruption is the steep phenomenon of micro seconds range. Thus, it is necessary to establish the time‐high precision and noncontact measurement method. In this paper, the arc temperature is measured near current zero using the microsecond spectroscopic measurement. As a result, the microsecond spectroscopic measurement which combines the conventional spectroscope and the high speed video camera is 200 times faster than the measurement of conventional spectroscope. For this reason, the microsecond spectroscopic measurement is possible with the high speed video camera. Therefore, it is possible to measure the arc temperature with decreasing the current using the microsecond spectroscope. [ABSTRACT FROM AUTHOR]

SUMMARY This paper proposes a new estimation method to determine arbitrary circuit parameters for the harmonic analysis of a distribution network. Harmonic analysis is important in maintaining electric power quality. An interesting phenomenon, a temporary cut-down of the harmonic voltage level at dawn, even if demand is slightly increasing at this time, is often observed in actual power systems. This paper proposes to utilize observations of this phenomenon to estimate circuit parameters. In addition, it is claimed that a detailed equivalent circuit is preferable to a conventional simplified equivalent circuit for explaining the phenomenon. This paper also discusses the usefulness of the Harmonic Characteristics Curve, which is proposed in this paper as a new concept, at the secondary winding of the distribution transformer, and the correlation of PQ, the monitored values of the active and reactive power at the secondary winding of distribution transformer. This correlation should determine the equivalent fundamental frequency admittance of the shunt capacitors installed for distribution lines. © 2014 Wiley Periodicals, Inc. Electr Eng Jpn, 187(1): 16-23, 2014; Published online in Wiley Online Library (). DOI 10.1002/eej.22451 [ABSTRACT FROM AUTHOR]

In this paper, a new model of electric power supply‐demand analysis based on a clustered unit commitment (CUC) model is proposed. This method enables to derive daily generation plans in multi‐area by minimizing daily generation cost. In the CUC model, the generation units are clustered for the purpose of saving calculation time of the optimization. The proposed model is formulated by Mixed Integer Linear Programming (MILP). The numerical experiment of annual supply‐demand analysis was done to evaluate the availability of the proposed model. As a result, the availability of proposed model was clarified in the view of calculation time and operational results, which are derived by the numerical experiment. [ABSTRACT FROM AUTHOR]

Because of the significant changes in environmental policies and electric power deregulation in the last decade, a lot of photovoltaic generations (PV) have been and will be installed into the power system in Japan and the ratio of PVs to other synchronous generators will be increased. As a countermeasure against the decrease in the rotational inertia in the whole power system, a virtual synchronous generator (VSG) model control of the PV has so far been proposed. However, the system stabilization effect of the VSG in large‐scale power systems has been unclear. In this paper, a virtual step‐out blocking method of VSG for improving the transient stability is proposed. In addition, the necessity of governor control of VSG in a large‐scale power system is discussed. Finally, the rated kw and kwh capacities of the battery required for realizing the VSG‐model control are evaluated. [ABSTRACT FROM AUTHOR]

A photovoltaic (PV) array shows relatively low output power density, and has a greatly drooping current–voltage (I–V) characteristic. Therefore, Maximum Power Point Tracking (MPPT) control is used to maximize the output power of the PV array. Many papers have been reported in relation to MPPT. However, the current–power (I–P) curve sometimes shows multi-local maximum power points mode under nonuniform insolation conditions. The operating point of the PV system tends to converge to a local maximum output power point which is not the real maximal output point on the I–P curve. Some papers have tried to avoid this difficulty. However, most of those control systems become rather complicated. The two-stage MPPT control method is proposed in this paper to realize a relatively simple control system which can track the real maximum power point even under nonuniform insolation conditions. The feasibility of this control concept is confirmed for steady insolation as well as for rapidly changing insolation by simulation study using software PSIM and LabVIEW. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(4): 39–49, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20188 [ABSTRACT FROM AUTHOR]

SUMMARY This paper discusses power flow analysis and DC capacitor voltage regulation of a modular multilevel cascaded converter (MMCC) based on double-star chopper cells (DSCC). This analysis reveals the relationship between the circulating current through the DC link and the average power flowing out of or into each chopper cell. The DC component of the circulating current supplies half the active output power to the upper and lower strings of the chopper cells, while in contrast the fundamental frequency component transfers an amount of power between the upper and lower strings. Thus, the MDCC-DSCC can balance the capacitor voltages among the cells by controlling the amplitude of the fundamental frequency component of the circulating current. A new control method based on power flow analysis is employed, and its effectiveness is verified by circuit simulation. [ABSTRACT FROM AUTHOR]

With increasing demands for electric power, the electric power system is becoming more and more complicated, and the stable, highly reliable delivery of electric power is encountering two major problems, namely, large fault currents and power system instability. In particular, the fault currents occurring in power systems are tending to increase. To solve this problem, superconducting fault current limiters (SCFCLs) have been developed, and it is hoped that they will also solve the problem of power system stability. This paper describes the results of experiments on the improvement of power system stability and the suppression of fault currents with SCFCLs, performed with power transmission simulators. An experiment using an R-type SCFCL in a power system was performed. An R-type SCFCL was simulated by using a resistor and an electromagnetic contactor with thyristors. It was found that the inclusion of an SCFCL in the electric power system gives improved suppression of fault currents and improved power system transient stability. © 2000 Scripta Technica, Electr Eng Jpn, 133(4): 41–52, 2000 [ABSTRACT FROM AUTHOR]

SUMMARY This paper provides a fundamental analysis of a power supply and rectifiers for wireless power transfer using magnetic resonant coupling (MRC). MRC enables efficient wireless power transfer over middle-range transfer distances. MRC for wireless power transfer should operate at a high frequency in the industry science medical band, such as 13.56 MHz, because the size of the transfer device decreases at higher transfer frequencies. Therefore, the output frequency of the power supply on the transmitting side should be 13.56 MHz. In addition, the rectifier on the receiving side is operated at a high frequency. This paper focuses on the reflected power in the power supply and rectifiers. Thus, the parametric design method is clarified for the power supply, including a low-pass filter to match the output, the impedance of the power supply with the characteristic impedance of the transmission line. In addition, the effects on the rectifiers of silicon carbide and gallium nitride diodes are confirmed by performing an experiment and a loss analysis. [ABSTRACT FROM AUTHOR]

SUMMARY Because of significant change in environmental policies and electric power deregulation in the last decades, a lot of photovoltaic (PV) generations have so far been installed to the power system in Japan. When a huge amount of PVs generation is installed into the power system, we are very much concerned that the disconnection of the PVs due to a system fault has a big impact on the power system stability and transient voltage stability. So it is important to equip the PV with Fault Ride Through (FRT) function in order to maintain power supply-demand balance. In addition, Dynamic Voltage Support (DVS) function of the PV is effective to recover the voltage after the system fault. However, it is unclear how the PVs which are equipped with the FRT and DVS functions affect transient stability and voltage stability. In this paper, how the power factor of the PV power output affects the power system after a system fault is analyzed using P- δ curve. Then, a new PV power factor control method for improving the transient stability is proposed and its effectiveness is shown by digital simulations on a simple power system model. [ABSTRACT FROM AUTHOR]

The stabilizing facilities of power systems, i.e., series capacitor, system damping resistor, superconducting magnetic energy storage (SMES), phase shifter, etc., are used to improve the stability of synchronous generators. The control principle of these facilities to enhance the system damping is the same in the sense that these stabilizers control the active power so as to realize power systems. The generalized control method for these facilities has not been studied from the viewpoint of active power control. The generalized control method applying the variable structure control from the viewpoint of acceleration power for the synchronous generators is proposed in this paper. The variable structure control can be applied to both nonlinear and linear systems and has robustness against parameter variations. In this paper, the control law is derived first in general form from the viewpont of active power in the synchronous generator. This control law can take into account the automatic voltage regulator and governor effect indirectly. The feedback gains of the controller can be determined taking into account parameter variations in the synchronous generator. Second, this method is applied to the one-machine infinite-bus system with a variable series inductance so as to investigate the validity of this control method. The simulation results show that the controller is able to improve the system damping of the power system and is especially effective against parameter variation. [ABSTRACT FROM AUTHOR]

This paper presents first the harmonic output voltage-current characteristics of the synchronous generator. Next, the harmonic impedance characteristics of the power system are discussed taking into account the are filter. The harmonic impedance of the synchronous machine discussed in [2] is modified to derive more exact formula together with approximate expressions. The effect of the ac filter is not discussed in [2] but this paper shows that the overall harmonic impedance of the ac system is greatly dependent on the harmonic frequency characteristics of the ac filter. [ABSTRACT FROM AUTHOR]

SUMMARY In this paper, we propose three applications to quantitatively evaluate N-1 security with increased uncertainties. By using a robust dynamic security region (RDS), which is based on the concept of robust power system security (RS), the key region for judging the security and a new evaluation index for quantitative analysis, we can evaluate power system security as follows. (1) The calculation of the RDS at the time of yearly peak load demand can be recognized as the benchmark for the N-1 security at present, and this method can be applied to the future power system with increased renewable energy resources (RES) such as PV. (2) We show the yearly declining trend for N-1 security resulting from increased PV deployment year by year. (3) We calculate the necessary amount of additional power supply capacity, including conventional electric power generators or storage batteries, needed for maintaining the N-1 security at the present level. The effectiveness of the proposed method is demonstrated through simulations using a model system with three machines. [ABSTRACT FROM AUTHOR]

The power conversion efficiency of soft-switching inverters can be improved by using loss-less snubber commutation; however, the main switches of the inverter fail in zero-voltage turn-on when the output current is small. As a solution to this problem, adjustable dead time control in a loss-less snubber commutation according to the magnitude of output current has been proposed. Adjustable dead time control achieves zero-voltage turn-on of the inverter main switches in a loss-less snubber commutation in the range of low output current; however, waveforms of the output current of the inverter become distorted. In this paper, we propose a scheme for adjustable dead time control with dead time compensation for soft-switching inverters. The effectiveness of the proposed control scheme is verified by experiments. Experimental results demonstrate that when the proposed control scheme is adopted, the power conversion efficiency in the range of low output power improves up to about 3% and the THD is improved within 3%. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 180(1): 57-64, 2012; Published online in Wiley Online Library (). DOI 10.1002/eej.21282 [ABSTRACT FROM AUTHOR]

In recent years, there have been growing needs for accurate estimation of photovoltaic (PV) power due to the widespread use of PV power generation. PV power is usually estimated based on the amount of solar radiation, air temperature, and wind velocity. However, when the PV panel is covered with snow, the solar radiation is blocked by the snow and expected PV output cannot be obtained. In this paper, for accurate PV power estimation, we propose an Extended Lambert‐Beer law, and investigate a method to estimate the degree of attenuation of PV power by snow cover. And, accuracy verification of the proposed method is carried out with actual PV power records from when snow accumulated in the Tokyo Electric Power Company (TEPCO) service area in 2018. [ABSTRACT FROM AUTHOR]

Noncontact energy transfer systems are used in various fields in the industry. A high-frequency constant current must be supplied to the feeder of noncontact energy transfer systems. This paper proposes a high-frequency constant power supply for a noncontact energy transfer system using an immittance converter. When there are two or more pick-up coils on the feeder, the output of one pick-up coil does not affect other pick-up coils on the feeder if the feeder current is constant. We proposed use of an immittance converter to transform the high-frequency constant-voltage source into a high-frequency constant-current source. “Immittance converter” is a combined form of “impedance-admittance converter.” The immittance converter has input impedance that is proportional to the admittance of the load connected across output terminals. In this converter, the output current is proportional to the input voltage and the input current is proportional to the output voltage. Consequently, it converts a constant-voltage source into a constant-current source and a constant-current source into a constant-voltage source. This paper contains descriptions of the configuration of the new high-frequency constant-current power supply for noncontact energy transfer system, output characteristics versus excessive reactance and small frequency deviations for different values of the duty factor. The experimental results are also described. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(3): 81–89, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20438 [ABSTRACT FROM AUTHOR]

Application of a dispersed power supply system consisting of a large-scale photovoltaic system (PV), a fuel cell (FC), and an electric double layer capacitor (EDLC) is studied in this paper. This system is operated in autonomous mode, taking account of time delay characteristics of FC. The modified Euler type Moving Average Prediction (EMAP) model is improved using short-time fast Fourier transform (ST-FFT). The Adaptive Control type EMAP (AC-EMAP) model is introduced to reduce the capacity of EDLC. This system can meet the multi-quality electric power requirements of customers, and improve voltage stability and uninterruptible power supply (UPS) function as well. Moreover, the required capacity of EDLC to compensate the fluctuation of both PV output and Load demand is clarified by a simulation based on collaborative operation method by a prediction model using software MATLAB/Simulink. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(1): 13–24, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20262 [ABSTRACT FROM AUTHOR]

A severe fault may cause loss of synchronism of a small number of generators. And it may take many generators out of service resulting in a wide area blackout. When two groups of generators lose synchronism, the magnitude of voltage on some lines becomes zero. Therefore, an approach whereby lines with zero voltage are opened has been employed in order to prevent loss of synchronism from extension. This paper presents a new method using voltage and current measured on a line during disturbance to detect the line with zero voltage at the instant when loss of synchronism takes place. A method to detect loss of synchronism using voltage and current measured on a line was already proposed. This paper presents results of the tests performed using a power system simulator which is composed of a DC motor, a synchronous generator, artificial transmission line, circuit breaker equipment, and so on. The validity of the proposed methods was verified by finding loss of synchronism correctly. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(4): 7–19, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20346 [ABSTRACT FROM AUTHOR]

This paper discusses the synchronization phenomena of wind turbines in a wind farm. The phenomena illustrate the situation where a blade revolution of a wind turbine is pulled into phase with that of the other turbines in a wind farm. If blades of many turbines simultaneously pass in front of their towers, output power fluctuations of the turbines due to tower shadow effects also become synchronized. This causes voltage fluctuation to increase and may give rise to voltage flicker problems. The purpose of this paper is to examine the phenomena theoretically. Obtaining a differential equation that describes the phenomena with output power, voltage, and slip fluctuations of a wind turbine, we examine dependence of the phenomena on the related parameters. We also prove the validity of the equation through simulation analyses. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(1): 9–18, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20201 [ABSTRACT FROM AUTHOR]

Recently, the evaluation of control performances of interconnected power systems has become an important issue with respect to individual load frequency controls. Several performance measures are in practical use such as Area Control Error (ACE), Mutual Aid Criterion (MAC), and Control Performance Standard (CPS). Area Requirement (AR) is an alternative expression for ACE, where AR=-ACE. However, the characteristics of these indices have not been sufficiently studied as far as the authors know. In particular, this is the case for their dynamic behavior against random load disturbances. This paper investigates the performance index, AR, through analysis of two-area systems. Major dynamic elements of interconnected systems affecting the frequency are taken into account to investigate responses of the system against load disturbances. The analysis shows that, when new systems are interconnected, the smaller system tends to require more effort of control against load disturbances to keep the same value of the performance indices. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(1): 20–28, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20233 [ABSTRACT FROM AUTHOR]

A PV system's power output is not stable and fluctuates depending on weather conditions. Using a battery is one feasible measure to stabilize a PV system's power output, but it requires additional costs and results in additional waste of used batteries. In this paper, we propose a new measure for smoothing the short-term change in a PV system's power output, which is performed by tuning the characteristics of Maximum Power Point Tracking (MPPT) control without additional equipment. In our proposed measure, when the insolation increases rapidly, the operation point of MPPT control changes to a new point where the maximum power is not generated with the current insolation, so that the rate of increase in the PV system's power output is limited to a certain value. In order to evaluate the effect of the proposed measure on the operation of electric power systems, we evaluated the required capacity of generators for load-frequency control (LFC). It was revealed that the additional LFC capacity is not required even in the case where penetration of PV systems reaches 5% of the utility system's total capacity if the proposed measure is applied to all PV systems. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(2): 10–17, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20106 [ABSTRACT FROM AUTHOR]

This paper proposes a series active filter for mitigation of the third-harmonic voltage in a three-phase four-wire power distribution system in a building. The active filter which consists of a single-phase inverter can suppress the harmonic voltage of the system. The active filter is characterized by acting not only as a capacitor but also as a resistor for the third-harmonic components. A Hilbert transformer is applied to the controller of the active filter in order to realize accurate third-harmonic detection on a single-phase active filter. Measurement results of harmonic distortion of source voltage in a building is also shown in this paper. It is clarified in a simulation and experiment that the active filter can suppress the third-harmonic voltage without increasing neutral conductor current. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 62–70, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10379 [ABSTRACT FROM AUTHOR]

In this paper, the modified Euler type Moving Average Prediction (EMAP) model is proposed in order to operate a dispersed power supply system using new energy in autonomous mode. Furthermore, the EMAP model is used to operate a new type of dispersed power supply system consisting of a large-scale photovoltaic system (PV), a fuel cell (FC), and a small-scale superconducting magnetic energy storage system (SMES). This distributed power supply system can meet the multiple-quality electric power requirements of customers, and ensures voltage stability and UPS (Uninterruptible Power Supply) functions as well. Each subsystem of this distributed power supply contributes to the above-mentioned system performance with its own excellent characteristics. Moreover, the response characteristics of this system are confirmed by simulation with PSIM software, and, using collaborative operation under the EMAP model, the required capacity of SMES to compensate the fluctuation of both PV output and load demand is examined by simulation, using MATLAB/Simulink. [ABSTRACT FROM AUTHOR]

The immittance converter has an input impedance that is proportional to the admittance of a load connected across its output terminals. In this converter, the output current is proportional to the input voltage and the input current is proportional to the output voltage. Consequently, a constant-voltage source is converted into a constant-current source and a constant-current source into a constant-voltage source. The immittance converters consisting of only passive elements (inductors L and capacitors C) are suitable for use in the high-frequency links in power electronics applications. Previously, we proposed several types of immittance converters and some applications to power electronics equipment. In this paper, we propose a new three-phase immittance converter consisting of three L and C elements each to obtain an alternating current source from a three-phase voltage source without control. This paper presents a configuration of the new three-phase immittance converter that operates in either anti-phase or in-phase modes between the input voltage and the output voltage, and its voltage–current conversion characteristics and efficiency characteristics. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(1): 52– 58, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10169 [ABSTRACT FROM AUTHOR]

This paper deals with a self-commutated BTB (Back-To-Back) system for the purpose of power flow control and/or frequency change in transmission systems. Each BTB unit consists of two sets of 16 three-phase voltage-source converters, and their AC terminals are connected in series to each other via 16 three-phase transformers. Hence, the BTB unit uses totally 192 switching devices capable of achieving gate commutation. This results in a great reduction of voltage and current harmonics without performing PWM control. Simulation results verify the validity of the proposed system configuration and control scheme not only under a normal operating condition but also under a single line-to-ground fault condition. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(3): 68–78, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10124 [ABSTRACT FROM AUTHOR]

According to the deregulation of the electric power market and the improvement of small generators, the electricity supply by dispersed generators (DGs) is very attractive for both utilities and consumers. However, because of various types of DGs with low ratings, the introduction of a DG in a power distribution system increases the complexity of system operation. We propose on-line information exchange between DGs to facilitate autonomous operation of the distribution system. This paper evaluates the improvement of reliability of such a system by the on-line information exchange between DGs. The large-scale introduction of DGs might allow the power supply to the distribution system to be continued even if it is isolated from the upper system. We discuss the effects of information exchange on the system stability under islanding after an upper system failure. The analysis is performed in terms of instantaneous values calculated by using PSCAD/EMTDC. It is found that the transient stability improves when a DG with fast response speed and a DG with slow response speed exchange the information on inverse power flow to the network. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(3): 20–29, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10107 [ABSTRACT FROM AUTHOR]

This paper describes transient characteristics of a UPFC and its performance of suppressing power flow variation in a power transmission system having two parallel lines. The UPFC is installed in series with the two parallel lines and it controls the total power flow of the lines. Dynamic performance caused by a single line trip is theoretically and experimentally discussed. Experimental results reveal that a conventional control may produce an excessive power flow variation at the instant of the trip. On the other hand, the fast control scheme, which has been proposed by the authors, shows good performance of power flow control without any variation not only in steady state but also in transient state. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(1): 65–75, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.2011 [ABSTRACT FROM AUTHOR]

In recent years, the trend has been toward factors (e.g., demand for load, energy cost) becoming more and more uncertain in power system expansion planning. Thus, it has become necessary to take this uncertainty into account in determining generation plans. In this paper, a robust generation plan is defined explicitly as a plan that ensures fixed performance (economy) despite deviations in these factors. In addition, a new formulation of the robust generation mix problem, whose purpose is to determine the most robust combination of plants in a target year, is proposed. It is generally difficult to solve the formulated problem with parameters. However, by analyzing a proposed formulation from the viewpoint of optimization, we show that the proposed formulation is transformed into the conventional optimization problem without parameters. The simulation results on a typical model show that the generation mix produced by the proposed formulation is more robust than that produced by the conventional formulation. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(1): 26–35, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.2009 [ABSTRACT FROM AUTHOR]

The authors have proposed the Flexible Reliable and Intelligent Electric eNergy Delivery System (FRIENDS) as a future electric power distribution system. In order to realize FRIENDS it is indispensable to design the concrete interior structure of the key facility, the Quality Control Center. This paper proposes an interior structure and control schemes for the Quality Control Center from the viewpoint of customized power quality service, which is one of the most important objectives of FRIENDS. The validity of the proposed structure and control schemes is confirmed through transient analysis using PSCAD/EMTDC. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(3): 45–52, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.1159 [ABSTRACT FROM AUTHOR]

It is important to power system designers and operators to understand the conditions of a power system while it is in operation. As a means of understanding power system conditions, a new method using Superconducting Magnetic Energy Storage (SMES) has been proposed. This method is a new usage of SMES. Since SMES is a controllable power source with quick response, it can impart power disturbances with arbitrary patterns to power systems. The transient response resulting from the SMES power disturbance is analyzed by FFT. From the peak of the power spectrum, the natural frequency of the power system is determined. In the conventional method for diagnosis of the power system by SMES, the power disturbance is a continuous sinusoidal oscillation. In this paper, we propose to use the one-period sinusoidal wave as the power disturbance. This method is superior because the data for analysis come almost entirely from free oscillation and the periodicity of the disturbance does not appear in the analyzed power spectrum. In this paper, we show that the natural frequency of power systems can be measured by use of the proposed one-period sinusoidal SMES oscillation. © 2001 Scripta Technica, Electr Eng Jpn, 134(4): 43–49, 2001 [ABSTRACT FROM AUTHOR]

In planning a distribution system for an urban area, when a feeder is newly installed, the route of the feeder must be determined among many candidates, considering investment cost and constraints. However, it is difficult for planners to find the optimal route of the newly installed feeder, because too many candidate routes exist which can be constructed along roads in the service area of the power company, and it must be considered whether the end part of an existing feeder can be used as a part of a newly installed feeder within specified loaded value. In this paper, in order to support planners' decision making in selecting an optimal route for newly installed feeders, the authors have formulated the problem mathematically, and propose a new solution algorithm to find the optimal route by the Dijkstra method. Through numerical examples, the authors demonstrate the validity of the proposed method. © 1999 Scripta Technica, Electr Eng Jpn, 129(3): 40–50, 1999 [ABSTRACT FROM AUTHOR]

Today, a more effective power network is a key solution to the right-of-way problem in terms of transmission cost reduction. Various advanced techniques and planning methods are currently adopted in power utilities for this purpose. So far, the authors have presented two approaches for the rational coordination of transfer capability with transmission reliability. One is a method for numerical evaluation of the increase in critical transferable power resulting from lightning countermeasures on a long transmission route. The other is an index of the system margin to be uniformly allocated in a power system from the adequacy point of view. This paper proposes a new concept of system margin from the dynamic stability point of view and a new definition of probabilistic load transfer capability, both aiming for quantitative evaluation of power system alternative plans. Several different fault patterns have been taken into account, with their associated occurrence frequency and critical transferable power. These proposals are applicable to the practices of power utilities in conjunction with the conventional planning methods. This paper also illustrates numerical examples of the proposed methods as applied to a 500-kV trunk model power system. © 1999 Scripta Technica, Electr Eng Jpn, 128(1): 17–25, 1999 [ABSTRACT FROM AUTHOR]

This paper describes power swing damping control by HVDC power modulation. In a hybrid system (where the ac transmission system and the HVDC system compose a loop transmission system), damping control of power swing by control of HVDC power is called power modulation control. The new HVDC link between the Shikoku and Kansai power systems forms a loop transmission system consisting of the existing ac transmission system and the new HVDC transmission system; therefore, power modulation control can be applied for stabilization of the ac system. This paper deals with a newly developed power modulation control system to damp two power-swing modes occurring in a 60-Hz interconnected system and the neighboring power system to the HVDC converter station. Characteristics of power swings in an ac system, principles of power swing damping control by power modulation, the control system design method, and the results of verification tests by digital and analog simulators are described. It is shown that the developed power modulation system applied to the HVDC link is effective for damping two power swing modes. © 1998 Scripta Technica, Electr Eng Jpn, 124(3): 10–18, 1998 [ABSTRACT FROM AUTHOR]

A flywheel generator system composed of a doubly fed induction machine and an inverter feeding control current to the rotor coil of the machine has quick response in both effective and reactive power outputs. The application of such systems for the enhancement of power system transient stability has been widely investigated by simulations, where previously mostly phasor domain calculations have been performed. Targeting actual applications of the system, a more accurate and precise calculation method. i.e., in the time domain (instantaneous value-based), has been required. Recently the Electro-Magnetic Transient Program (EMTP) has been significantly improved and, without special difficulty, time domain calculation of transient stability involving doubly fed machines, inverter(s), synchronous machine(s), and detailed actual system parameters has become realistic. This paper describes EMTP calculations of transient stability enhancement phenomena by a doubly fed machine flywheel generator, together with items necessary for the application of EMTP to such calculations. Some results peculiar to time domain calculations are also presented. © 1998 Scripta Technica, Electr Eng Jpn, 124(3): 19–29, 1998 [ABSTRACT FROM AUTHOR]

This paper proposes a new electric power network that makes it possible for many types of dispersed generation plants owned by nonutility organizations to participate in an electric power market without the disadvantages of existing power utility and customers. This power network is called an open electric energy network (OEEN) because the network is open to the many types of plants for the participation. For achieving such openness, electric power storage devices, load controller at each customer and data communication network are installed in OEEN; the flow of excess electric power generated by each plant is controlled autonomously and in a distributed way. That is, the control is done by transmitting the data on excess electric power such as generation and demand point, power quality, price, etc., from each dispersed generation plant to the power storage devices and the load controllers through the communication network. Since this data-driven power flow control is similar to the mail system for a packet with the addresses of sender and receiver, it is called packet electric power transportation. In OEEN the storage device plays a different role from load leveling. Therefore, the way to determine the storage capacity differs from the conventional approach. In this paper, the applicability of queuing theory for determining the capacity is also discussed. [ABSTRACT FROM AUTHOR]

Harmonic interference problems generated by bulk semiconductor power converters become more serious in power systems with their wide use in industrial applications. Shunt passive filters consisting of LC tune filters or shunt active filters using PWM inverters have been used to suppress harmonic currents in distribution systems. To install the passive or active filters, it is necessary to find exactly a dominant harmonic source in distribution feeders. A harmonic power on each phase and order at a receiving terminal has been investigated by using a digital power meter including an FFT analyzer. However, the conventional detection method has a problem in that it is difficult to discuss exactly harmonic power flow because the detected harmonic power is much smaller compared with a fundamental active power at the receiving terminal. In this paper, the harmonic power in three phases, which can be detected on real time, is defined by applying the pq theory. Next, it is verified by a digital simulation that the proposed method can discuss harmonic flows more easily than the conventional method. As a result, it is more simple and precise to find the harmonic source. Moreover, measurement errors of the harmonic power are revealed quantitatively, and the validity of the proposed method is demonstrated by digital simulation. [ABSTRACT FROM AUTHOR]

Parametric oscillations which occur in a nonlinear two-phase uircuit with nonlinear reactors and capacitors are applied to many kinds of power devices. When the devices are operating under light load, the output voltage of these devices exhibits unstable oscillations, i.e., subharmonic oscillations, quasi-periodic oscillations or chaotic oscillations. This paper analyzes the abnormal oscillations and confirms the validity of the analysis experimentally. In this paper, new circuit equations are presented that can be applied to the analysis of a two-phase nonlinear circuit in which reactor saturation curves are sharp. It is clarified by this analysis that the parametric oscillations of the circuit which contains reactors of moderate saturation characteristics become subharmonic or quasi-periodic with the existence of resistances of the power supply side. Also, when the nonlinearity of the reactors in the circuit is sharp, the parametric oscillations may change into chaotic oscillations in addition to the aforementioned oscillations. [ABSTRACT FROM AUTHOR]

This paper presents a method for monitoring the dynamic stability of power systems using a Kohonen-type neural network. The QR factorization algorithm is widely used in eigenvalue calculations for power system dynamic stability studies, due to its numerical stability. However, the method has the drawback that the computational requirements increase as the cube of the problem size. The S-matrix method is therefore attractive, because it focuses on the most critical eigenvalue. However, this method is difficult to use in numerical calculations. The method proposed here makes use of a mapping of the eigenvalues that allows us to regard the absolute value of the most critical eigenvalue as a quantitative dynamic stability index. In this paper, a Kohonen-type neural network is used to estimate the index. The neural network is used to estimate the index. The neural network has the following advantages: (1) it uses a simple algorithm which requires no training signal, (2) it effectively classifies the input data, and (3) it presents at the outputs a two-dimensional mapping of the input data which makes it easy to visually comprehend their classification. [ABSTRACT FROM AUTHOR]

High performance power conversion requires high switching frequency power converters. Resonant dc link inverters, which are investigated in this paper, are suitable for this purpose because they cause no switching loss in principle. But in these inverters, loss of the resonant dc link inverters which can overcome these problems. First of all, we summarize the basic control principle of an ideal resonant dc link inverter. Then we present an analyzing method for the practical resonant dc link inverter introducing two equivalent circuits in which the influence of the power losses in the resonant link and in the inverter load is considered. From these equivalent circuits, the problems of existing control methods are clarified. Based on the results of this analysis, we proposed an optimum and keep the capacitor voltage at an allowable level. A simple compensation method for the influence of storage time of switching devices, which affects the implementation of the proposed control method, is described. [ABSTRACT FROM AUTHOR]

This paper describes the theoretical aspects of the flux-feedback type vector-control system based on the flux observer, emphasizing its robust stability to the rotor resistance variation. Section 2 clarifies a class of flux observers and derives the general structure and pole allocation which achieve the robustness to the rotor resistance variation. In section 3, it is pointed out that in the control system introduced in this paper, the possibility exists that the right half-plane will be zero in the open-loop transfer function from the exciter current iM to the estimated flux ¦λr¦ when the rotor resistance increases. We can avoid this by the pole allocation law of the flux observer. Furthermore, we establish the design criterion for the feedback gain and the pole allocation of the flux observer which guarantees robust stability of this control system by exploring the influence of such a zero on the flux feedback control system. Section 4 and 5 show that the proposed vector control system has an extremely low sensitivity to the rotor resistance variation in comparison with the slip-frequency controlled-type vector control system by theoretical and experimental approaches. [ABSTRACT FROM AUTHOR]

Companion paper [1] demonstrates that the installation of an ac filter may increase the low-order nontheoretical harmonic impedance resulting in the possibility of harmonic instability. This paper analyzes the harmonic impedance of ac/dc converter and its is used to calculate the harmonic voltage and harmonic voltage and harmonic current at the interconnecting point between ac and dc systems. The harmonic stability is also discussed using the calculated harmonic voltage and harmonic current. [ABSTRACT FROM AUTHOR]

West and many others have analyzed the subharmonic oscillation by equivalent transfer function method or describing function method. In these analyses, the nonlinear elements are represented by low-order polynomials or a simple piecewise-linear function. However, in practice, it is often necessary to represent the nonlinear characteristics by high-order polynomials. The conventional method to calculate the equivalent transfer function using a Fourier series requires a long computing time. The disadvantage becomes particularly remarkable in calculating the multiinput equivalent transfer function. To solve this difficulty, this paper proposes a method to calculate the equivalent transfer function numerically using a discrete Fourier transformation. The equivalent transfer function thus obtained is used for the analysis of 1/m-subharmonic oscillation. It is also applied to the analysis of the 1/3-subharmonic oscillation of a series-compensated power system. The analytical results are compared with the simulation results. This paper also proposes to set up a margin to the stable domain obtained by the equivalent transfer function in order to analyze the transient behavior of subharmonic oscillation. [ABSTRACT FROM AUTHOR]

There are two means of implementing eigenvalue control. One is to change the gains and time constants of controllers such as AVR, speed governors and SVCs. The other is to change the operating point of power system or equivalently the setting values of the controllers and consumption powers of load by changing over the secondary distribution system. The latter means is particularly effective for stabilizing a heavily loaded power system and it is discussed in detail in this paper. As experienced in the voltage stability phenomenon, midterm stability is greatly affected by the load characteristics such as dynamic behavior of induction motor and voltage dependence of static load. This paper discusses how to calculate the eigenvalue sensitivity with respect to the operating state of power system, taking into account the forementioned load characteristics. [ABSTRACT FROM AUTHOR]

The developments of SiC power devices has been proceeded remarkably since 1990. SiC power devices have been payed attentions as one of the candidate power devices for next HVDC transmissions and its R&Ds have been started in the KANSAI electric power company since 1995. In this paper, a series of R&Ds for the SiC devices and SiC inverters performed in the company are presented from the historical viewpoints. [ABSTRACT FROM AUTHOR]

SUMMARY Micro grids are expected to be one of the most realistic energy systems for efficient use of renewable energy sources with few adverse effects on the main electric power grids. However, it is difficult to maintain the supply-and-demand balance because distributed renewable energy generation units (DREGs), such as photovoltaic generation systems and wind turbine generation systems, generate a significant portion of electrical energy in the micro grids. Therefore, an operation planning method is needed considering the uncertainty in weather prediction in order to ensure stable micro grid operations. This paper presents an optimization method for operation plans of controllable generators in micro grids that copes with the uncertainty of DREG outputs. In the proposed method, the optimal operation plans are determined by, depending on the problem conditions, either an enumeration method or Tabu Search with preprocessing. Numerical simulations were carried out for a micro grid model in order to verify the usefulness of the proposed method. In the simulations, the daily operation plan and the modified half-hourly one were determined by the proposed method. As a result, we could obtain the optimal plans which had enough reserve margins for coping with the fluctuations caused by DREGs and demand. [ABSTRACT FROM AUTHOR]

SUMMARY For the effective and efficient insulation design of a power line, the return-stroke current waveform parameters are indispensable. Charge transfer is one of the important parameters when damage to equipment on a power line due to the energy of lightning is discussed. The amount of charge transfer associated with a lightning flash or individual strokes can be estimated by using the electric field change obtained with a slow antenna. The authors observed the electric field waveforms in south Kyushu for the purpose of efficient acquisition of return-stroke current parameters. In this paper, the authors discuss the relation between the negative first return-stroke current peaks and the impulse charge transfer based on the observed electric field waveforms. [ABSTRACT FROM AUTHOR]

SUMMARY: Spacecraft need high‐voltage power generation for high power. However, the high voltage can cause severe discharge problem on spacecraft. This paper describes the mechanism of spacecraft charging and discharging. Mitigation methods are also mentioned. [ABSTRACT FROM AUTHOR]

SUMMARY In order to implement the measurement and the evaluation of analog signals in high accuracy, to detect not only amplitude level but also phase information is necessary. For example, measurement of very small phase difference is desired in fields such as electric power and organism-related. Particularly, in organism-related field, impedance measurement is important and it is used to measure the urinary bladder volume, the respiratory volume, and so on. For these purposes, portable and real-time measurement devices with small sized is suitable. In this paper, we propose the urinary bladder volume measurement circuit using a simplified very small phase difference measurement circuit. This circuit is able to infer the changes of urinary bladder volume by measuring bioimpedance and phase difference of urinary bladder noninvasively with four-terminal method. [ABSTRACT FROM AUTHOR]