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The experiments of pre‐ionized inert gas plasma MHD electrical power generation are conducted, and the performance and plasma behavior in the experimental generator are examined through time‐dependent r‐_ two‐dimensional numerical simulation. In the experiment, an enthalpy extraction ratio of 4.01% has been obtained with a disk‐shaped MHD generator with radio‐frequency pre‐ionization. In the numerical simulation, at an assumed inlet electron temperature around 5600 K (inlet ionization degree 0:10 × 10−4)_6600 K (1:36 × 10−4), the plasma structure is similar to the non‐uniform structure observed in the experiment. An enthalpy extraction ratio around 2_5% matches well with that in the experiment. At a suitable inlet electron temperature of 7000 K (3:15 × 10−4)_8000 K (1:79 × 10−3), although non‐uniform plasma structure still occurs, a high enthalpy extraction ratio over 10% is expected. [ABSTRACT FROM AUTHOR]

In recent years, the introduction of photovoltaic power generation systems has been increasing from the perspective of global warming countermeasures. However, there is a problem that it becomes difficult to adjust the supply and demand balance of electric power. Therefore, in this research, the inverter by using estimation signal estimates the load of the consumer, then we aim to adjust the supply‐demand balance at the demand side. By the verification of experimental, three‐phase inverter, which is assumed to be an industrial photovoltaic power generation system, estimates the load by using pseudo random binary sequence (PRBS) signal and two proposed methods. The load estimation results show that the error rate of the estimated resistance of each phase is within a few percent by using the two proposed methods, and the load estimation is achieved. [ABSTRACT FROM AUTHOR]

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]

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]

Recently, there has been a gradual increase in the use of battery powered electric multiple unit trains (EMUs), replacing the conventional diesel trains for nonelectrified lines of approximately 10-30 km. Battery powered EMUs are typically equipped with closed-type traction battery boxes, in which cooling fans are mounted. To improve the performance of battery cooling, we developed a control method for the cooling fans. Our novel method is derived from a thermal network model of the battery box, and is based on the temperature difference between the battery modules and outside air. We conducted an evaluation test for the Series BEC819, anAC-fed and battery-powered hybridEMUof JRKyushu. The test results demonstrated that the developed control method reduced maximum temperature of the battery by 1-2°C in comparison with the conventional constant speed control. [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]

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]

To improve noise and vibration of Electric Power Steering (EPS) system, we focus on the reduction of the sixth‐order radial force of an EPS motor by regulating its harmonic current. Because an EPS system is operated in a wide speed range, a reduction method is required to work even for dynamic motor speed. In this article, we introduce our method and report its test result to show the reduction of sixth‐order radial vibration of an EPS motor. [ABSTRACT FROM AUTHOR]

Presently, many wind turbine generators (WTGs) are connected to the power grid. While the penetration of wind power to the power system is increasing, FIT price is decreasing. Therefore, wind generation companies want to increase the electric power output from wind farms (WFs). In this article, we propose a control technique to reduce the influence of the wake by changing a power coefficient of each WTG in a WF for the purpose of improving electric power output of WFs. We showed the optimization technique of a power coefficient of each WTG and the effect of reducing the influence of the wake using measurement data from WFs. In addition, we formulated the wake effect as a function of distance between WTGs. We verified 1% improvement of generated energy in a year compared to the conventional control method by simulation. Furthermore, we quantified the improvement of generated energy output, using the distance between WTGs and the occurrence rate of the direction of the wind as a variable. [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]

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]

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]

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]

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]

SUMMARY In recent years, various storage battery systems, such as home battery system, V2H/V2G system, and UPS system, have spread rapidly all over the world. We propose a new power conversion system for use in the previously-stated storage battery systems. This paper describes operation analysis of this system for bi-directional power conversion with fundamental grid-interconnection. Good output follow-up controllability characteristics of the proposed system are shown through experimental results. [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]

SUMMARY Flexible photovoltaic (PV) modules have received a great deal of attention for use in PV systems. At present, the most important issue to be resolved is the optimum shape of flexible PV modules for obtaining maximum power output. A design tool specifically tailored for the flexible PV module is required for this purpose. In the present study, a new method is proposed for estimating the power output of a cylindrically shaped flexible PV module, taking into account the uneven irradiation and temperature that occurs for a curved surface. The average irradiation over the area of the entire module is used in the equation of the proposed method. The temperature is calculated based on the root mean square (RMS) of the irradiation over the area of the entire module. The average and RMS of the irradiation are calculated based on the directional dependence of the global horizontal irradiance. The estimated and measured power outputs are compared. The error rate of the total power output is 2.6%, and the mean absolute percentage error of the power output is 6.8%. The proposed method can reduce the amount of calculation to compare with a conventional method having the same mean absolute percentage error. [ABSTRACT FROM AUTHOR]

SUMMARY A contactless outlet for dc distribution systems is proposed. It uses an inductive contactless power transfer circuit with a series/parallel compensation circuit to prevent voltage fluctuation. However, the output voltage of the circuit rises in light load conditions. In this paper, the main circuit and control method for reducing the rise in output voltage and a method of estimating the output voltage are presented. The proposed circuit and methods were verified and evaluated experimentally using feedback control. [ABSTRACT FROM AUTHOR]

SUMMARY In recent years, a large amount of photovoltaic (PV) generation capacity has been installed in power systems. However, the power output from the PVs is random and intermittent in nature. Therefore, PV generation poses many challenges to power system operation. To estimate the impact of these issues on power system operation, we propose an optimal weekly demand and supply simulation method considering large penetration of PV generation. In this paper, an operation scheduling method considering optimal hot reserve capacity is studied. The effectiveness of the proposed method is shown by using Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

SUMMARY In this paper, we propose a multiagent-based electric power interchange method between microgrids (MGs). The proposed multiagent system consists of eight types of agent: a single micro virtual power plant (MVPP) agent , several MG controller agents (MGCs), several load agents, several gas turbine (gas engine) agents, several photovoltaic generation agents, several wind turbine generation agents, several battery agents, and a single grid agent. In the proposed system, the MVPP plays an important role, facilitating electric power exchange between MGCs. Simulation results suggest that the proposed multiagent system could improve the load factor and reduce the MG operation cost. [ABSTRACT FROM AUTHOR]

SUMMARY Electric vehicles (EVs) are expected to play a leading role in the changeover from fossil fuels to clean energy. However, EVs are currently not very popular, owing to their short cruising distance and long charging time. Wireless power transfer from the infrastructure to running EVs is expected to be the solution to these problems. Electric vehicle and electrified roadway (EVER) has been proposed as a wireless power transfer system for EVs while in motion. Via-wheel power transfer (V-WPT) is expected to be a wireless power transfer scheme for EVER. We designed and prototyped a 1:32 scale model of a V-WPT system that consists of an RF inverter, an electrified roadway, a rectifier, and an EV with a dc motor. The output power of the prototype RF inverter was 5.9 W and the dc-RF conversion efficiency was 36.6%. The LC matching circuits for the V-WPT were designed with two-port conjugate matching because S11 of the V-WPT was intrinsically -0.06 dB. After matching, the S11 value was reduced to -21.5 dB. The power transmission efficiency of the V-WPT system was 75%. The RF-dc conversion efficiency of the rectifier was 62%. The total efficiency of the EVER system was 24.2%. [ABSTRACT FROM AUTHOR]

SUMMARY Toward achieving a breakthrough in self-sustaining electric power generation systems consisting of a hydrogen energy cycle, we demonstrate an electrostatic induction potential superposed hydrogen electrolyzer to produce stoichiometric H [ABSTRACT FROM AUTHOR]

SUMMARY Since the output of photovoltaic (PV) generation includes power fluctuations caused by natural conditions, the installation of PV on a large scale is expected to affect load frequency control of the power grid. One method of compensating power fluctuations is the use of energy storage (ES), such as batteries and capacitors. A power fluctuation compensation system composed of an electrical double layer capacitor energy storage system (ESS) and a Li-ion battery energy storage system is considered. The power loss characteristics of both ESSs during power fluctuation compensation are modeled by equivalent circuits based on ES impedance spectra. The models are validated by experiments simulating power fluctuation compensation. Using these ES models, simulations were carried out to determine the power fluctuation dispatch method between the two ESSs and the capacity of the ESSs in consideration of power loss minimization. [ABSTRACT FROM AUTHOR]

SUMMARY It is desirable that the number of forward contracts traded on the Japan Electric Power Exchange increase. However, few studies have clarified what factors have contributed to impacting the number of forward contracts traded. In this study, the authors analyzed the number of forward contracts using four count regression models. The negative binomial regression model and the zero-inflated models were better able to express the expected counts, by incorporating the overdispersion and excess zeros present in the observed data. Among others, the spot market can carry positive influences on the expected counts, by about 12% for a 1 yen/kWh increase in price, and by about 27% for a 0.1%-point increase in volumes. The zero-inflated models revealed that as many as three-fourth of the entire forward products have a high probability of zero counts, while the remaining one-fourth may see an increased number of counts as the spot market price and/or the spot volume becomes higher. [ABSTRACT FROM AUTHOR]

SUMMARY Renewable forms of energy such as solar energy have attracted attention as alternative sources of fossil fuel. The output power of photovoltaic generation systems changes steeply. Changes in output power have an effect on the electric power quality of the power system. For that reason, a system which can smooth fluctuations of output power is required. In this paper, the moving average, modified moving average, single exponential smoothing, and double exponential smoothing methods are applied to electric power smoothing control schemes for distributed generation systems with photovoltaic generation. The reduction rate of power fluctuations and the maximum stored energy of electric double layer capacitors are adopted as system evaluation measures. To confirm the effectiveness of the power smoothing control methods, a distributed generation power system with photovoltaic generation systems is simulated with the power electronics circuit simulation software PSIM. The methods are then compared by evaluating the reduction in the capacity of electric double layer capacitors without loss in the power smoothing effect. [ABSTRACT FROM AUTHOR]

SUMMARY The high penetration of variable sources of renewable power generation will lead to operational difficulties in supply/demand balancing in the entire power system. The mass deployment of electric vehicles (EVs) and plug-in hybrid vehicles (PHEVs) will also cause significant changes in electricity demand. Therefore, controlling and managing the charging time of EVs/PHEVs are effective approaches that are imperative for improving balancing in power system operation. We assumed travel patterns for EVs in a model of the future Tokyo power system and analyzed the power system loads, including the charging load of the EVs, under several charging control scenarios. We verified that charging time controls are substantially effective for reducing the fuel costs in the power system. Further, we found that load leveling under a multicar charging management scenario gave the best results in terms of the fuel costs in all cases. [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]

SUMMARY This study experimentally clarified that changing the size of a charged object affects the characteristics of the electrostatic discharge (ESD) that occurs when a charged object moves toward a stationary, grounded object. The spark lengths and discharge currents were measured as charged, metallic, spherical electrodes of different diameters approached a stationary grounded object at different speeds. The charge voltages of the dc high-voltage power supply were +4.0 kV and +6.5 kV. According to the results, the average spark length tended to shorten with the speed of the spherical electrodes. The change in the average spark length with the speed of the 5.0-mm-diameter spherical electrode was faster than that for the 15.9-mm-diameter spherical electrode. The average peak value of the first peak of the discharge current for the 5.0-mm-diameter spherical electrode was greater than the average value for the 15.9-mm-diameter spherical electrode when the approach speed was greater than 5 mm/s for both spherical electrodes. The peak value, rise time, and rising speed of the first peak of the discharge current also correlate with the spark length, and the correlation can be explained qualitatively an the empirical equation deduced from the resistance formula proposed by Rompe and Weizel. [ABSTRACT FROM AUTHOR]

SUMMARY Electric railway vehicles require high electric power when powering and return high electric output when regenerating. Therefore, the fall in vehicle performance due to a voltage drop and the restriction on regenerative power due to a load shortage become problems in a dc-electrified railway. Therefore, energy storage devices (ESDs) are mounted on vehicles to assist the power of powering operation and to absorb the power of regeneration. In recent years, various hybrid vehicles have been studied because the performance of ESDs has become good enough for them to be mounted on vehicles. Generally, the design of the controller is a complicated problem because the vehicle operates under various running conditions. In this paper, a simple controller for ESDs is designed in the frequency domain. This controller aims at smoothing the input power and at managing the ESD energy. The proposed controller is examined under various running conditions with numerical simulations. [ABSTRACT FROM AUTHOR]

SUMMARY In the Tokaido Shinkansen, rolling stock types have been unified as an inverter controlled type, which was introduced after Series 300. As a result, the input power factor of the main converter used in the rolling stock has been controlled to 1. In accordance with this change, the role of reactive compensation of static var compensators (SVC) has shifted from the load power of trains to the power consumed by the reactance in the electrical power system. Therefore, when taking into consideration the aging of power converters, it is time to reassess their layout and the configuration for the future of the Tokaido Shinkansen. We reassessed the equipment configuration, capacity, and layout of power converters and verified the impact on the stabilization of the power supply when introducing self-commutated power converters. [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 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]

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]

This paper deals with estimation of total output of solar photovoltaic (PV) generators widely distributed in future power systems. In the proposed framework of estimation, the estimated signal in each frequency band is a linear combination of observed signals. The observation gain for each observed signal in each frequency band is designed through following two steps. First, an estimation error function is defined using assumed root mean square of output of PVs, predicted distribution of future PVs in the area, and correlation coefficients, which are identified in advance based on actual synchronized measurements of PVs. Second, observation gain in each frequency band is designed so as to minimize the estimation error function. The appropriateness of the proposed framework of estimation is demonstrated in small- and large-scale examples. [ABSTRACT FROM AUTHOR]

SUMMARY This paper presents the development of a new type of voltage regulator that can adequately maintain the voltage supplied to customers, dealing with the problem of voltage control that accompanies the widespread use of photovoltaic power generation systems. The newly developed device is a pole-mounted voltage regulator consisting of a step-down transformer that converts from high voltage to low voltage and a series transformer for voltage compensation. A demonstration test conducted at the CRIEPI Akagi Test Center confirmed that the voltage control function of the proposed voltage regulator is satisfactory, based on the proposed control algorithm. Simulation analysis, under the assumption of clustered installation of photovoltaic power generation systems, confirmed that the introduction of the proposed voltage regulator allows the system voltage to be adequately maintained and makes full photovoltaic power generation possible without suppressing the output. We anticipate that our proposed voltage regulator will be effective for adequately regulating the voltage in low-voltage distribution systems and will effectively promote even more widespread photovoltaic power generation. [ABSTRACT FROM AUTHOR]

SUMMARY Wireless power transmission via a sheet medium is a novel physical form of communication that utilizes a surface as a medium to provide both data and power transmission services. To efficiently transmit a relatively large amount of electric power (several watts), we have developed a wireless power transmission system via sheet medium that concentrates electric power on a specific spot by using phase control of multiple inputs. However, to find the optimal phases of the multiple inputs that let the microwave energy converge on a specific spot in the sheet medium, prior knowledge of the device's position and a preliminary experiment measuring the output power are needed. In the field of wireless communication, it is known that the retrodirective array scheme can efficiently transmit power in a self-phasing manner, which uses pilot signals sent by client devices. In this paper, we apply the retrodirective array scheme to our wireless power transmission system via a sheet medium, and propose a power transmission scheme using the phase-adjusted power transmission inputs. To confirm the effectiveness of the proposed scheme, we evaluate its performance by computer simulation and real-world measurement. Both results show that the proposed scheme can achieve retrodirectivity over wireless power transmission via a sheet medium. [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]

It is well known in the numerical simulations of a synchronous generator that the damper winding contributes to suppressing three-phase circuit unbalance in power systems. However, an experimental study has not been performed yet. In this paper, we verify experimentally the suppression of three-phase unbalance by the damper windings. In order to simulate the three-phase unbalance, a 470-W dispersed generator of single-phase two-line type was connected to a three-phase laboratory-scale power system that included a 6-kVA synchronous generator. We measured and analyzed line voltages and currents as well as damper bar currents both with and without the dispersed generator. The influence of damper windings on the unbalance of the three-phase circuit was also investigated. The results show that the damper winding contributes to improving the three-phase unbalance. [ABSTRACT FROM AUTHOR]

A new wind turbine generating system that employs a current-source thyristor inverter is proposed, and the steady-state and dynamic performances for a practical system are discussed. The proposed system is essentially based on the shaft generator system that is widely used in large ships, and it has many features such as high reliability and generation of output power of high quality. It is shown that electric power with constant frequency and voltage with low distortion can be obtained by using this novel system despite the changes in the velocity of natural wind. A dynamic model of the system is also developed, and a good agreement between simulated and experimental performances is obtained, thereby confirming the validity of the model. [ABSTRACT FROM AUTHOR]

In this paper, the authors propose a surge energy recycling converter. The proposed circuit is able to reduce the surge voltage of the secondary side and to recycle the surge energy in a DC-DC converter stage of a conventional front-end power supply. Thus, the use of low-blocking-voltage rectifier elements is possible, and the conduction loss is decreased. Further, the amount of surge energy that is wasted in a snubber circuit is decreased. As a result, the efficiency of the DC-DC converter stage is improved by about 1 percentage point. [ABSTRACT FROM AUTHOR]

This paper proposes a method for frequency control of a battery energy storage system applied for frequency deviation suppression in a power system including a large amount of wind power generation. A 5000- MW power system capacity with governor control and load frequency control is assumed for the study, and 500 MW of wind power generation capacity is assumed. The battery energy storage system is assumed to be added for frequency control in the power system. Suitable frequency control functions of the battery energy storage system and suitable capacity of the battery energy storage system which coordinate with conventional frequency controllers in the power system are reported. [ABSTRACT FROM AUTHOR]

It is generally believed that large battery systems will be needed to store surplus electric energy due to the high penetration of renewable energy (RE) such as photovoltaic generation (PV). Since the main objective of high penetra-tion of RE is to reduce C02 emissions, reducing kWh output of thermal generation that emits large amounts of C02 in power systems should be sufficiently considered. However, thermal generation plays an important role in load fre-quency control (LFC) of power systems. Therefore, if LFC could be performed with batteries and hydropower genera-tion, the kWh output of thermal generation could be re-duced significantly. This paper presents a method of LFC using batteries in a power system with highly penetrated PVs. An assessment of the effect of the proposed method considering mutual smoothing effect of highly penetrated PVs is made. [ABSTRACT FROM AUTHOR]

This paper presents an evaluation of the impact of extensive introduction of photovoltaic (PV) systems and stationary battery technology into the optimal power gen-eration mix in the Kanto and Kinki regions. The introduc-tion of solar PV systems is expected to be extensively deployed in the Japanese household sector and utility com-panies in order to address the concerns of energy security and climate change. Considering this expected large-scale deployment of PV systems in electric power systems, it is necessary to investigate the optimal power generation mix which is technologically capable of controlling and accom-modating the intermittent output-power fluctuations inher-ent in PV systems. Against this background, we develop both a solar photovoltaic power generation model and an optimal power generation mix model, including stationary battery technology, which can be used to explicitly analyze the impact of PV output fluctuations at a detailed time interval resolution such as 10 minutes for 365 consecutive days. Simulation results reveal that PV introduction does not necessarily increase battery technology due to the cost competitiveness of thermal power plants in the load-follow-ing requirement caused by PV systems. Additionally, on the basis of sensitivity analysis on PV system cost, dramatic cost reduction proves to be indispensable for PV to supply bulk electricity similarly to thermal and nuclear power plants. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(2): 9-19, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). [ABSTRACT FROM AUTHOR]

We developed a method for the design of distributed battery storage capacity for evaluating battery storage with demand-supply imbalance control in distribution systems to which large-scale home photovoltaic power generators are connected. The proposed method is based on a linear storage capacity minimization model with design-basis demand load and photovoltaic output time series subject to battery management constraints. We experimentally applied the design method to a sample distribution system with substation storage and terminal area storage. The developed method successfully reveals the charge-discharge schedule and stored power variation for design-basis demand load and photovoltaic output, satisfies the peak-cut requirement, and pinpoints the minimum distributed storage capacity. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(4): 29-37, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22324 [ABSTRACT FROM AUTHOR]

A large number of dispersed generators (DGs) are expected to be installed in distribution systems. Therefore, state estimation is an important problem for stable and reliable system operation. However, it is difficult to estimate the total power of DGs connected to a load-side system from a metering spot on the distribution line because at the metering spot only the sum of the active power from various loads and DGs can be measured. In this paper, we propose an estimation method for unknown DG outputs connected to a distribution system. This method enables to estimate DG outputs by analyzing power flow data measured at one spot, using independent component analysis (ICA). The estimation by ICA needs the same number of observations as estimations. However, the observation spots are extremely limited in existing distribution systems. Thus, we propose an estimation method which makes it possible to estimate DG outputs and load changes from single observations by using known information on the load power and a priori knowledge of insolation. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 180(1): 36-45, 2012; Published online in Wiley Online Library (). DOI 10.1002/eej.21275 [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]

The use of superconducting magnetic energy storage (SMES) for smoothing power fluctuations in a railway substation has been discussed. This paper proposes a smoothing control method based on fuzzy reasoning for reducing the SMES capacity at substations along high-speed railways. The proposed smoothing control method comprises three countermeasures for the reduction of the SMES capacity. The first countermeasure involves modification of rule 1 for smoothing out the average electric power to its average values. The other countermeasures involve the modification of the central value of the stored energy control in the SMES and revision of the membership function in rule 2 for the reduction of the SMES capacity. The SMES capacity in the proposed smoothing control method is reduced by 49.5% compared to that in the nonrevised control method. Computer simulations confirm that the proposed control method is suitable for smoothing out power fluctuations in substations along high-speed railways and for reducing the SMES capacity. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(2): 35-43, 2012; Published online in Wiley Online Library (). DOI 10.1002/eej.21175 [ABSTRACT FROM AUTHOR]

Renewable energy sources such as wind turbine generators and photovoltaics are intermittent in nature, thus resulting in fluctuating electric power. Leveling of their electric power is indispensable to realize large-scale renewable energy sources and to avoid severe power quality problems when they are interconnected into the grid. A battery energy storage system (BESS), combining batteries with a power converter and digital control, should be installed in the vicinity of an intermittent energy source. The fluctuating power is compensated by appropriately controlling active power stored in, or released from, the battery. This paper describes a 6.6-kV transformerless battery energy storage system based on a cascade multilevel PWM (pulse-width-modulation) converter, with focus on a control method for active power and SOC (state-of-charge) balancing. A down-scaled 200-V, 10-kW, 3.6-kWh (13-MJ) laboratory model using nine NiMH (Nickel Metal Hydride) battery packs was designed, constructed, and tested to verify the viability and effectiveness of the 6.6-kV system. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(1): 43-54, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21127 [ABSTRACT FROM AUTHOR]