Since the present hierarchical grid structure and AC interface are so mature and too rigid, a new electric power system architecture is proposed here to save the Earth with renewable energy sources.The architecture consists of a new concept and a historical technology. That is network of many “electric power clusters” with DC interface. The cluster includes dispersed electric power generations, electric appliances, electric storage and “electric power router”. The router is equipment to resourcefully route electrical energy between such neighboring clusters and to manage electrical energy in the cluster. The transactions of electrical energy (inter clusters and/or intra cluster) and electric generations from renewal energy sources (like sun shine, wind, tide and bio gas) are intermittent and have very wide dynamic range, so, the interface must be by DC. When we achieve the energy society with the architecture, we will be able to reduce energy consumption, greenhouse gas and materials.

View full abstract

FRIENDS(Flexible, Reliable, and Intelligent Electrical eNergy Delivery System)is proposed as a new concept for a future power distribution system. One of the most important characteristics of FRIENDS is that QCC(Quality Control Center)as a new power quality control facility is installed very closely to customers. As one of the congurations of QCCs, AC-type QCC in which several Distributed Generators (DGs) can be installed easily has been proposed by authors. In FRIENDS concept, power exchange control between QCCs is included in fault case in upstream power system for higher reliability and making good use of power of distributed generators. A method to control several QCCs in fault case is proposed, and simulation results are shown in this paper.

View full abstract

Power system is a large dynamic system, which includes a lot of nonlinear elements. According to the nonlinear analyses using Hopf bifurcation theory, it can be detected that a limit cycle exists around an operating point, which may affect the global stability of power system significantly. The authors have proposed a numerical method to analyze the nonlinear characteristics in power systems by observing the power swing after some perturbation where the coefficients of nonlinear terms are determined by the least squares method. In this paper the method is modified for the application to a longitudinally interconnected power system including an excitation system to consider the inuence of the modal interaction on the nonlinear phenomena. In this method the system is approximated by a nonlinear coupled vibration model. Then the bifurcation characteristics are evaluated numerically based on the approximate model. The method has been applied to the low-frequency oscillation in IEEJ WEST10-machine system.

View full abstract

Transient stability assessment of the wind power generator is one of main issue in power system security and operation. The transient stability of the wind power generator is determine by its corresponding Critical Clearing Time(CCT). In this paper, we present the formulae to the transient behavior analysis and the transient stability analysis technique of induction generator used in wind power generating system at the three-phase fault condition. In the proposed method, the transient stability of the induction generator is analyzed using well known torque-slip and generator speed-time characteristics. The validity of the developed technique is confirmed with the results obtained from trials and error method using MATLAB/SIMULINK.

View full abstract

In recent years, there has been considerable interest in the on-line measurement, such as observation of power system dynamics and evaluation of machine parameters. On-line methods are particularly attractive since the machine’s service need not be interrupted and parameter estimation is performed by processing measurements obtained during the normal operation of the machine. Authors placed PMU (Phasor Measurement Unit) connected to 100V outlets in some Universities in the 60Hz power system and examine oscillation characteristics in power system. PMU is synchronized based on the global positioning system (GPS) and measured data are transmitted via Internet. This paper describes an application of PMU for generator oscillation analysis. The purpose of this paper is to show methods for processing phase difference and to estimate damping coeffcient and natural angular frequency from phase difference at steady state.

View full abstract

This paper proposes a new type of automatically tuned filter for HVDC Converter Station. The proposed method is largely based on the existing and reliable technologies, i.e. oil which is the most common insulation medium and the electromagnetic shield and coil configuration which is used for the air-core reactor.
The automatically tuning is achieved by changing the mutual inductance by opening and closing two or more cover coils (short-circuit coil) between the air-core coil and electromagnetic shield. The basic performance was confirmed through the shop tests of a prototype reactor and a small scale automatically tuned filter system.

View full abstract

Researches about the aerodynamics of wind turbine with straight wing vertical axis(SW-VAWT)are very limited, in spite of a number of advantages such as low dependence on wind direction variation and easy constructible straight blades. For these reasons, we are researching the lift type SW-VAWT for many years. The elucidation of the behavior of the flow inside and neighborhood of the wind turbine during the rotation is very important because of the performance improvement of the vertical axis wind turbine. This research examined to the aerofoil characters by using the numerical simulation technique and the precision of the prediction technique was confirmed as this result. Furthermore, we estimated flow behavior during the wind turbine rotation by using this numerical simulation technique, and evaluated the flow around the wind turbine. This paper presents outline and results of these calculations and evaluations.

View full abstract

This paper describes the effect of mutual leakage reactance in rotor circuit (Canay reactance) on analysis of generator transient and dynamic behavior. The authors derived a detailed equivalent circuit model for 48P-15.75MVA generator, and analyzed sudden short circuit and load rejection phenomena of the generator by simulations using the electromagnetic transients program (ATP-EMTP), and compared the results with the experimental data. In addition to these analyses, the influence of mutual leakage reactance on analysis of power system dynamic stability was investigated.

View full abstract

A large-scale installation of a photovoltaic power generation system (PV system) may cause some diculties in the operation of electric power systems. Taking into account a smoothing effect of power outputs of PV systems by dispersed installation, this paper discusses the LFC (Load Frequency Control) capacity for power output fluctuation of PV systems based on the insolation data simultaneously observed at 5 points around Nagoya, Japan. The main results are (1) the frequency deviation might not exceed the tolerance (0.05Hz)when the installed PV system is 2% of system capacity, which is Japan’s target value toward 2010, (2) when the larger capacity of PV system is installed, the frequency deviation would be larger than 0.05Hz, and the capacity of LFC generator must be increased, (3) the frequency deviation due to the installation of PV system might be larger in holiday with smaller electricity demand than in weekday.

View full abstract

This paper provides a case study of the performance and the economy of micro co-generation system (μCGS) for residential use based on a time series data on the hot-water demand obtained with 1 minute interval for one year. Assuming a simple constant output operation of PEFC, we calculated the composition of hot-water supply from PEFC and backup boiler. When μCGS is equipped with 100L hot-water storage tank, many portions of hot-water output of the PEFC were wasted although the backup boiler must assist to meet the demand concentrated within a short period. Annually, about 88% of the hot-water demand was met by the PEFC and the rest 12% was met by the backup boiler. Even in this case, the primary energy consumption was small as compared to the conventional energy system, because the electricity output from the PEFC could be fully utilized in the household or grid. However, because of a relatively higher price of city gas, the variable energy cost in μCGS was higher than that in the conventional system in the summer season. When the unit cost of PEFC is reduced to about 120, 000 yen/kW_e by a mass production, the annual cost on μCGS could be small relative to the conventional system.

View full abstract

In recent year, power generation from renewable energy sources is comming up. Particularly, wind power generation is attractive because of it’s advantages like, pollution free, no fuel cost, abundantly available in nature etc. However, the generated power is fluctuating and it mainly depends on the wind speed. These fluctuations will arise the bus voltage fluctuations and will cause power oscillations. A superconducting magnetic energy storage (SMES) unit based on a self-commutated inverter using Gate-turn-off (GTO) thyristor is capable of controlling both the active and reactive power simultaneously and quickly.
In this paper, control system conguration for active and ractive output power control of the series and parallel compensator which applied SMES is presented. Furthermore, this paper also describes the effectiveness of generating power leveling of transmission line and compensation of the generator’s terminal bus voltage instantaneous sag. It is show through simulations, that the controlling sequence of charging and discharging of the SMES coil effectively damps out the generator’s terminal bus voltage fluctuations and transmission line power oscillations.

View full abstract

Electric power generation using non-conventional sources is receiving considerable attention throughout the world. Wind energy is one of the available non-conventional energy sources. Electrical power generation using wind energy is possible in two ways, viz. constant speed operation and variable speed operation using power electronic converters. Variable speed power generation is attractive, because maximum electric power can be generated at all wind velocities. However, this system requires a rotor speed sensor, for vector control purpose, which increases the cost of the system. To alleviate the need of rotor speed sensor in vector control, we propose a new sensor-less control of PMSG (Permanent Magnet Synchronous Generator) based on the flux linkage. We can estimate the rotor position using the estimated flux linkage. We use a first-order lag compensator to obtain the flux linkage. Furthermore‚we estimate wind velocity and rotation speed using a observer. The effectiveness of the proposed method is demonstrated thorough simulation results.

View full abstract

The limited reserves of fossil fuels and environmental concerns have increased the interest in renewable energy. Actually, rapid advancement in the technology for utilization of renewable energy distributed generation is bringing opportunities of participating in power systems with financial assistance. However, there is much what remains only in performance evaluation of the renewable resource distributed generation, and it is often decient in consideration of the reliability of power systems. And verication about substitution of power transmission and distribution equipment capacity by distributed generation is inadequate. In particular, increase in equipment capacity of the low voltage class is not reflected in conventional evaluation. Recently, combined use of storage facility is practical because the economic conditions are improved and supply reliability will be secured.
In this report, we built a hierarchical structure model that considers explicitly several voltage classes of power systems in order to overcome these diculties, and analyzed potential of distributed renewable power generation and storage facility installation. As the result, the complementary role of electricity storage facility with intermittent renewable power generation was verified.

View full abstract

Due to the relatively high performance and the compactness, the pulsed-discharge deNO_x process is expected to be one of the next generation technologies to suppress air pollution. However, sufficient guide lines for the optimum operation of pulsed-discharge deNO_x process has not been presented. In this study, we have simulated numerically the process applied by several hundreds pulsed-voltages, and investigated the effects of by-products and ammonia injuction on the deNO_x performance. In a case for the no ammonia injection, both of the N_xO_y removal efficiency and the electric energy consumption to remove N_xO_y change with increasing repetitive pulse number, because electrons produced by the discharge recombine with accumulated by-products, such as of H₃O + (H₂O)₂, followed by decreasing radical concentration and oxidative/reductive removal reactions. In a case for ammonia injection, the removal efficiency increases and the electricity consumption decreases with increasing the ammonia concentration, because removal reactions such as NO →^O NO₂ →^OH HNO₃ →^NH₃ NH₄NO₃ and NO →^NH₂ N₂ become active. When ammonia is injected excessively, the deNO_x performance declines because the NH₂ radical produced by the electron collision with ammonia reacts with NO₂ to make relatively stable N₂O.

View full abstract

We have developed heat-resistant XLPE cable and accessories that can be operated at 105°C as the maximum permissible conductor temperature in normal operation. Through this cable system, greater transmission capacity can be achieved using existing cable ducts and without increasing the conductor size of the cable. We have developed heat-resistant XLPE insulation material which has a higher melting point than that of conventional XLPE. The breakdown strength of heat-resistant XLPE cable at 105°C is almost the same as that of conventional XLPE cable at 90°C. The heat deformation of the new cable at 105°C is almost the same as that of conventional XLPE cable at 90°C. Conventional self-pressurized rubber joints can be applied to heat-resistant cable lines with the new waterproof joint compound with low heat resistivity.

View full abstract

Capacity expansion problem is a hard combinatorial problem to solve because it must treat many scheduling subproblems within a multi-facility framework. It is classified into a category of general Investment & Operation planning problems. This paper presents a basic model for a certain class of capacity expansion problem applicable to the generation expansion problem in power systems, and proposes several mathematical methods for the model. In the field of Operational Research, Dynamic Programming (DP) has been the most popular method under multistage dynamic environments. It is however made clear in the paper that the model cannot be exactly solved by standard DPs. Consequently, another representative methods such as Lagrangian Relaxation, Branch-and-Bound and Heuristics are also tailored as alternatives for DP and compared with each other. Computational experiments by all proposed methods yielded promising suboptima with quality guarantee, among others Branch-and-Bound and Lagrangian Relaxation methods are recommended as suitable ones for the model.

View full abstract

This paper proposes the sensorless output power maximization control of the wind generation system. A permanent magnet synchronous generator (PMSG) is used as a variable speed generator in the proposed system. The generator torque is suitably controlled according to the generator speed and thus the power from a wind turbine settles down on the maximum power point by the proposed MPPT control method, where the information of wind velocity is not required. Moreover, the maximum available generated power is obtained by the optimum current vector control. The current vector of PMSG is optimally controlled according to the generator speed and the required torque in order to minimize the losses of PMSG considering the voltage and current constraints. The proposed wind power generation system can be achieved without mechanical sensors such as a wind velocity detector and a position sensor. Several experimental results show the effectiveness of the proposed control method.

View full abstract

For rationalizing equipment insulation level which can subsequently lead to reductions in the cost of substation equipment such as GIS’s and transformers, it is necessary to reexamine insulating test voltages by investigating the method of evaluating lightning surge waveforms in terms of the equivalent standard lightning impulse waveforms. This paper discusses the evaluation method of non-standard lightning impulse waveforms, based on the insulating characteristics of the insulating models of oil-lled transformers under such non-standard waveforms. The method is applied to a few typical cases and it turns out to be that the peak values are lowered by 10 to 30 percents in conversion to the standard lightning impulse waveform.

View full abstract

R-z two-dimensional numerical simulations have been carried out to investigate the performance of a largescale disk MHD generator coupled with radio-frequency (rf) electromagnetic field. The rf technique is verified to be useful even for a large scale MHD generator. The skin effect of plasma influences the distribution of rf electric field, however under the present plasma condition in the MHD generator, this effect will not induce the failure of rf application. When the plasma does not achieve the fully ionized seed condition only by self-induced Joule heating, the plasma is unstable. Coupling with the rf power can stabilize the plasma and improve the performance of generator. Thus, the present rf technique can help widening the actual operating condition of MHD generator.

View full abstract

XLPE which is the insulator of the XLPE cable will be oxidized by heat. But, an accident caused by oxidized XLPE has hardly reported until now. Therefore, oxidization of XLPE hasn’t been regard as important. But recently we found that XLPE cable used for a long time could break down due to the oxidization of XLPE by simulation result. So, we developed the service life estimation technique of oxidized XLPE cables used FT-IR.

View full abstract