Showing papers in "Electrical Engineering in Japan in 2007"
TL;DR: In this paper, the authors present the result of an experimental study of lightning overvoltages in wind turbine generation systems using a reduced-size wind turbine model, and the results show that the voltage rise due to tower footing resistance can cause a significant voltage difference between the tower foot and an incoming conductor led from a distant point.
Abstract: Wind turbine generation systems are built at locations where few tall structures are found nearby so as to obtain good wind conditions, and thus, they are often struck by lightning. To promote wind power generation, lightning-protection methodologies for such wind turbine generation systems have to be established. This paper presents the result of an experimental study of lightning overvoltages in wind turbine generation systems using a reduced-size wind turbine model. Overvoltages observed at wavefronts of lightning surges are focused on in this study. In the experiments, lightning strokes to one of the blades and to the nacelle were considered, and voltages and currents at various positions of the wind turbine model were measured. The following points have been deduced from the results: (i) The voltage rise due to the tower footing resistance can cause a significant voltage difference between the tower foot and an incoming conductor led from a distant point. Also, a voltage difference between the bottom of down conductors installed inside the tower and an incoming conductor can be of significance. (ii) The lightning current flowing through the tower body induces voltages in main and control circuits which form loops, and the induced voltages can cause overvoltages and malfunctions. (iii) Traveling-wave phenomena in a wind turbine generation system for a lightning strike to the tip of a blade and to the nacelle have been clarified from the measured waveforms. This information can be used for developing an EMTP simulation model of wind turbine generation systems. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 22– 30, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20466
42 citations
TL;DR: In this paper, the authors proposed a Magnetic Energy Recovery Switch (MERS), which consists of four MOSFET elements and one capacitor, and demonstrated the automatic correction of the power factor.
Abstract: In this paper, we propose a Magnetic Energy Recovery Switch (MERS). The switch consists of four MOSFET elements and one capacitor. A power factor improvement is automatically possible regardless of the impedance and power frequency of the load by synchronized switching of MERS with a power supply. MERS itself generates voltage and compensates for the inductance voltage unlike a conventional series capacitor, so that another DC power supply is not needed. An experiment was carried out to demonstrate the automatic correction of the power factor. We can also expect energy saving of electromachines such as an electric motor by the power factor correction with MERS. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(3): 56–62, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20321
25 citations
TL;DR: In this article, an ultra-high-speed permanent magnet synchronous motor drive is embedded in a turbocharger of an internal-combustion engine, which makes it possible to enhance output power of the turbochargers in a motoring mode and to retrieve combustion energy from exhaust gas in a regenerating mode.
Abstract: This paper describes an ultrahigh-speed permanent-magnet synchronous motor drive, which is embedded in a turbocharger of an internal-combustion engine. The electrical drive makes it possible to enhance output power of the turbocharger in a motoring mode and to retrieve combustion energy from exhaust gas in a regenerating mode. Computer simulations and experimental tests are conducted to examine various operation characteristics of a prototype. The experimental data demonstrate 220,000-r/min operation at 2.2-kW inverter output power, in good agreement with the simulation results and proving the feasibility of the proposed system. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(3): 31–40, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20408
24 citations
TL;DR: A new model-based expert system for fault section estimation using colored and timed Petri nets, which is suited for parallel processing so well that there is a possibility of reducing the inference time considerably.
Abstract: A correct and rapid inference is required for practical use of expert system for fault section estimation in power systems. This paper proposes a new model-based expert system for fault section estimation using colored and timed Petri nets. The Petri nets simplify the inference procedure greatly because it can represent the causalities among faults of power system components, protective actions of relays and circuit breakers. They can also represent the operating states of these protective devices explicitly, or, more precisely, whether a relay has been actuated correctly or falsely, etc. In addition, time sequence information on actuated relays and tripped circuit breakers can be handled by using the colored and timed Petri nets. Therefore, the operating states of relays and circuit breakers can be inferred more correctly.
Petri nets are suited for parallel processing so well that there is a possibility of reducing the inference time considerably. In the proposed system, the inference is executed by setting the initial states in the Petri nets using the information on the actuated relays and the tripped circuit breakers and then operating the Petri nets. There have been several test cases which used a prototype system on the Macintosh computer employing Object Common Lisp, and good results have been obtained.
23 citations
TL;DR: In this paper, the authors investigated the di/dt and dv/dt characteristics and the insulation recovery characteristic after interrupting the counterpulse current for various contact materials of AgWC, CuW, and CuCr.
Abstract: A high-speed vacuum circuit breaker (HSVCB) has been investigated. HSVCB makes high-frequency current superimposed on a fault current so that the current is forced to be zero and is interrupted. Its interruption performance is considered to be dependent on the rate of change of the current (di/dt). As a fundamental research, we investigated the di/dt– dv/dt characteristics and the insulation recovery characteristic after interrupting the counter-pulse current for various contact materials of AgWC, CuW, and CuCr. The results revealed that the case where the gap length is larger is better in a current interruption performance. Moreover, it was found that di/dt is not dependent on the insulation recovery characteristics, but the magnitude of interruption current is of great influence. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(1): 17– 25, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20362
22 citations
TL;DR: In this article, the electrical and magnetic characteristics of a PMIG under unbalanced grid voltages were analyzed using two-dimensional finite element analysis (2D-FEA) and the results were confirmed through experiments.
Abstract: This paper presents the electrical and magnetic characteristics of a permanent-magnet induction generator (PMIG) under unbalanced grid voltages. The method of symmetrical components and two-dimensional finite element analysis (2D-FEA) are used to calculate these characteristics and the results are confirmed through experiments. Even if the voltage of the power grids is unbalanced, the PMIG can operate at high efficiency over a wide range of slip and the built-in permanent-magnet (PM) rotor is minimally affected by the negative-sequence rotating field. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(4): 60–69, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20585
21 citations
TL;DR: It is found that the cell migration is enhanced by exposure to the magnetic field, depending on the kind of cell, and it is conjectured that the static magnetic field affects cell migration, which is downstream of the information transmission.
Abstract: The effect of a magnetic field on cells has long been investigated, but there are few quantitative investigations of the migration of cells. Cell migration is important as one of the fundamental activities of the cell. This study proposes a method to evaluate quantitatively the cell diffusion constant and the effect of a static magnetic field on cell migration. The cell lines are neuroblastoma (NG108-15), fibroblastoma (NIH/3T3), and osteoblastoma (MC3T3-E1). The static magnetic field of 30 or 120 mT is impressed by a permanent magnet in a vertical or horizontal direction to the dish. It is shown that the cell diffusion constant can represent the cell migration as the cell activity. It is found that the cell migration is enhanced by exposure to the magnetic field, depending on the kind of cell. It is conjectured that the static magnetic field affects cell migration, which is downstream of the information transmission. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(2): 46– 52, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20203
19 citations
TL;DR: In this article, the authors presented an output power leveling control strategy for a wind farm based on both the average wind farm output power and the standard deviation of the wind field output power.
Abstract: Effective utilization of renewable energies such as wind energy instead of fossil fuels is desirable Wind energy is not constant and windmill output is proportional to the cube of the wind speed, which causes the generated power of wind turbine generators (WTGs) to fluctuate In order to reduce the output power fluctuation of wind farms, this paper presents an output power leveling control strategy for a wind farm based on both the average wind farm output power and the standard deviation of the wind farm output power, a cooperative control strategy for WTGs, and pitch angle control using a generalized predictive controller (GPC) in all WTG operating regions Simulation results using an actual detailed model for wind farm systems show the effectiveness of the proposed method © 2007 Wiley Periodicals, Inc Electr Eng Jpn, 158(4): 31– 41, 2007; Published online in Wiley InterScience (wwwinterscience wileycom) DOI 101002/eej20448
15 citations
TL;DR: In this article, sensorless control for synchronous reluctance motors (SynRMs) without signal injection and an inductance measurement for position estimation are proposed, and the measurement method and the parameter adjustment method for improved stability of the closed loop are proposed.
Abstract: In this paper, sensorless control for synchronous reluctance motors (SynRMs) without signal injection and an inductance measurement for position estimation are proposed. In the case of SynRMs, accuracy of inductances is the most important factor in realizing precise position estimation because inductances are largely varied by a magnetic saturation phenomenon. Therefore, the inductance measurement method, which can measure appropriate inductances for position estimation, is important as well as a sensorless control method. The inductance measurement based on the observer is discussed, and the measurement method and the parameter adjustment method for improved stability of the closed loop are proposed. The proposed method can measure inductances easily and be applied for permanent magnet synchronous motors, too. Finally, the proposed sensorless control method is verified experimentally. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(4): 70– 80, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ eej.20274
12 citations
TL;DR: The grey system theory is a new tool which is very efficient for load forecasting which is applied to the long-term load forecasting from three aspects: the point prediction; the interval prediction; and the topological forecasting.
Abstract: Supply and demand in power system planning and operation is required to be balanced. An operational reserve for protection against faults or accidental demands also is required. Therefore load forecasting is one of the most important fields and various load forecasting methods have been applied.
In this paper the grey system theory which mats uncertain information is applied to the long-term load forecasting from three aspects: the point prediction; the interval prediction; and the topological forecasting. In the point prediction, the annual total demand is predicted, in the interval prediction, the annual peak demand is predicted, and in the topological forecasting, the date where a yearly maximum peak demand would occur is predicted. The grey dynamic model (abbreviated as GM model) is adopted as the predicted model. The GM model is a differential equation model which is different from most forecasting models. The GM model is quite powerful when combined with the preliminary transformation called the accumulated generating operation (AGO).
This paper proposes a new method for the long-term load-forecasting problems involving uncertainty. The predicted results have been found to be very satisfactory. The grey system theory is a new tool which is very efficient for load forecasting.
12 citations
TL;DR: In this paper, a swing-up and stabilizing control strategy for a cart-pivotal pendulum system is proposed, which makes it possible to determine an appropriate switching angle more arbitrarily.
Abstract: This paper addresses a swing-up and stabilizing problem for a cart– pendulum system, which consists of a pendulum and a motor-driven cart. Existing methods are based on the strategy of swing-up of the pendulum by energy control methods, then switching the controllers to balance the pendulum when it approaches the upright position. The switching angle influences significantly control performance, so the pendulum might fall down if the angle is inadequately chosen. This paper proposes a swing-up and stabilizing control method which makes it possible to determine an appropriate switching angle more arbitrarily. In addition to the energy control method for swing-up, a stabilizing method based on controlled Lagrangians is adopted instead of a linear controller. The attractive domain of the closed-loop system with this method can be known in advance and is wider than with linear controllers. In this way, our proposed control strategy overcomes the difficulty in choosing the switching angle of the controllers. An experimental result illustrates the effectiveness of the proposed method. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(4): 24– 31, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20534
TL;DR: In this paper, the authors evaluate the reduction of LSE's purchasing cost from the electricity market and other LSEs' purchasing cost by introducing Energy Storage System (ES) to customers.
Abstract: In Japan the electricity market will open on April 1, 2004. Electric utility, Power Producer and Supplier (PPS), and Load Service Entity (LSE) will join the electricity market. LSEs purchase electricity based on the Market Clearing Price (:MCP) from the electricity market. LSEs supply electricity to the customers that contracted with the LSEs on a certain electricity price, and one to the customers that introduced Energy Storage System (:ES) on a time-of-use pricing. It is difficult for LSEs to estimate whether they have any incentive to promote customers to introduce ES or not. This paper evaluates the reduction of LSEs' purchasing cost from the electricity market and other LSEs' purchasing cost by introducing ES to customers. It is clarified which kind of customers has the effect of decreasing LSEs' purchasing cost and how much MCP of the whole power system the demand-side energy storage systems change. Through numerical examples, this paper evaluates the possibility of giving the cost merit to both customers with energy storage systems and LSE by using real data for a year's worth of MCP. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(1): 22–35, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20447
TL;DR: In this article, the influence of physical parameters such as current density, channel radius, and pulse duration of one micro-discharge under a constant reduced electric field strength was investigated to improve the NO removal performance.
Abstract: To improve the NO removal performance in silent discharge process, we investigated the influence of physical parameters such as current density, channel radius, and pulse duration of one micro-discharge under a constant reduced electric field strength. The influence of micro-discharge occurrence locations was also discussed. In order to analyze the NO removal process, we assumed that the pulse micro-discharges occur repeatedly at the same location in static gas and that the chemical reactions induced by micro-discharge form many radicals, which react with pollutants and by-products. The conclusions we obtained are that lower current density, smaller discharge radius, and shorter discharge duration improve NO removal efficiency. These results also mean that the lower discharge energy of one micro-discharge and the larger number of parallel micro-discharges increase the NO removal performance. Therefore, making the area of one micro-discharge small is a desirable way to improve the NO removal performance. Thus, we think that the glow-like discharge might be more effective than the streamer-like discharge mode. Next, using the two-dimensional model, which considered the influence of gas flow, we found that the repeated micro-discharges at different positions are very effective to increase the De-NOx performance. The reason is that the reaction of NO2+ONO+O2 and ozone dissociation reactions are suppressed by the movement of the location of micro discharges. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(3): 1–9, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20556
TL;DR: In this paper, a new method for transient stability analysis in power systems is proposed, which directly computes the critical trajectory for a given contingency to obtain the critical condition of the studied system.
Abstract: This paper proposes a brand-new method for transient stability analysis in power systems. The proposed method directly computes the critical trajectory for a given contingency to obtain the critical condition of the studied system. Although the method may be useful for general nonlinear dynamic systems, it is applied to the problem of obtaining a controlling UEP, unstable equilibrium point, which provides inevitable information for the energy function methods to assess transient stability. Namely, the proposed method effectively yields a critical trajectory on PEBS together with the controlling UEP, thus improving the conventional BCU method. The effectiveness of the proposed method is demonstrated in 3-machine 9-bus and 6-machine 30-bus systems. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(3): 26–33, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20245
TL;DR: This paper describes an adaptive strategy for tuning the parameters of the PSO method based on some numerical analysis of the behavior of PSO, which utilizes the information about the frequency of an updated global best of a swarm.
Abstract: The Particle Swarm Optimization method is one of the most powerful optimization methods available for solving global optimization problems. However, knowledge of adaptive strategies for tuning the parameters of the method for application to large-scale nonlinear nonconvex optimization problems is as yet limited. This paper describes an adaptive strategy for tuning the parameters of the PSO method based on some numerical analysis of the behavior of PSO. The proposed adaptive tuning strategy is based on self-tuning of the parameters of PSO, which utilizes the information about the frequency of an updated global best of a swarm. The feasibility and advantages of the proposed adaptive PSO algorithm are demonstrated through some numerical simulations using three different typical global optimization test problems. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(4): 38– 46, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20487
TL;DR: In this article, two types of speed sensorless converters were proposed to control rotational speed and electric power in a wind turbine, one based on a slip frequency control system and the other based on vector control system.
Abstract: This paper proposed two types of speed sensorless converters that can control rotational speed and electric power. One is based on a slip frequency control system. The other is based on a vector control system. The rotational speed of the wind turbine is estimated with the phase voltage and phase current of the induction generator by the adaptive rotor flux observer. The estimated wind turbine rotational speed ωrest is used as the feedback of the speed control loop in the converter control system. Also, the estimated rotor flux ϕ2dest is used for the vector control. The simulation results confirm that both of them perform satisfactorily under the speed sensorless operation. The method based on the vector control system generates more electrical energy than does the method based on the slip frequency control system. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(4): 62–75, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20323
TL;DR: In this article, the shape and position of the triangle slot influenced the broadband characteristics of a bow-tie antenna with various slots, and it was shown from the simulation results that the shape of the slot influenced greatly the broadband properties of the antenna.
Abstract: For electromagnetic compatibility, broadband antennas are important for measurements of fast pulse transient electromagnetic phenomena and broadband characteristics due to noise and high-frequency interference. We analyzed the characteristics of a semicircle type bow-tie antenna with various slots using the FDTD method. It was shown from the simulation results that the shape and position of the slot influenced greatly the broadband characteristics of the antenna. We confirmed that a semicircle type bow-tie antenna with a triangle slot was effective for a broadband antenna. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(4): 47–53, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20252
TL;DR: In this article, the authors presented the corona characteristics, particularly the audible noise, of conductors having various wetting properties for the purpose of developing a corona-free conductor for AC overhead transmission lines and found that a conductor having a super-hydrophobic surface exhibited a minimized audible noise level, but it does not have sufficient durability for practical applications.
Abstract: Corona discharge may cause audible noise, and it is frequently generated from wet conductors of high-voltage AC overhead transmission lines. Audible noise arises more easily from new conductors that have lubricating oil on their surface than from aged conductors. In this paper, the corona characteristics, particularly the audible noise, of conductors having various wetting properties are presented for the purpose of developing a corona-free conductor for AC overhead transmission lines. It was found that a conductor having a super-hydrophobic surface exhibited a minimized audible noise level, but it does not have sufficient durability for practical applications. Furthermore, a conductor having a super-hydrophilic surface made by thermal spraying of TiO2 showed good performance regarding the suppression of audible noise. The thermal spraying of TiO2 seems to be an effective processing technique that has sufficient durability for practical applications. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(3): 19–25, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20509
TL;DR: In this article, a three-dimensional numerical analysis of a liquid metal MHD generator has been carried out, and the effect of the electrode width on the performance has also been examined, taking account of the current flow in the electrode.
Abstract: Three-dimensional numerical analysis of a liquid metal MHD generator has been carried out. The three-dimensional structures of the electromagnetic field and fluid flow in the MHD generator have been clarified, and the effect of the electrode width on the performance has also been examined, taking account of the current flow in the electrode. Structures of the electromagnetic field and fluid flow are complicated owing to the three-dimensional current flow, induced magnetic field, and Lorentz force. The highest performance is found to be obtained when the width of the electrode is equal to that of the generator. The performance predicted from three-dimensional analysis is somewhat lower than that from two-dimensional analysis because of the larger input power. The increase in the input power is attributed to the increase in Lorentz force caused by less reduced magnetic flux density and to the additional friction loss on the insulator walls (x−y plane). © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(3): 19–26, 2007; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/eej.20282
TL;DR: In this article, a sensorless control system of a permanent magnet synchronous motor (PMSM) is proposed, which does not need parametric information beforehand. But, the motor starts by the signal injection sensorless controller, and the sensorless scheme changes to an extended EMF estimation scheme.
Abstract: The model parameters of a permanent magnet synchronous motor (PMSM) are required for high-performance control and a model-based sensorless control. This paper proposes a sensorless control system of PMSM that does not need parametric information beforehand. The parameters of a PMSM drive system, including the inverter, are identified at standstill and under operating conditions. At first, the initial rotor position is estimated by a signal injection sensorless scheme in which the machine parameters are not required. After the initial position has been estimated, the resistance, including the on resistance of the IGBT, the voltage error caused by dead time in the inverter, and d-axis and q-axis inductances, are identified at standstill. After the motor starts by the signal injection sensorless control, the sensorless scheme changes to an extended EMF estimation scheme. The estimated parameters for the resistance, and daxis and q-axis inductances are used in such sensorless control. The magnet flux-linkage, which cannot be estimated at standstill, is identified under the sensorless operation at medium and high speeds. The effectiveness of the proposed method is verified by several experimental results. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(2): 68–76, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ eej.20548
TL;DR: In this paper, the authors quantify the relationship between significant arm-clutch loading, leg restriction, and motor paralysis, and analyze lumbar joint trajectories in the orthotic gait of paraplegic subjects and in the ordinary and orthotic gaits of a normal subject, by using an inverted pendulum model.
Abstract: In this study, we attempt to quantify the relationship between significant arm-clutch loading, leg restriction, and motor paralysis, and analyze lumbar joint trajectories in the orthotic gait of paraplegic subjects and in the ordinary and orthotic gaits of a normal subject, by using an inverted pendulum model. With leg restriction, the trajectories are located in front of an equilibrium point of the inverted pendulum, and the loading is higher due to the influence of the gravity moment. Comparing the trajectories of paraplegic and normal gait with orthosis in the horizontal plane, the trajectory in the paraplegic subjects was rectilinear, while that in the normal subject was curved in the direction toward the equilibrium point. The loading is lower in the curved trajectory than in the straight trajectory because of the trade-off between gravity and inertia. These results suggest that the increase in the distance between the trunk movement and the equilibrium point of the inverted pendulum results in significant loading due to leg restriction and motor paralysis in the orthotic gait of paraplegics. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(3): 10– 21, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20533
TL;DR: In this paper, a novel strategy of maximum-power-point tracking for photovoltaic power generation systems is described, which is the capacity to see the maximum power point using only a single transducer, that is, a Hall-effect CT or an isolation amplifier.
Abstract: This paper describes a novel strategy of maximum-power-point tracking for photovoltaic power generation systems. A unique feature of this method is the capacity to see the maximum power point using only a single transducer, that is, a Hall-effect CT or an isolation amplifier. Output power of the photovoltaic can be estimated with an average value and ripple amplitude of the detected reactor current or the capacitor voltage. A conventional hill-climbing method is employed to seek the maximum power point, using the output power estimated with only the current or voltage transducer. In this paper, not only a theoretical aspect of the proposed method is discussed, but also experimental results are presented to prove the feasibility of the method. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(1): 79– 86, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20275
TL;DR: Multidirectional Associative Memory (MAM) can deal with multiples of many patterns, such as (x1,x2,…), where xm is the pattern on layer m.
Abstract: Hopfield model is a representative associative memory. It was improved to Bidirectional Associative Memory (BAM) by Kosko and to Multidirectional Associative Memory (MAM) by Hagiwara. They have two layers or multilayers. Since they have symmetric connections between layers, they ensure convergence. MAM can deal with multiples of many patterns, such as (x1,x2,…), where xm is the pattern on layer m. Copyright © 2004 Wiley Periodicals, Inc.
Noest, Hirose, and Nemoto proposed complex-value Hopfield model. Lee proposed complex-valued Bidirectional Associative Memory. Zemel proved the rotation invariance of complex-valued Hopfield model. It means that the rotated pattern in also stored.
In this paper, the complex-valued Multidirectional Associative Memory is proposed. The rotation invariance is also proved. Moreover it is shown by computer simulation that the differences of angles of given patterns are automatically reduced.
At first we define complex-valued Multidirectional Associative Memory. Then we define the energy function of network. With the energy function, we prove that the network ensures convergence.
Next, we define the learning law and show the characteristic of recall process. The characteristic means that the differences of angles of given patterns are automatically reduced. Especially we prove the following theorem. In the case that only a multiple of patterns is stored, if patterns with different angles are given to each layer, the differences are automatically reduced.
Finally, we investigate whether the differences of angles influence the noise robustness. It is found to reduce the noise robustness, because the input to each layer becomes small. We show this by computer simulations. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(1): 39–45, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20387
TL;DR: In this paper, a position sensorless control of an interior permanent magnet synchronous motor (IPMSM) is presented. But, this method requires the rotor position information to control the motor torque, and this is generally detected by mechanical position sensors such as encoder or resolver.
Abstract: Driving a permanent magnet synchronous motor (PMSM) requires the rotor position information to control the motor torque, and this is generally detected by mechanical position sensors such as an encoder or a resolver. However, these sensors increase the machine size and the cost of the drive, and reduce reliability of the system. Therefore, many papers about position sensorless drive method of PMSM have been published. This paper presents a position sensorless control of interior permanent magnet synchronous motor (IPMSM). A mathematical model of IPMSM using the extended electromotive force (EMF) in the rotating reference frame is utilized to estimate the rotor speed and position. This model has a simple structure integrating position information into the extended EMF term. Therefore, the sensorless control based on the mathematical motor model can be implemented simply. The estimation method proposed is based on the principle that the error of the current is proportional to that of extended EMF. This method was carried out using a 6-pole, 400-W, 1750 r/min test motor system. It was found that sensorless speed control was achieved from 80 r/min to 1800 r/min under 0 to 100%loads. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(3): 41–48, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20406
TL;DR: In this article, a high efficiency and high power chopper based on a novel soft switching scheme QRAS (Quasi-resonant Regenerating Active Snubber) has been proposed.
Abstract: A high-efficiency and high-power chopper based on a novel soft switching scheme QRAS (Quasi-resonant Regenerating Active Snubber) has been proposed in this paper. Operating efficiency of the proposed QRAS has been investigated by simulation and experiments. For the purposes of this study we fabricated a one-tenth prototype model and tested it under the rated load, light load, current discontinuous mode, and under operation out of the resonant stable operational region. The overall evaluation of these test results is provided and the possibility of implementation of an 80-kW practical model is demonstrated by these successful test results. In addition, as an approach to the next study, the feasibility of 8-kW SiC-QRAS is examined and a preliminary evaluation of the efficiency enhancement due to the use of silicon carbide (SiC) power devices is given based on successful experimental results. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 68– 80, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20439
TL;DR: In this article, the authors proposed a new method of discriminating a magnetizing inrush current and a short-circuit fault current by using the discrete wavelet transform (DWT), which provides the function of detecting discontinuity of the current waveform.
Abstract: Customers who need electricity of higher quality have recently been installing cogeneration facilities. They can avoid voltage sags and other distribution system-related disturbances by supplying electricity to important loads from their generation equipment. As another example, the FRIENDS highly reliable distribution system using semiconductor switches or storage devices based on power electronics technology, has been proposed. These examples illustrate that the need for high reliability of power supply in distribution systems is increasing. Fast relaying algorithms are indispensable in order to realize these systems.
The author proposes a new method of discriminating a magnetizing inrush current and a short-circuit fault current by using the discrete wavelet transform (DWT). The DWT provides the function of detecting discontinuity of the current waveform. An inrush current occurs when a transformer core becomes saturated. The proposed method detects spikes of the DWT components derived from the discontinuity of the current waveform at both the beginning and end of the inrush current. Wavelet thresholding, a form of wavelet-based statistical modeling, was used to detect the spikes of DWT components. The proposed method was verified by experimental data obtained from field tests using a single-phase transformer and the proposed method was demonstrated to be effective. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(3): 19–28, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20461
TL;DR: In this paper, experimental and analytical studies on lightning surge characteristics of a ground mesh were carried out under various conditions, including earth resistances, current injection points, and injection current waveforms.
Abstract: Lightning surge characteristics of a ground mesh have an influence on electromagnetic transient behaviors in low-voltage and control circuits. This paper describes experimental and analytical studies on lightning surge characteristics of a ground mesh. The experimental studies are carried out under various conditions. The experimental parameters considered in this measurement include earth resistances, current injection points, and injection current waveforms. These measured results are compared with calculated results based on the theoretical studies by Sunde. A comparison of the measured results with the calculated results shows good agreement. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(4): 16– 23, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20559
TL;DR: In this paper, a quantitative analysis method for PV system output and losses was developed to clarify the behavior of grid-connected PV systems. But the output loss will be larger in the high-density case.
Abstract: The voltage of power distribution lines will be increased due to reverse power flow from grid-connected PV systems. In the case of high-density grid connection, the voltage increase will be higher than in a stand-alone grid connection system. To prevent overvoltage on the power distribution lines, the PV system's output will be restricted if the voltage of the power distribution line is close to the upper limit of the control range. Because of this interaction, the output loss will be larger in the high-density case. This research has developed a quantitative analysis method for PV system output and losses in order to clarify the behavior of grid-connected PV systems. All the measured data are classified into loss factors using a 1-minute average of 1-second data instead of the typical 1-hour average. The operation point on the I–V curve is estimated to quantify the loss due to the output restriction, using the module temperature, array output voltage, array output current, and solar irradiance. As a result, the loss due to output restriction is successfully quantified and the behavior of output restriction is clarified. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(2): 9–19, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20452
TL;DR: In this paper, the authors investigated the effect of number of voltage applications on puncture probability and partial damage caused by a small number of applied voltage applications before complete puncture occurred, and established an empirical equation relating to probability of puncture (P), impulse voltage (V) and number of V applications (N).
Abstract: Transmission and distribution lines are sometimes struck by lightning and there is some risk of electrical puncture of suspension insulators due to high and steep lightning surge voltage. When the insulators suffer from steep lightning surge voltages, the solid insulating body of the insulators sometimes is punctured before external flashover in the air occurs. These characteristics were investigated on the insulators in the laboratory by using different steep impulse voltages.
From the investigation results, both V-t characteristics of external flashover and internal puncture were obtained on the insulators. It was found that the puncture of the insulators is a matter of probability, depending on the dimensions of the insulators, steep impulse voltages and number of impulse voltage applications. Especially, the effect of number of voltage applications on puncture probability was clarified and partial damage by a small number of voltage applications was verified before complete puncture occurred. Based on the study results, an empirical equation relating to probability of puncture (P), impulse voltage (V) and number of voltage applications (N) was established.
TL;DR: In this article, the robust optimum design of SAW filters is formulated as a constrained optimization problem, and a penalty function method combined with an improved variable neighborhood search is proposed and applied to the problem.
Abstract: In order to increase the reliability of surface acoustic wave (SAW) filters, a robust optimum design technique is presented. The frequency response characteristics of SAW filters are governed primarily by their geometrical structures, that is, the configurations of the interdigital transducers (IDTs) and reflectors fabricated on piezoelectric substrates. To choose desirable structures of SAW filters through computer simulation, conventional design techniques utilize the equivalent circuit model of the IDT. However, they have rarely considered the accuracy of the underlying model, which may be degraded by the dispersion of the circuit parameters. In this paper, considering the errors of these parameters, the robust optimum design of SAW filters is formulated as a constrained optimization problem. Then, a penalty function method combined with an improved variable neighborhood search is proposed and applied to the problem. Computational experiments conducted on a practical design problem of a resonator type SAW filter demonstrate the usefulness of the proposed method. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(3): 45–54, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20469