Numerical Simulation of Power Generation Characteristics of a Disk MHD Generator with High‐Temperature Inert Gas Plasma

The power generation characteristics of a disk magnetohydrodynamics (MHD) generator with high‐temperature inert gas (argon) plasma have been examined by a time‐dependent two‐dimensional numerical simulation. The numerical simulation results based on the experimental conditions show that the enthalpy extraction ratio (= electrical output power/thermal input) can reach above 10%, which surely supports the reasonability of the experimental results. Proper selection of working conditions, especially the inlet total gas temperature, is necessary, since the gas temperature dominantly determines the electrical conductivity in the generator, unlike the conventional seeded plasma MHD generator. It is also found that the plasma is not in the recombination process but in the ionization process, where the ionization degree moderately increases along the flow. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(3): 23–30, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21237     

Performance Comparison of Scramjet‐Driven Experimental DCW‐MHD Generators with Different Cross‐Sections

The purpose of this study is to examine the influence of the shape of the cross‐section of a scramjet engine‐driven experimental diagonal conducting wall (DCW)‐MHD generator on generator performance by three‐dimensional numerical analyses. We have designed MHD generators with symmetric square and circular cross‐sections, based on an experimental MHD generator with an asymmetric square cross‐section. Under the optimum load conditions, the electric power output reaches 26.6 kW for the asymmetric square cross‐section, 24.6 kW for the symmetric square cross‐section, and 22.4 kW for the circular cross‐section. The highest output is obtained for the experimental generator with the asymmetric square cross‐section. The difference in the electric power output is induced by the difference of flow velocity and boundary layer thickness. For the generator with the asymmetric square cross‐section, the average flow velocity is highest and the boundary layer is thinnest. The compression wave is generated with dependence on the channel shape. The difference in the flow velocity and boundary layer thickness is induced by the superposition of the compression wave. © 2014 Wiley Periodicals, Inc. Electr Eng Jpn, 187(2): 9–16, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22403     

Three‐dimensional numerical analysis of a liquid metal MHD generator

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     

Behavior of magneto‐acoustic waves in a nonequilibrium subsonic disk MHD generator

The behavior of magneto‐acoustic waves in a nonequilibrium subsonic disk MHD generator was examined. The solution of the sixth‐order dispersion relation obtained by linearizing the set of MHD equations suggested that a magneto‐acoustic wave which propagates at a velocity of u_r ? a(u_r: radial fluid velocity, a: sound velocity) should be damped in subsonic flow. From time‐dependent quasi‐one‐dimensional simulations, it was verified that the pressure disturbance in the subsonic generator was damped at approximately the same rate as the value predicted by the linear theory. From a simplified analytical model, the mechanism of magneto‐acoustic instability with fully ionized seed was discussed, and the damping criterion for the magneto‐acoustic wave was clarified. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 142(4): 20–26, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10108     

Numerical performance simulation of frozen helium plasma disk MHD generator

MHD electrical power generation with frozen helium plasma (FHP) is examined numerically. The FHP can be initiated by preionized helium without the alkali metal seed at the generator inlet. Since the three‐body recombination coefficient of helium ions is low at electron temperatures above 5000 K, the ionization degree can be kept almost constant in the entire region of the generator channel. The r?θ two‐dimensional numerical results show that the performance of the FHP MHD generator is comparable to that of the seeded plasma MHD generator, if the additional power consumed to preionization is ignored. In the FHP MHD generator, the ionization degree at the inlet should be controlled precisely, as well as the seed fraction in the seeded plasma MHD generator. Under an adequate inlet ionization degree for sustaining the FHP plasma, the plasma maintains the uniform structure. On the other hand, a slightly excess ionization degree causes a strong Lorentz force in the upstream region of the generator, deteriorating the generator performance. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 26–33, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10030     

Combined carbon‐dioxide‐capturing high‐performance power generation system using a solid oxide fuel cell operating on pressurized fuel/air

The authors recently proposed a high‐performance combined carbon‐dioxide‐capturing power generation system using a solid oxide fuel cell (SOFC) and a closed‐cycle MHD generator, in which pure oxygen is used as the oxidant. This combined system makes the best use of the advantages of combustion with pure oxygen but fails to prevent the efficiency deterioration caused by high power demand for oxygen production. In the present study, the authors modified this previous system and proposed an improved combined carbon‐dioxide‐capturing power generation system using SOFC/MHD characterized by a higher overall thermal efficiency. In this system, pure oxygen is supplied only to the combustor to reduce the power required for the oxygen production, and pressurized air is used as the oxidant gas in the SOFC. The power saving amounts to about 5% of the thermal input, resulting in a very high total thermal efficiency of 67.53% (HHV) or 74.94% (LHV), which is considered to be the highest possible value of the overall thermal efficiency of carbon‐dioxide‐capturing systems. Advantages of the proposed system suggest that it is advisable to continue further research in this direction. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(4): 21–30, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20010     

Design of a 1‐GSample/s 9‐b double sampling track‐and‐hold amplifier in BiCMOS technology

This paper gives a detail presentation of a fully pseudo‐differential open‐loop BiCMOS track‐and‐hold amplifier (THA) for 9‐b operation up to 1 GSample/s. The proposed THA not only uses a double sampling technique to increase the achievable sampling frequency by a factor of two, but also employs a linearization technique to reduce the gain dependence of the THA input stage upon the input level. Moreover, timing mismatch between the clock signals of the two interleaved paths is minimized by means of a timing mismatch insensitive clock generator controlled by a common master sampling clock. The post‐layout simulation results using TSMC 75 GHz f_T, 0.35‐µm SiGe BiCMOS technology show that the proposed architecture achieve a signal to noise and distortion ratio of 53.92 dB, equivalent to the effective number of bits of 8.66‐b for 58.11 MHz input frequency at 1 GSample/s. The power dissipation of the whole THA is 161.1 mW. Copyright © 2012 John Wiley & Sons, Ltd.     

Switched‐capacitor‐voltage‐multiplier boost DC–AC inverter with adaptive stages

A multistage switched‐capacitor‐voltage‐multiplier inverter (SCVMI) is proposed with a variable‐conversion‐ratio phase generator and a sinusoidal pulse‐width‐modulation controller for boost DC–AC conversion and high‐efficiency regulation. Its power unit contains: SCVM booster and H‐bridge. The SCVM booster includes two m_c‐stage switched‐capacitor cells and two n_c‐stage switched‐capacitor cells in the interleaving operation to realize DC–DC boost gain of m_c × n_c at most. Here, the variable‐conversion‐ratio phase generator is suggested and adopted to change the running stage number and topological path for a suitable gain level of m × n (m = 1, 2, ?,m_c, n = 1, 2, ?,n_c) to improve efficiency, especially for the lower AC output. The H‐bridge is employed for DC–AC conversion, where four switches are controlled by sinusoidal pulse‐width‐modulation not only for full‐wave output but also for output regulation as well as robustness to source/loading variation. Some theoretical analysis and design include: SCVMI model, steady‐state/dynamic analysis, conversion ratio, power efficiency, stability, capacitance selection, output filter, and control design. Finally, the closed‐loop SCVMI is simulated, and the hardware circuit is implemented and tested. All the results are illustrated to show the efficacy of this scheme. Copyright © 2011 John Wiley & Sons, Ltd.     

A high‐speed reclosing method to improve the stability in a power system

This paper proposes a high‐speed reclosing operating method to improve the stability in a power system. The proposed method calculates the reclosing time, taking a standard case in which the reclosing is not done using the generator phase angle δ, and the angular velocity ω, and the field system voltage ed′. Also, the execution of reclosing time is calculated, while taking into consideration the acceleration/deceleration energy of the generator during a fault. It can be expected that δ is suppressed by this optimum reclosing operation. Therefore, the system stability can be expected to improve by carrying out high‐speed reclosing when a fault occurs. At present, it has been set at a value which seems to be optimal considering various problems in the reclosing time. However, in those methods, the system stability improvement effect cannot be expected. It was demonstrated that the high‐speed reclosing method serves to depress δ in the computer simulation. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(2): 13–21, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10317     

A very low complexity IR‐UWB transmitter with BPSK modulation for balanced antenna

A very low complexity impulse radio‐ultrawideband (IR‐UWB) transmitter suitable for balanced antenna is presented. This all‐digital transmitter employs the binary phase‐shift keying (BPSK) modulation scheme and eliminates the need for a balun. Also, a new Gaussian monocycle pulse generator is proposed which is used as impulse transmitted signal. The transmitter circuit was designed in 0.18‐μm complementary metal–oxide–semiconductor technology. The post‐simulation results show that the core chip size was only 0.02 mm². The output amplitude pulse yielded 150 mV peak‐to‐peak under a supply voltage of 1.8 V. Simulation results show that the transmitter consumes 8.5 pJ/pulse for 200‐MHz pulse repeating frequency. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Memristor‐based pseudo‐random pattern generator using relaxation oscillator

This letter presents a new pseudo‐random pattern generator using a memristor and relaxation oscillator based on an operational amplifier. The pulse width of the proposed generator is determined by the resistance storage property of the memristor, and the random pulse sequence depends on the RC time constant of the relaxation oscillator. From the simulation results, we show that the pulse width time is 7.6 μ s, and the random pulse sequence is 2048 bits. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

The effect of an externally applied radio‐frequency electromagnetic field on the performance of a disk MHD generator

The effects of an externally applied radio‐frequency (rf) electromagnetic field on the nonequilibrium performance of a disk MHD generator were examined experimentally. As a preliminary experiment, plasma production by the applied rf electromagnetic field was attempted in the disk generator (Disk‐PIA), in which rf induction coils were embedded in the one‐side disk wall, under the conditions of no seeding, no flow, and no magnetic field. From the results of the preliminary experiment, it was confirmed that the argon plasma (～110 Torr) was produced uniformly in the azimuthal direction by the rf electromagnetic field even in the presence of exposed anodes in the faced disk wall and metallic support at the disk center. In MHD power generation experiments with the Disk‐PIA installed in the shock‐tube facility, the increase in the electrical output and more indiscrete discharge attributed to the rf electromagnetic field were verified with good reproducibility for the first time. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(4): 46–53, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10009     

Absorbing boundary conditions for the FD‐TLM method : the perfectly matched layer and the one‐way equation technique

This paper investigates the absorbing boundary conditions for the frequency domain transmission line matrix method. Two approaches are presented, namely the perfectly matched layer (PML) technique and the one‐way wave equation. Concerning the PML technique, two‐dimensional and three‐dimensional transmission line matrix (TLM) nodes, already used in time domain, are exploited in frequency domain where a rigorous formulation of these PML–TLM nodes is presented. In addition, two types of one‐way wave operators are also transposed from time to frequency domain TLM approach: Taylor expansion and Higdon's boundary conditions. The simulation of a wideband matched load WR‐28 rectangular waveguide is presented for validation. Excellent results are obtained with a very thin PML layer. Results concerning one‐way operator techniques also show very good return loss performances. For instance, Higdon's boundary condition was extended beyond third‐order approximation, and a return loss better than 160 dB was obtained. Copyright © 2013 John Wiley & Sons, Ltd.     

Calculation of sudden three‐phase short‐circuit current of turbine generators by 3D magnetic field analysis

Sudden three‐phase short‐circuit current of a turbine generator was calculated by a three‐dimensional magnetic field analysis. That analysis takes into account the rotation, magnetic saturation, and eddy current at a rotor part. To compare test results and calculated results, a method was proposed for short‐circuit phase estimation at sudden three‐phase short‐circuit test by line voltage waveform of the test results. The calculated results of short‐circuit current waveform are in good agreement with the test results. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(1): 54–62, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20110     

A novel robust current control approach using adaptive line enhancer for three‐phase current‐source active power filter

An effective system control method is presented for applying a three‐phase current‐source PWM converter with a deadbeat controller to active power filters (APFs). In the shunt‐type configuration, the APF is controlled such that the current drawn by the APF from the utility is equal to the current harmonics and reactive current required for the load. To attain the time‐optimal response of the APF supply current, a two‐dimensional deadbeat control scheme is applied to APF current control. Furthermore, in order to cancel both the delay in the two‐dimensional deadbeat control scheme and the delay in DSP control strategy, an Adaptive Line Enhancer (ALE) is introduced in order to predict the desired value three sampling periods ahead. ALE has another function of bringing robustness to the deadbeat control system. Due to the ALE, settling time is made short in a transient state. On the other hand, total harmonic distortion (THD) of source currents can be minimized compared to the case where ideal identification of the controlled system can be made. The experimental results obtained from the DSP‐based APF are also reported. The compensating ability of this APF is very high in accuracy and responsiveness although the modulation frequency is rather low. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 50–61, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20014     

Numerical simulation of intermediate‐temperature disk type seal‐less SOFC fed with partially reformed methane

Since natural gas containing methane as major component is the most promising fuel for the solid oxide fuel cell (SOFC), development of a numerical simulation code of the intermediate‐temperature disk‐type seal‐less SOFC for methane fuel case is considered to be very useful. In this study, therefore, we develop a new simulation code for the single cell unit of this type of SOFC fed with partially reformed methane as the fuel gas, based on the existing simulation code for pure hydrogen. We calculate the current density versus single cell voltage (i–V ) curves of the single cell unit for various cases with a wide range of the cell temperature and prereformer temperature conditions and compare them with the corresponding experimental results. From the results, we confirm that the numerically obtained i–V curves coincide very well with the corresponding experimental ones in all cases. The variations of the i–V curves, which depend not only on the cell temperature but also on the prereformer temperature, are successfully simulated with a sufficiently high accuracy, indicating the validity of the newly developed simulation code. We also investigate the detailed influence of the cell temperature and prereformer temperature on the cell performance on the basis of the numerically obtained gaseous partial pressure profiles in the fuel channel and Nernst potential profiles in the cell, and clarify the reason why the prereformer temperature has obvious influence on the cell performance when the cell temperature is low, though the cell performance is almost independent of the prereformer temperature when the cell temperature is high. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Two‐dimensional numerical simulation on performance of liquid metal MHD generator

The performance of a liquid metal MHD generator is investigated with a two‐dimensional numerical simulation. The effects of the electrode length, the position of current lead connection, and the insertion of an insulator on the performance are examined taking account of the current flow in the electrode. There exists an optimal electrode length for a given distribution of applied magnetic flux density. For a short electrode, the efficiency decreases because the power output becomes small. For a long electrode, on the other hand, the efficiency also decreases owing to the leakage current from the upstream and downstream edges of the electrode. An optimal current lead position was revealed. This fact is ascribed to the distributions of induced magnetic field and the current flow in the electrode. It was found that insertion of the insulator is effective for improving the performance, by which the eddy current can be reduced. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(1): 25–32, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ eej.20165     

Plasma Behavior in a High‐Temperature Noble Gas Plasma Disk‐Shaped MHD Power Generator

R‐θ two‐dimensional numerical simulations have been carried out to clarify the plasma behavior in a high‐temperature noble gas plasma disk‐shaped magnetohydrodynamic (MHD) generator. At low inlet total temperature and high load resistance, the plasma has spiral structure which is similar to the nonuniform structure under the weak noble gas ionization condition in a seed‐plasma MHD generator. As seen in a linear‐shaped Faraday‐type MHD generator, the plasma becomes stable with increase in the inlet total temperature because the coulomb collision of electrons becomes dominant. Even at low inlet total temperature, the ionization instability can be suppressed for low load resistance, because the relatively low electron temperature due to less Joule heating makes the ionization relaxation time longer than plasma residential time.     

Stability and H∞ performance of multiple‐delay systems with successive delay components

This paper presents a new model for linear time‐delay systems with multiple delayed states where each delay contains finite number of successive components with different time‐varying properties, referred to as multiple‐delay system with successive time‐varying delay components (MDSSTDCs). General stability result and H_∞ performance conditions, under which the MDSSTDCs are asymptotically stable with certain H_∞ disturbance attenuation level, are derived by exploiting a general Lyapunov–Krasovskii functional and by making use of novel techniques for time‐delay systems. The result is applied to two special types of time‐delay systems frequently used in engineering applications and corresponding conditions for stability and H_∞ performance are obtained. Copyright © 2010 John Wiley & Sons, Ltd.