Fast DC Research Articles

Direct connection of WECS system to the MV grid with multilevel converters

A medium voltage power interface for a variable speed Wind Turbine is presented in this paper. The converter topology consists on the Back-to-Back connection of two medium voltage Diode Clamped Multilevel Inverters ( DCMI) in the full power path. This mitigates traditional tradeoffs around the low voltage connection between the generator and the grid on the megawatt range. Also, this configuration allows for higher control versatility for grid codes compliance. The converter controllers are based on a Finite-States Model Predictive Control approach, leading to fast dynamic response and DC bus voltage equalization. The control scheme can be used with converters of an arbitrary number of levels with reduced computational effort. This is based on necessary switching restrictions which allow the reliable operation of converter legs. The performance of the control scheme is evaluated through computer simulations.

Power Loss Comparison of Single- and Two-Stage Grid-Connected Photovoltaic Systems

This paper presents power loss comparison of single- and two-stage grid-connected photovoltaic (PV) systems based on the loss factors of double line-frequency voltage ripple (DLFVR), fast irradiance variation + DLFVR, fast dc load variation + DLFVR, limited operating voltage range + DLFVR, and overall loss factor combination. These loss factors will result in power deviation from the maximum power points. In this paper, both single-stage and two-stage grid-connected PV systems are considered. All of the effects on a two-stage system are insignificant due to an additional maximum power point tracker, but the tracker will reduce the system efficiency typically about 2.5%. The power loss caused by these loss factors in a single-stage grid-connected PV system is also around 2.5%; that is, a single-stage system has the merits of saving components and reducing cost, and does not penalize overall system efficiency under certain operating voltage ranges. Simulation results with the MATLAB software package and experimental results have confirmed the analysis.

Control design for an inductions machine based 42v integrated starter alternator

An improved implementation of an induction machine-based integrated starter alternator. This article presents a complete control design of an induction machine-based integrated starter alternator (ISA) for future 42-V PowerNet. The article also discusses the design of a fast dc voltage controller and field-weakening control to achieve the challenging requirements of ISA application.

1 V and 10 V SNS Programmable Voltage Standards for 70 GHz

Programmable Josephson voltage standards (PJVSs) in combination with fast switchable DC current sources have opened up new applications in the field of low-frequency AC metrology. The growing interest in output voltages of up to plusmn10 V initiated efforts by several National Metrological Institutes to realize 10 V PJVSs. Presently, only 10 V PJVSs from PTB based on SINIS junctions have been successfully incorporated into existing setups for AC metrology. However, the fabrication of 10 V SINIS arrays that are driven at 70 GHz suffers from very low yield. The recent technological progress made at NIST enabled the drop-in replacement of the low-yield SINIS arrays by more robust SNS arrays. The N-material is an amorphous NbxSi1-x alloy near the metal-insulator transition and is deposited by co-sputtering. For the first time, fully operational 1 V and 10 V PJVSs with SNS junctions that are suitable for a 70 GHz drive have been fabricated and tested. This work was done in close cooperation between NIST and PTB.

Measurement of singlet oxygen concentrations in a fast flow dc discharge in oxygen–argon mixtures

Production of singlet delta oxygen (SO) by a dc glow discharge in flowing O2 : Ar mixtures has been investigated. SO concentrations have been measured with dilution of oxygen up to O2 : Ar = 5 : 95 at a pressure up to 14 Torr and specific power load in the discharge up to 50 J mmol−1. The largest relative SO concentrations achieved in experiments exceeded 9%. This is sufficient to obtain population inversion and laser gain in the oxygen–iodine medium.It was found that for the mixtures with large Ar content stray spectral lines appear near the SO 1268 nm band that is used to determine the SO concentration. These are the Ar I lines and their intensities increase relative to the SO band with Ar content. To estimate their contribution it is suggested to normalize their intensities on the intensity of the 1280 nm line.

Influence of a Fast Electron Component on the Plasma Sheath Structure at the Inside of the Tunnel Probe

AbstractThe possible influence of a small population of suprathermal electrons on the tunnel probe, a new kind of Langmuir probe for fast DC measurements of ion flux and electron temperature in the tokamak scrape‐off layer, has been investigated by numerical simulations. It was found that suprathermal electrons can influence the ion current distribution over the inner plasma collecting surfaces of the tunnel probe, and thus influence tunnel probe Te measurements. The ion current distribution depends on the structure of the Debye and the magnetic sheath inside the tunnel probe. Therefore, we make here a first attempt at investigating the influence of suprathermal electrons on the scaling of those sheaths. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Detailed Analysis of the Electron-Transfer Properties of Azurin Adsorbed on Graphite Electrodes Using dc and Large-Amplitude Fourier Transformed ac Voltammetry

The analysis of dc cyclic voltammograms of surface-confined metalloproteins is complicated by large background currents, significant ohmic iRu drop, and frequency dispersion related to protein and electrode surface inhomogeneity. The use of large-amplitude Fourier transform ac voltammetry for the quantification of the electron-transfer properties of a thin film of redox-active protein azurin adsorbed onto edge-plane, basal-plane, and highly oriented pyrolytic graphite electrode surfaces has been evaluated and compared to results obtained by dc cyclic voltammetry. In principle, it has been established that fourth and higher harmonic sine-wave data are ideally suited for analysis of electron-transfer processes as they are almost completely devoid of background capacitance current contributions. However, uncompensated resistance has a higher impact on these components, as is the case with fast scan rate dc techniques, so strategies to include this term in the simulations have been investigated. Application of recommended strategies for the evaluation of the electron-transfer properties of azurin adsorbed onto three forms of graphite, each having different background or uncompensated resistance values, is described and compared to results obtained by traditionally used forms of cyclic voltammetry. The electron-transfer rate constant, k0', of azurin at a highly oriented pyrolytic graphite electrode surface was approximately 250 s(-1), compared with > or =1000 s(-1) at edge-plane and basal-plane graphite electrodes. The significantly lower k0' value found at the highly oriented pyrolytic graphite electrode was related to the relatively low level of edge-plane defect sites present at the surface of this electrode. However, analysis of high ac harmonics suggests that frequency dispersion is substantial at all electrode surfaces. Such effects in these diffusionless situations are significantly enhanced relative to solution-phase voltammetry, where overlay of diffusion layers minimizes the impact of heterogeneity.

Sensitivity of electron temperature measurements with the tunnel probe to a fast electron component

The tunnel probe is a new kind of Langmuir probe for fast dc measurements of ion flux and electron temperature in the tokamak scrape-off layer. The probe is calibrated using two-dimensional kinetic analysis of the ion current distribution on the concave conductors. Though qualitative agreement with classical Langmuir probe measurements was found, the electron temperature given by the tunnel probe is several times lower. One possible explanation might be an overestimation of the electron temperature by the Langmuir probe, due to a non-Maxwellian electron velocity distribution which can be modelled in a first approach as a two-temperature distribution. Hence the possible influence on the tunnel probe of a small population of nonthermal electrons is investigated by means of the two-dimensional kinetic code XOOPIC. It is found that this influence can be seen as the result of two combined physical effects: nonthermal electrons will reach the back plate (BP) and the ion current distribution over tunnel and the BP will change. The resulting dependence on probe bias and parallel ion current density of the TP sensitivity to nonthermal electrons is not reflected in CASTOR measurement results. Thus nonthermal electrons on their own cannot fully explain the discrepancy between Langmuir and tunnel probe measurements.

Quench Protection System for the Superconducting Coil of the KSTAR Tokamak

This paper presents two-stage high-power mechanical-thyristor switches developed as 40-kA direct current (dc) circuit breakers for the superconducting coil energy dump system of Korea superconducting Tokamak advanced research (KSTAR). An advanced switching system used in the quench protection should allow multishot mode of operation without maintenance and long lifetime with arcless dc current commutation. The system is designed to combine the advantages of the both mechanical and solid-state power switches. The mechanical stage is to conduct dc current for normal superconducting coil operation and the thyristor stage is to provide fast arcless dc current interruption for quench protection (QP). Compared with the all solid-state switches and vacuum interrupters of equal capabilities the proposed switch is much cheaper than the dc breakers and has lower power dissipation in current conducting state Kuchinski in Proc. Power Ele., 899-903, 1995; Benfatto IEEE Power Del., Vol. 3, No. 4, pp. 1372-1376, Oct. 1998. Also, it is much faster than the vacuum interrupters. The system is designed to break 40-kA dc current within 200 ms. Also, KSTAR device, a configuration of the energy dump system and coil power supplies are presented

Ultra-low-drift and very fast dc SQUID readout electronics

High-slew rate and thermo-stable readout electronics for dc superconducting quantum interference devices (SQUIDs) is presented. This electronics represents an optimum combination of the most important parameters for the SQUID-system user. In the new flux-locked loop (FLL) - unit design we have decreased a voltage white noise level down to the 0.32 nV/Hz½, with a flicker noise corner frequency of ∼0.1 Hz. By making use of electro-thermal feedback in the first stage amplifier, and multi-loop conventional feedback throughout the whole amplifier we have achieved a very low thermal drift <10 nV/K for T = 20 - 65 °C. FLL gain stability is improved down to ∼1% for the temperature range 10 - 60 °C and for 5 V (peak-peak) ± 30% of the power supplier voltage range. The maximum gain bandwidth product of the FLL-unit was increased 10 times up to ∼5 GHz. In turn, we could reach more than 10 Mϕ0/s slew rate while using a conventional LTS SQUID (connected to the FLL by a 1.2 meterlength twisted pair), with a maximum voltage of the field-to-flux transfer function of ⩾60 µV (peak-peak). At the same time, we reduced by 40% the number of chips used in the FLL unit.

Simultaneous measurements of fluctuations of ion current, electron temperature, and floating potential with a tunnel probe

The tunnel probe is a new kind of Langmuir probe for use in the tokamak scrape-off layer. Two-dimensional kinetic analysis of the ion current distribution on the concave conductors is used to calibrate the probe for making fast dc measurements of ion flux and electron temperature. Qualitative agreement with classical Langmuir-probe measurements is found, but the electron temperature given by the tunnel probe is several times lower. This discrepancy is partly caused by secondary electron emission, and can easily be corrected. Strong eduction of ion-flux and electron-temperature fluctuations is observed during electrode biasing.

Generation of Cytotoxic T Cell Responses Directed to HLA Class I Restricted Epitopes from the Aspergillus f16 Allergen.

Invasive pulmonary aspergillosis is a primary cause of morbidity and mortality in immunocompromised patients such as hematopoietic progenitor cell transplant patients. Studies both in patients with allergic bronchopulmonary aspergillosis and murine models demonstrated the importance of a CD4+ Th1 T cell response in conferring protection from infection or preventing disease progression. The role of CD8+ T cell response to A. fumigatus is less clear. Our efforts to develop effective immunotherapeutic approaches against A. fumigatus included preparation of 104 overlapping pentadecapeptides spanning the 427 aa coding region of the aspergillus allergen, Asp f16 previously shown to induce T cell responses. Each 15 aa peptide overlaps the preceding peptide by 11 aa. Monocytes from healthy donors were treated with GM-CSF and IL-4 for 2-3 days to generate immature dendritic cells (fast DC), pulsed with a pool containing 1 μg of each pentadecapeptide, then matured with inflammatory cytokines (IL-1β, IL-6, PGE2 and TNF-alpha) for 2 days. Mature, pulsed fast DC were used to prime proliferative and CTL responses (weekly primings). T cells from 5/5 donors proliferated to the peptide pool. CTL lines were obtained from each of the first two donors that were primed. After 4 weeks the line from donor #2 was strongly cytotoxic to autologous peptide pool-pulsed and aspergillus culture extract-pulsed DC and peptide pool pulsed HLA Class I matched BLCL. Supernatant from this line killed fresh aspergillus conidia. Six of 21 smaller pools of 4-11 peptides showed reactivity. Specificity could be narrowed by screening peptides shared by the pools to 3 candidate peptides. Pool-pulsed BLCL matched for only 1 or 2 HLA alleles were used to demonstrate CTL restriction by HLA-B-3501. A database search of peptides likely to be restricted to B3501 identified the likely sequences as YFKYTAAAL, LPLCSAQTW, and GTRFPQTPM. Each induced similar reactivity when pulsed onto B-3501+ targets. CD8+ T cells steadily increased from 5.2% at week 3 to 19.0% after the 7th priming. CTL activity and IFNγ production were exclusively mediated by CD8+ T cells and CD107a was expressed by 42% of the CD8+ T cells in response to pool-pulsed BLCL indicating degranulation. CTL cross-reacted with pool pulsed B3503+ BLCL but not B3502+, or B3508+ BLCL. B3503+ BLCL presented YFKYTAAAL and to a lesser extent GTRFPQTPM but not peptide LPLCSAQTW. Our data show that DC pulsed with a pentadecapeptide pool from Asp f16 are capable of inducing a CD8+, HLA-Class I restricted Aspergillus-specific T cell response directed to multiple peptides contained within the pool. Further characterization of this system is in progress to identify additional immunogenic peptides from Asp f16 that might be useful in clinical immunotherapy protocols to prime protective immune responses to prevent or treat aspergillus infection.

Generation of Th1 T Cell Responses Directed to a HLA Class II Restricted Epitope from the Aspergillus f16 Allergen.

Invasive pulmonary aspergillosis is a primary cause of morbidity and mortality in immunocompromised patients, including hematopoietic progenitor cell transplant patients. Studies in patients with allergic bronchopulmonary aspergillosis as well as murine models have demonstrated the importance of a CD4+ Th1 T cell response in conferring protection from infection or preventing disease progression. A. fumigatus allergens have been identified based on reactivity to IgG and IgE antibodies in serum from patients with allergic bronchopulmonary aspergillosis. One allergen, Asp f16 was shown to induce a protective Th1 T cell response to infection with aspergillus conidia in murine studies. We prepared a series of 104 overlapping pentadecapeptides spanning the entire 427 aa coding region of Asp f16. Each 15 aa peptide overlaps the preceding peptide by 11 aa. Autologous monocytes from healthy donors were treated with GM-CSF and IL-4 for 2–3 days to generate immature dendritic cells (fast DC), pulsed with a pool containing 1 μg of each pentadecapeptide, then matured with inflammatory cytokines (IL-1β, IL-6, PGE2 and TNF-α) for 2 days. Mature, pulsed fast DC were used to prime proliferative and CTL responses (weekly primings). T cells from 5 of 5 donors proliferated to the peptide pool. CTL lines were obtained from each of the first two donors that were primed. As early as 3 weeks the T cell line from donor #1 had a high frequency of IFNγ-producing CD4+ T cells (24.5±5.4%) in response to the peptide pool, was cytotoxic to autologous peptide pool-pulsed and aspergillus culture extract pulsed DC, and peptide pool pulsed autologous BLCL. Supernatant from this culture killed fresh aspergillus conidia. Screening of 21 smaller pools containing 4–11 peptides showed reactivity to three smaller pools and could be narrowed by screening individual peptides shared by the pools to a single candidate sequence of TWSIDGAVVRT that elicited IFNγ production and lytic activity equal to the entire pool. Peptide pulsed BLCL matched with the donor for only 1 or 2 HLA alleles were used to demonstrate that CTL activity and IFNγ production was restricted by HLA-DRB1- 0301. 23% of the CD4+ cells in the culture expressed CD107a in response to peptide pool indicating degranulation. PBMC from DRB1-0301+ individuals proliferated strongly in response to peptide TWSIDGAVVRT. Our data show that DC pulsed with a pentadecapeptide pool from Asp f16 are capable of inducing a CD4+, HLA-DR-restricted aspergillus-specific Th1 type T cell response directed to a single peptide contained within the pool. Further characterization of this system is in progress to identify other immunogenic peptides from Asp f16 that might be useful in clinical immunotherapy protocols to prime protective immune responses to prevent or treat aspergillus infection.

Artificial Intelligent Controller for Current Source Converter-Based Modular Active Power Filters

The control methodology of the active power-line filter is the key element for its successful performance in mitigating the line current harmonics. The control system processes the distorted line current signal and forces the converter to inject the proper compensating current. At the same time, it regulates the dc term, i.e., the dc current in the current source converter topology and the dc voltage in the voltage source converter topology. In this paper, a new intelligent control scheme for a modular single-phase active power filter based on the current source converter (CSC) topology is proposed. The intelligent controller utilizes two adaptive linear neurons (ADALINEs) to process the signals obtained from the power-line. The first ADALINE (the Current ADALINE) extracts the harmonic components of the distorted line current signal and the second ADALINE (the Voltage ADALINE) estimates the fundamental component of the line voltage signal. The outputs of the two ADALINEs are used to construct the modulating signals of a number of CSC modules, each dedicated to eliminate a specific harmonic. The proposed controller is also responsible for activating selected CSC filter module(s) to the electric grid. The automated activation of the corresponding filter module(s) is based on the decision-making rules in accordance with the current total harmonic distortion (THD/sub i/) and the harmonic factor (HF) levels set by the IEEE 519-1992 standard. A special 3-level PWM switching strategy is proposed for the filter modules which results in a 50% reduction in the overall switching losses compared with the 2-level method. The proposed controller adjusts the I/sub dc/ in each CSC module based on the present magnitude of the corresponding harmonic current which results in optimum dc-side current value and minimal converter losses. The high speed, accuracy, efficiency and flexibility offered by the proposed controller, combined with the fast response and low dc energy storage requirement of CSC topology, are the main advantages of the proposed active filter system. The analytical expectations are verified by digital simulation using EMTDC simulation package.

Free evolution of superposition states in a single Cooper pair box

We have fabricated a single Cooper-pair box (SCB) in close proximity to a single electron transistor (SET) operated in the radio-frequency mode (RF-SET) with an inductor and capacitor lithographed directly on chip. The RF-SET was used to measure the charge state of the SCB revealing a $2e$ periodic charge quantization. We performed spectroscopy measurements to extract the charging energy ${(E}_{C})$ and the Josephson coupling energy ${(E}_{J}).$ Control of the temporal evolution of the quantum charge state was achieved by applying fast dc pulses to the SCB gate. The dephasing and relaxation times were extracted from these measurements.

Coherent dynamics of a Josephson charge qubit

We have fabricated a Josephson charge qubit by capacitively coupling a single-Cooper-pair box (SCB) to an electrometer based upon a single-electron transistor configured for radio-frequency readout (RF-SET). Charge quantization of 2e is observed and microwave spectroscopy is used to extract the Josephson and charging energies of the box. We perform coherent manipulation of the SCB by using very fast DC pulses and observe quantum oscillations in time of the charge that persist to ~=10ns. The observed contrast of the oscillations is high and agrees with that expected from the finite E_J/E_C ratio and finite rise-time of the DC pulses. In addition, we are able to demonstrate nearly 100% initial charge state polarization. We also present a method to determine the relaxation time T_1 when it is shorter than the measurement time T_{meas}.

The addition of H2 to an Ar plasma studied by fast flow glow discharge mass spectrometry (FFGD-MS): mechanism and relative sensitivities

Changes in steel and copper cathode ion intensities from the afterglow of a fast flow dc glow discharge (FFGD) have been studied as a function of the amount of H2 added downstream from the active discharge region. The signals from the majority of different elements increased, although some analytes were actually quenched. In general, the data were qualitatively similar to previous ‘hydrogen effect’ studies using conventional ‘static gas’ GD source designs. Here variations in the size of the effect are reported as hydrogen concentration, plasma density, interaction time and ion extraction voltage were changed independently. It was not possible to rationalise the data obtained using a mechanism based on ion–molecule reactions. The results also indicated that Penning ionisation involving the Ar 3P2,0 states is probably not the primary mechanism for the ions detected in this kind of flowing plasma. On the other hand, a mechanism based on the Rydberg gas model of the flowing plasma [R. S. Mason, P. D. Miller, I. P. Mortimer, D. J. Mitchell and N. A. Dash, Phys. Rev. E, 2003, 68, 016408] fits well with all the changes observed.

A low-cost test solution for wireless phone RFICs

This article describes an IBM approach for testing high-volume, complex RFICs at a fraction of the cost of the integrated circuit. This approach uses a personal computer, a fast benchtop dc parametric analyzer, and RF-to-analog circuits to test an RFIC during the manufacturing process. The described system and methodology are specifically designed for high-volume test, where test cost is extremely important; they are not recommended for lower-volume products (less than 1 million per month). This article describes the system architecture and discusses design, maintenance, and implementation considerations. The system is designed to reduce the cost of a complex RFIC manufacturing test to equal that of a discrete component, such as a resistor or capacitor. Given the relatively easy implementation and the drastic cost reduction associated with the test solution, this architecture establishes a new standard for the future of RF test. In fact, this architecture may result in the fastest RF tester currently available.

An evolutionary approach to automatic synthesis of high-performance analog integrated circuits

This paper presents an analog integrated circuit synthesis system based on an evolutionary approach. The system contains several novel features. One of these is the high-performance optimization algorithm, which is a combination of evolutionary strategies and simulated annealing. Modeling of dc parameters is done via a fast dc simulator developed for this purpose whereas modeling of ac parameters can be done either with user-defined equations or with neural-fuzzy performance models trained from SPICE simulations. Another novel feature of the system is the incorporation of matching properties of devices. This way, the optimized circuit becomes tolerant to process variations. The synthesis system has been tested on several independent examples and synthesized circuits have been verified functionally with SPICE simulations. Finally, a prototype chip composed of the three examples has been manufactured. The measurement results have demonstrated the validity of the synthesis system on silicon.

Deep-depletion high-frequency capacitance-voltage responses under photonic excitation and distribution of interface states in MOS capacitors

Probing the deep-depletion mode high-frequency capacitance-voltage (C-V) responses of MOS capacitors under photonic excitation, the distribution (D/sub it/) of the interface states (E/sub t/) at Si/SiO/sub 2/ heterojunctions was characterized. A photon energy E/sub ph/=0.943 eV (less than the silicon energy bandgap) was employed for the characterization of interface states in the photoresponsive energy band. In order to limit the photonic contribution to the change in the gate capacitance by excess carriers excited only from the interface states, a fast dc sweep rate (50 mV/s) with a high-frequency (500 kHz) small-signal was applied. Photonic C-V responses with a slow dc sweep for E/sub ph/=0.943 eV and a fast sweep for E/sub ph/=1.481 eV have been also provided for a comparison. Modulating the surface potential with the gate bias, a U-shaped distribution of D/sub it/ was obtained over the photoresponsive energy band in (E/sub C/-E/sub ph/)<E/sub t/<(E/sub i/-q/spl phi//sub f/+q/spl phi//sub s/) from NMOS and (E/sub i/+q/spl phi//sub s/-q/spl phi//sub f/)<E/sub t/<(E/sub V/+E/sub ph/) from PMOS capacitors. D/sub it,max/ was observed to be /spl sim/1.76/spl times/10/sup 11/ cm/sup -2/eV/sup -1/ on the edges of conduction and valence bands.