Sinusoidal AC Voltage Research Articles

One-Dimensional Modeling of Dielectric Barrier Discharge in Xenon

A 1-D fluid model coupled with an external circuit is proposed to study the Xe dielectric barrier discharge (DBD) under a 50-kHz ac sinusoidal voltage. The impact of ions and photons on barrier surfaces and the thermal motion of charged particles in the sheath are taken into account in this model. The spatial and temporal distributions of electrons, ions, and excited, resonance, and metastable particles are investigated. The experimental investigations on discharge current densities under different voltage source amplitudes are analyzed and compared with simulation results. The results reveal that, with the increment of voltage source amplitudes, the waveforms of gas gap voltage and discharge current all move forward the applied voltage, showing a gradually decreased phase shift, which is in good agreement with the experimental observations. The evolution of surface charges accumulated on dielectric barriers can be divided into six stages during an ac cycle, and they play a key role in the ignition and extinction of the discharge. It is concluded that, while the charge difference between the surfaces of a two-side dielectric is up to a certain value and the applied voltage is low enough, the gas breakdown will occur. The spatiotemporal variations of particle densities and electric field indicate that the Xe DBD under the conditions considered in this paper is a typical glow discharge. Furthermore, the electron emission brought by impact of photons on dielectric surfaces can accelerate gap breakdown and strengthen the intensity of the discharge, and the sheath phenomenon is more obvious under the consideration of thermal motion of charged particles in boundary conditions.

A novel approach for a sinusoidal output inverter

Minimization of the total harmonic distortion (THD) at the output of an inverter is essential to reach the ideal case, i.e. a pure sinusoidal. So far, very intensive studies about this topic have been carried out. In this study, a fully rectified version of a sinusoidal voltage waveform at an utility amplitude and frequency obtained from a well-known buck–boost regulator has been converted to a sinusoidal AC voltage waveform with a simple inverter operation. The purpose of this innovative circuit is to generate an approximate sinusoidal voltage waveform with a quite low THD at the inverter output without invoking the harmonic elimination techniques. Since distortions in the AC link voltage in this circuit fully depend on how well the capacitor current is regulated to its reference, the value of the load current is a critical component in this regulation.

새로운 변조방식을 사용한 단상 인버터 시스템

본 논문에서는 새로운 변조방식을 사용한 단상 인버터 시스템을 제안한다. 제안한 시스템은 buck-boost 변환기와 인버터로 구성되며 새로운 변조방식인 PWAM(Pulse Width/Amplitude Modulation)방식을 사용하여 제어한다. PWAM방식은 PWM(Pulse Width Modulation)방식과 PAM(Pulse Amplitude Modulation) 방식이 혼합된 새로운 변조방식이며 인버터의 입력단에 위치한 buck-boost 변환기는 일정한 직류전압을 입력으로 받아 가변 직류전압으로 변환한다. 인버터는 buck-boost 변환기에서 출력된 가변 직류전압을 입력으로 하며, PWM 구간에서는 PWM 스위칭을 하고 PAM 구간에서는 인버터가 스위칭을 하지 않음으로써 정현 교류전압으로 변환한다. 제안한 PWAM방식을 사용한 단상 인버터 시스템은 PAM 구간에서 스위칭 동작을 하지 않으므로 기존의 방식에 비해 스위칭 횟수가 감소하여 스위칭 손실을 줄일 수 있다.

Luminescent characteristics in blue-emitting Bi-activated multicomponent oxide phosphor thin films

The luminescent characteristics in developed blue-emitting Bi-activated multicomponent oxide phosphor thin films that are composed of various combinations of La2O3, Y2O3, and Gd2O3 as the host material are investigated; ((La2O3)1−X–(Gd2O3)X):Bi, (Gd2O3)1−Y–(Y2O3)Y):Bi, and ((Y2O3)1−Z–(La2O3)Z):Bi phosphor thin films were prepared on thick BaTiO3 ceramic sheets by either a conventional or a combinatorial rf magnetron sputtering deposition method using a powder target. The resulting phosphor thin films, which were prepared with various chemical compositions and postannealed above about 800 °C in an Ar gas atmosphere, all exhibited photoluminescent (PL) and electroluminescent (EL) emissions. However, the PL emission spectra observed from these phosphor thin films were considerably affected by the ultraviolet (UV) light used in the excitation. Intensive blue PL emissions were obtained in all of the phosphor thin films that were postannealed at 1050 °C and excited by an appropriate UV light. In comparison with the PL emission spectra, the EL emission spectra observed from thin-film electroluminescent (TFEL) devices fabricated using the Bi-activated multicomponent oxide phosphor thin films as the emitting layer exhibited a redshift of the emission band or an emergence of a new emission band accompanied by spectral broadening at longer wavelengths. In addition, high-luminance blue-green EL emissions were obtained in TFEL devices fabricated using the above phosphor thin films and driven by a sinusoidal wave ac voltage at 1 kHz.

Diode Junctions in Single ZnO Nanowires as Half-Wave Rectifiers

We introduce dopants in a section of ZnO vertical nanowires. This forms a junction in the nanowires that exhibit diode nature in current−voltage characteristics. Under sinusoidal ac voltage, the nanowires act as half-wave rectifiers. Operation of the rectifiers at high frequencies is restricted by a phase lag between current and applied ac voltage. We vary the length of the vertical nanowire junctions and study its effect on rectification characteristics. We find that the phase lag of current is less in shorter nanowire diodes than that in the longer ones. The shorter diodes hence operate until higher frequencies as half-wave rectifiers.

Ultraviolet-light-emitting AlN:Gd thin-film electroluminescence device using an energy transfer from Gd3+ ions to N2 molecules

An ultraviolet (UV)-light-emitting AlN:Gd thin-film electroluminescence device (TFELD) was demonstrated for application to flat-panel lighting. AlN:Gd thin films were deposited by rf magnetron sputtering at 200 °C and applied to an ac-voltage-driven TFELD with a double-insulating structure as an emission layer. UV-light emission was observed over a threshold voltage of 270 V for a 5 kHz sinusoidal ac voltage. Electroluminescence (EL) spectra were compared with photoluminescence and cathodoluminescence spectra of AlN:Gd originating from Gd3+ P6j→S87/2 transitions and with an emission spectrum of the second positive system (C3Πu→B3Πg) of N2 molecules. As a result, an energy transfer from Gd3+ P6j→S87/2 to N2 C3Πu→B3Πg is discussed as a likely mechanism for the UV EL. Finally, a preliminary result, associated with the conversion from UV light into blue-green light via a phosphor, is demonstrated for the color tunability of the TFELD.

Effects of ambient humidity and temperature on partial discharge characteristics of conventional and nanocomposite enameled magnet wires

Effects of ambient humidity and temperature on partial discharge (PD) characteristics in twisted pairs with conventional and nanocomposite enameled magnet wires have been investigated. Measurements of the PD inception voltage (PDIV) and the apparent PD charge were performed by applying an AC sinusoidal waveform voltage of 60 Hz to the twisted pair. The observed PDIV in this study can be classified into the following three behaviors. First, the PDIV in both wires decreases with increasing relative humidity (RH) at low temperature. Secondly, the PDIV in both wires slightly increases when increasing the RH at high temperature. Thus, there is a certain value of the absolute humidity to determine the lowest PDIV in both cases with the conventional and nanocomposite enameled wires. Thirdly, the PDIV in the conventional enameled wire significantly decreases at the RH of 95%, while the decrease rate of that in the nanocomposite enameled wire is relatively small. The observed PD phenomena are discussed in terms of material characterization of the enameled wires such as changes in permittivity due to moisture absorption and wettabilitiy under voltage application.

Microplasma array devices with coplanar electrodes operating in neon

Microplasma array devices with coplanar electrodes have been fabricated and operated in neon at pressures up to 684 Torr. The microcavity of the device is composed of a couple of electrodes instead of dielectric or single cathode. The experiment results for the line array with 12 microcavities driven by AC sinusoidal voltage show that the power loading of each microcavity reaches approximately several kW cm −3 and the luminance reaches 2500 cd m −2. The discharge delay time for the devices excited by AC pulse voltage is about 1–3 μs. The lighting patterns of the devices with address electrode validate the addressing ability of the proposed devices.

Modelling and simulation of a polymer electrolyte membrane fuel cell system with a PWM DC/DC converter for stationary applications

A polymer electrolyte membrane (PEM) fuel cell power system is a low voltage and high current power source that needs a DC/DC converter to boost the output voltage of the fuel cell system for high efficiency and better performance. The fuel cell power system can be connected, in parallel, to a grid via a voltage impressed pulse width modulation (PWM) converter that forms the DC source into a sinusoidal AC current and voltage. The system can be extended to supply not only active power, but also compensate reactive power by exploiting the energy stored in the capacitor. The paper proposes an integrated dynamic model for a PEM fuel cell system with a DC/DC PWM converter and the associated controls that can be used as a power source for a multifunctional compensator. Simulations are carried out to analyse the interactive effects of load currents on the components of the fuel cell power system. The electric load currents applied for the DC converter are obtained from the instantaneous power balance between the DC and the AC side of the AC/DC converter, where the AC currents generated are different currents derived by using a power theory from typical three-phase square waveforms on a grid. Included are also effects of the DC capacitance on the DC voltage variation at load currents applied. Integrated approach reveals a variety of possibilities to analyse and study interacting effects of electric loads on parameters of the fuel cell system components.

Evaluation of High Frequency Switching Capability of SiC Schottky Barrier Diode, Based on Junction Capacitance Model

An SiC power device possesses features like high breakdown voltage, fast switching capability, and high temperature operation, and is expected to be superior to conventional Si power devices. This paper clarifies the switching capability of an SiC Schottky barrier diode (SBD) in rectification of high frequency ac voltage. The dynamic behavior of the SiC SBD for switching operation is modeled based on semiconductor physics and device structure, and is characterized by its dc current-voltage (I-V) and ac capacitance-voltage (C-V) characteristics. A C-V characterization system, which measures capacitance using a dc bias voltage corresponding to the maximum rated voltage of the SiC SBD, is developed. The C-V characteristics are evaluated through experiments over the rated voltage range. These results explain the punch-through structure and device parameters. The dynamic behavior of the proposed model is validated through experiments on half-wave rectification of ac voltages over a wide frequency range. As a relational expression of voltage, current, and frequency of an applied ac sinusoidal voltage, the performance criterion of the device is established for rectification. The model also quantitatively assesses the switching capability of SiC SBDs. The model and performance criteria are beneficial for circuit design and device evaluation.

Photoluminescence and electroluminescence from Eu-activated CaAl2O4-based multicomponent oxide thin-film phosphors

Photoluminescence (PL) and electroluminescence (EL) from newly developed Eu-activated CaAl2O4 -based multicomponent oxide phosphor thin films prepared by rf magnetron sputtering are described. Yellowish green and blue emissions in PL were obtained in as-deposited and postannealed ((CaAl2O4)1−x–(BaAl2O4)x):Eu and ((CaAl2O4)1−x–(MgAl2O4)x):Eu thin films, respectively. In addition, blue emission in EL was observed from thin-film electroluminescent (TFEL) devices fabricated by using ((CaAl2O4)1−x–(BaAl2O4)x):Eu thin films postannealed at 1000°C in an Ar+H2(5%) gas atmosphere. A luminance of 3.2cd∕m2 for blue emission was obtained in a ((CaAl2O4)0.44–(BaAl2O4)0.56):Eu TFEL device driven by a 1kHz sinusoidal wave ac voltage; the blue EL emission corresponds to the CIE color coordinates of (x=0.24, y=0.13).

Optoelectronic Characteristics of Direct-Current and Alternating-Current White Thin-Film Light-Emitting Diodes Based on Hydrogenated Amorphous Silicon Nitride Film

Direct-current and alternating-current white thin- film light-emitting diodes (DCW and ACW TFLEDs) have been fabricated and demonstrated with the intrinsic hydrogenated amorphous silicon nitride (i-a-SiN:H) film as the luminescent layer. The achievable brightness of the representative DCW and ACW TFLEDs were 200 and 170 cd/m2 at an injection-current density of 600 and 100 mA/cm2, respectively. The electroluminescence (EL) threshold voltage of the DCW TFLED was 10.9 V, and its peak wavelength and full-width at half-maximum (FWHM) of the EL spectrum were about 455 and 230 nm, respectively. For the ACW TFLED, the EL threshold voltage was 8.4 V, and its peak wavelength and FWHM of the EL spectrum were about 535 and 260 nm, respectively. In addition, their current-conduction mechanism was also investigated. Within the lower applied-voltage region, they showed an ohmic current, while for the higher applied-voltage region, the Frenkel-Poole emission was the main mechanism. It was also found that the H2 -plasma treatment of luminescent i-a-SiN:H layer of an ACW TFLED played an important role in improving device performances, such as decreased EL threshold voltage, increased brightness, and broadened and blue-shifted EL spectrum. The EL spectra of an ACW TFLED under either DC forward or reverse bias or the sinusoidal AC voltage were qualitatively very similar, with a peak wavelength at about 535 nm and a broad FWHM about 260 nm. Moreover, the EL intensity of an ACW TFLED increased with an AC frequency of up to 180 kHz and, then, decreased rapidly and became very weak as the frequency was up to about 500 kHz.

SNS Josephson Junction Series Arrays for the Josephson Arbitrary Waveform Synthesizer

The Josephson arbitrary waveform synthesizer (JAWS) allows AC voltages to be generated with fundamental accuracy. Lumped arrays of superconductor/normal conductor/superconductor (SNS) Josephson junctions were developed and investigated for this application. Combining electron-beam lithography and chemical-mechanical polishing, series arrays of sub-micrometer SNS junctions consisting of Nb/HfTi/Nb were fabricated. The junction size varied from 0.04 mum2 to 4 mum2 in series arrays up to 2560 junctions in different microwave designs. Stable Shapiro steps are generated in a frequency range from 5 GHz to 20 GHz using continuous microwave irradiation. Using a simple pulse pattern at different pulse repetition frequencies, the arrays show current-voltage characteristics with flat Shapiro steps. Sinusoidal AC voltages were synthesized using a commercial pulse pattern generator. Peak-to-zero voltages of some mV for frequencies below 1 kHz were achieved. Higher harmonics were measured to be more than 80 dB below the fundamental tone. The behavior of the arrays was investigated in more detail by measuring the amplitude-frequency spectra.

Hydrogenated Amorphous Silicon Carbide Alternating-Current Thin-Film Light-Emitting Diodes

Hydrogenated amorphous silicon carbide alternating-current thin-film light-emitting diodes ( ACTFLEDs) have been successfully fabricated on indium-tin-oxide-coated glass substrates and characterized. The electroluminescence (EL) spectra of an obtained ACTFLED under either a dc (positive or negative) bias or a sinusoidal ac voltage were qualitatively very similar, with a peak wavelength at about and a shoulder at about . The EL threshold voltage and brightness of the ACTFLEDs were sensitive to the contact behavior between the metal electrode employed and amorphous film. Moreover, the EL intensity of an ACTFLED increased with the frequency up to and then decreased rapidly and became very weak as the frequency increased to about . A model based on the equivalent circuit has also been proposed to explain this frequency-dependent EL behavior.

Integrated Low-Loss CMOS Active Rectifier for Wirelessly Powered Devices

A low-loss CMOS full-wave active rectifier is presented. It consists of two dynamically biased and symmetrically matched active diodes each realized by an nMOS switch driven by a 2-ns voltage comparator with reverse-current control. With a load of 1.8-kOmega, the rectified dc voltage is 3.22 V and 1.2 V for a 13.56 MHz ac sinusoidal input voltage of 3.5 V and 1.5 V respectively. It is fabricated in a 0.35-mum CMOS process with an active area of 0.0055 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , with no low-threshold devices and on-chip passive components

The uni-polarity phase-shifted controlled voltage mode AC–AC converters with high frequency AC link

A circuit configuration and circuit topological family of voltage mode ac–ac converters with high frequency ac links, which are based on forward converters, and a uni-polarity phase-shifted control strategy are proposed and deeply investigated. These kinds of converters consist of a input cycloconveter, a high frequency transformer, an output cycloconverter, input and output filters, and can transfer an unsteady ac voltage with a high harmonic into steady same-frequency ac sinusoidal voltage with a low harmonic. By using uni-polarity phase-shifted control strategy, output filtering inductance current is naturally commutated, and zero voltage switching of the output cycloconverter is realized. The converters’ averaging model, the output characteristic curve, and design criteria for the key circuit parameters are given. The theoretical analysis and test result of 1 kVA 220 V ± 10% 50 Hz ac/110 V 50 Hz ac prototype have shown that the converters have such advantages as high frequency electrical isolation, simple topology, two-stage power conversion (LFAC/HFAC/LFAC), bidirectional power flow, uni-polarity synchronized pulsewidth modulation waveform, high efficiency, high power density, high steady precision, low total harmonic distortion of the output voltage, strong adaptability to various loads, high line power factor, and low audio noise etc.

A novel synchronism method for thyristor power converters using the space vector approach

Phase-controlled operation of thyristor power rectifiers requires instantaneous phase information of the fundamental component of the grid voltage in order to generate the proper gating sequence. In many high-power, high-precision applications, such as driving the bending magnets of large particle accelerators, the power converters are fed from a local grid, which produces significant frequency variations and large voltage notches superimposed to the sinusoidal AC voltage due to the commutation interval. These strong disturbances impose some difficulties in measuring the phase of the mains, affecting the precision of the converter. In this paper, we present a new method to generate a fast and precise synchronism signal based on the concept of space vectors. The proposed method allows to track line frequency changes within one cycle of the mains in spite of the large voltage notches produced by the commutation overlap angle. Simulation and experimental results are provided.

Ultraviolet emission intensity, visible luminance, and electrical characteristics of small arrays of Al∕Al2O3 microcavity plasma devices operating in Ar∕N2 or Ne at high-power loadings

Small arrays (3×3→10×10) of microcavity plasma devices, having a two-stage structure comprising multilayer stacks of nanostructured Al2O3 grown on Al foil with cylindrical microcavities 100–300μm in diameter, produce intense ultraviolet (UV) and visible emission when operated in Ar∕3% N2 gas mixtures or Ne and excited by a sinusoidal ac voltage wave form. Near-UV (300–400nm) intensities emitted into a solid angle of ∼10−2sr above 30 mW per cm2 of radiating area are measured for Ar∕N2 gas mixture pressures of 400–800Torr, an excitation frequency of 15kHz, and an average current ⩾20mA (rms). Two or more conjoined cylindrical microcavities of differing diameters allow for the confinement of the plasma to progressively smaller volumes as the power deposited is increased (thereby decreasing the Debye length and the spatial extent of the cathode fall region) and provides a convenient tool with which the luminosity of an array can be modulated. The transition of a microplasma from confinement in a 200-μm-diam cavity into an adjacent 100-μm-diam microcavity is accompanied by an order-of-magnitude increase in the luminance of Ne plasmas in a 3×3 array as the rms current is increased by ∼1mA.

Design of Electrical Mathematics for Improvement of Skill in Electric Circuits and Electromagnetic

Design of electrical mathematics and evaluating results of the course are described in this paper. The design was carried out based on the analysis using questionnaires done to the third grade students in Iwate University. One of the analysis results with the questionnaires, many student feel the difficulty to understand in treatment of sinusoidal ac current and voltage with employment of complex numbers. Based on the analysis, the content of electrical mathematics was designed with focusing easy to use the mathematical technique to solve problems in electrical circuit and/or electromagnetic. The designed electrical mathematics was carried out in Iwate University and was evaluated by tests and questionnaires. The results showed the designed electrical mathematics contributed toward well-understanding the electrical circuits and/or the electromagnetics for students.

Large Arrays of Microcavity Plasma Devices for Active Displays and Backlighting

Developments of the past several years in the technology of microcavity plasma devices having characteristic dimensions of 10-100 /spl mu/m suggests their applicability to the next generation of active and passive displays. Two examples of device structures that are well suited for economically manufactured arrays of large active area are presented. Arrays as large as 500/spl times/500 (2.5/spl middot/10/sup 5/) pixels of Si inverted pyramid microplasma devices, with emitting apertures of 50/spl times/50 /spl mu/m/sup 2/ and designed for AC or bipolar excitation, have been designed and operated successfully in the rare gases at pressures up to and beyond one atmosphere. Multilayer Al/nanostructured Al/sub 2/O/sub 3/ microplasma devices having 100-300 /spl mu/m diam. cylindrical microcavities are robust and operate in the abnormal glow mode for rare gas or Ar/2-5% N/sub 2/ mixture pressures of 500-700 torr. Grown by a wet chemical process, the nanoporous Al/sub 2/O/sub 3/ dielectric yields a lightweight, flexible structure that produces intense visible or ultraviolet emission when driven by sinusoidal AC or bipolar voltage waveforms.