Dc Operation Mode Research Articles

Isolated High-Frequency Link PFC Rectifier With High Step-Down Factor and Reduced Energy Circulation

This article presents an isolated single-stage ac–dc high-frequency link full-bridge cycloconverter (HFLC) with high conversion ratio. Despite certain advantages, such topologies generally suffer from transformer leakage inductance problems and lack of effective modulation methods, particularly in the ac–dc operation mode. In this study, for the input current regulation with the power factor correction of the HFLC, a novel phase-shift modulation method is used. It allows soft-switched turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> of the dc-side transistors and zero current switching of the ac-side matrix switches without additional circuits or topology modifications. The introduced time-varying regulation of the peak current can be easily implemented; as a result, merely minor energy circulation occurs. Moreover, two of the ac-side transistors operate with fundamental frequency. Design constraints of the concept are analyzed and discussed. For verification, a 1.2-kW 230 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AC</sub> to 48 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> experimental prototype is used.

Разработка масштабируемой малосигнальной модели 0,1 мкм GaAs-pHEMT-транзистора для усилительных применений

This work deals with the development of a 0.1-µm GaAspHEMT-model for use in EDA applications. The model is constructed using a reference transistor with a total gate width of 635 μm, which showed good accuracy under different DC operation modes in a wide frequency range. The developed model can be used to speed up and reduce the cost of the monolithic microwave integrated circuit amplifiers design in which the pHEMT transistor is the basic active element. In further studies the obtained model will be extended to develop more complex types of models, such as noise and nonlinear ones.

Comparison of thermal properties of a hot target magnetron operated in DC and long HIPIMS modes

Thermal properties of the magnetron discharge with uncooled copper and chromium targets were studied experimentally and theoretically for DC and long HiPIMS (L-HiPIMS) operation modes. A set of thermal fluxes was considered to build a numerical model of the hot target exposed to DC and high-power pulsed plasma. The modeling results were tested in the experiments. The temperature of targets was measured directly in course of magnetron discharge operation with an elaborated contact thermocouple method. The measurements were made in two modes. At first the temporal evolution of temperature was recorded for a fixed applied discharge power. The results were found to well agree with temperature values expected from calculations. At 2 kW power, it takes ~50 s to reach the melting point of copper. The steady-state temperature values were also measured for a number of discharge power levels. The obtained dependence clearly demonstrated that the main mechanisms of the target heat balance at high temperatures are surface radiation and heat transfer due to thermal conductivity of the heat insulation supports between the target and water-cooled cathode. The parameters of DC hot target magnetron were compared to the high-power pulsed regime with the pulse-on time 20 ms. A promising method of a hot target magnetron discharge operation was considered that involves applying long (>20 ms) high-power pulses to the target pre-heated in the DC mode during the pulse-off period.

Numerical analysis of thermo-electric field for AC XLPE cables with different service times in DC operation based on conduction current measurement

This paper presents an estimate for the influence of service time on the conduction current characteristics of a 10 kV AC XLPE. The experimental conduction current results show that the space charge accumulation threshold increases with service time. Fourier transform infrared (FT-IR) and differential scanning calorimetry (DSC) experiments show increased thermo-oxidative aging and reduced crystallinity as the service time increases. This results in deeper traps in the XLPE material which can be verified from isothermal surface potential decay experiments. Based on the experimental results, the numerical analysis of thermo-electric fields is carried out for 10 kV AC XLPE cables with different service times under bipolar DC operation mode. It shows that the DC power for 10 kV AC XLPE cable in bipolar DC operation is higher than the AC power, whereas the DC operating voltage and DC power increases with the service time. In order to ensure a safe and long service life of the cables in DC operation, a conductor temperature of 60 °C and DC operating voltage of 11 kV are recommended for 10 kV AC XLPE cables in bipolar DC operation.

Coordination control for multi-voltage-level dc grid based on the dc–dc converters

Dc–dc converters are emerging as a key device for future dc transmission networks. This paper develops a switch mode control and a dc–dc coordination control for dc–dc converters’ coordinated operation in the multi-voltage-level dc grid. The switch mode control is a local controller on the dc–dc converter to enable the automatic switch of the dc–dc operation mode. The dc–dc coordination control is an advanced control based on the switch mode control. With the dc–dc coordination control, unbalanced power from one dc grid could be optimally distributed to other grids, in order to avoid serious power fluctuation events. Simulation results are provided to demonstrate the performance of the switch mode control and dc–dc coordination control.

Comparison of SNSPDs Biased With Microwave and Direct Currents

This paper presents a detailed investigation of superconducting nanowire single-photon detectors (SNSPDs) biased with microwave and direct currents. We developed a hybrid detector, which allows the operation in the rf and dc operation mode. With this hybrid detector, we are able to compare the count rates of the same nanowire biased with dc and rf currents. Furthermore, we demonstrate the use of the oscillating current in the rf operation mode as a reference signal in a synchronous single-photon detection mode.

Thermo‐electric field analysis of AC XLPE cable in monopole, bipole, and tripole DC operation modes

This paper presents a numerical analysis of thermo-electric fields of 10 and 35 kV AC XLPE cables in monopole, and tripole DC operating modes based on conduction current measurements. DC conductivities and electric field thresholds of the space charge accumulation for XLPE materials were estimated at different temperatures and electric fields. The result showed that the electric field threshold of the space charge accumulation for the materials reduced with an increase of the temperature. DC currents of the cables were increased with the increase of the operating temperatures in the three DC operation modes. The maximum DC operation voltage of the cables increased with the decline of the operation temperature in the three DC operation modes. The maximum transient electric fields were below the threshold of the space charge accumulation for the cables in the tripole DC operation. The maximum transmission power of the 10 kV XLPE cable in the DC operation modes was at 60°C, whereas the maximum transmission power of the 35 kV XLPE cable was at 50°C. It was elucidated that the 10 kV AC XLPE cable could have more advantages than the 35 kV AC XLPE cable in the three DC operation modes.

Investigation of Short-Arc High-Pressure Xenon Discharge: Effect of Electrode Material Evaporation on Discharge Properties and Pulse Operation

This paper presents and discusses the experimental data obtained in the investigation of a short-arc high-pressure xenon discharge in dc and pulse-periodic operation modes. In the case of the dc discharge, the main focus of attention is the cathode material (thorium) evaporation into the plasma. Spectroscopic measurements show that this process strongly influences the plasma characteristics and first of all the plasma optical emission. Due to low ionization energy, thorium atoms decrease the plasma temperature at the cathode, which is confirmed by experimentally obtained spectra with an unexpectedly low optical emission temperature. The fact cannot be interpreted without the assumption of cathode material evaporation: in a homogeneous short-arc gas discharge with a conical cathode, the emission temperature at the cathode should not be low because the strength of the electric field is obviously maximal near the cathode tip. The findings are important for modeling discharges of such kind. For the pulse-periodic discharge, two effects are described: a decrease in the anode temperature and an increase in the light efficiency of about 35% in some discharge conditions. These can be used for the development of more powerful and effective xenon light sources.

A Superconducting Vernier Motor for Electric Ship Propulsion

A megawatts (MW)-class direct-drive vernier motor for electric ship propulsion is proposed in this paper. The proposed vernier motor adopts the homopolar structure and utilizes the high-temperature superconducting wire for electrical excitation. The stator houses the superconducting field winding and the copper armature winding. The rotor consists of an iron core without excitation sources. Thus, no cryo-moving components are required. A dual-body Dewar for cooling the pancake high-temperature superconducting field winding is proposed. The motor performance is analyzed and evaluated using three-dimensional finite-element analysis. Both the brushless ac and brushless dc operation modes for the proposed motor are assessed and compared.

Supercapacitors: Solid-State Dual Function Electrochemical Devices: Energy Storage and Light-Emitting Applications (Adv. Energy Mater. 19/2016)

In article number 1600651, Keun Hyung Lee, Jong-Lam Lee, and co-workers describe a switchable dual-function electronic device that can store electric charges and emit photons with λ = 620 nm using ionic liquid based polymer gel electrolytes, ion gels. A sandwich-type device performs energy storage function through pseudo-capacitive charge transfer reactions in a DC operation mode and the same device radiates light through electrochemiluminescent redox reactions under an AC condition.

A Physics-Based Compact Model of Metal-Oxide-Based RRAM DC and AC Operations

A physics-based compact model of metal-oxide-based resistive-switching random access memory (RRAM) cell under dc and ac operation modes is presented. In this model, the conductive filament evolution corresponding to the resistive switching process is modeled by considering the transport behaviors of oxygen vacancies and oxygen ions together with the temperature effect. Both the metallic-like and electron hopping conduction transports are considered to model the conduction of RRAM. The model can reproduce both the typical I-V characteristics of RRAM in high-/low-resistance state (LRS) and the nonlinear characteristics in LRS. Moreover, to accurately model ac operation mode, the effects of parasitic capacitance and resistance are included in our model. The developed compact model is verified and calibrated by measured data in different HfOx-based RRAM devices under dc and ac operation modes. The excellent agreement between the model predictions and experimental results shows a promising prospect of the future implementation of this compact model in large-scale circuit simulation to optimize the design of RRAM.

Quantitative scanning thermal microscopy based on determination of thermal probe dynamic resistance

Resistive thermal probes used in scanning thermal microscopy provide high spatial resolution of measurement accompanied with high sensitivity to temperature changes. At the same time their sensitivity to variations of thermal conductivity of a sample is relatively low. In typical dc operation mode the static resistance of the thermal probe is measured. It is shown both analytically and experimentally that the sensitivity of measurement can be improved by a factor of three by measuring the dynamic resistance of a dc biased probe superimposed with small ac current. The dynamic resistance can be treated as a complex value. Its amplitude represents the slope of the static voltage-current U-I characteristic for a given I while its phase describes the delay between the measured ac voltage and applied ac current component in the probe. The phase signal also reveals dependence on the sample thermal conductivity. Signal changes are relatively small but very repeatable. In contrast, the difference between dynamic and static resistance has higher sensitivity (the same maximum value as that of the 2nd and 3rd harmonics), and also much higher amplitude than higher harmonics. The proposed dc + ac excitation scheme combines the benefits of dc excitation (mechanical stability of probe-sample contact, average temperature control) with those of ac excitation (base-line stability, rejection of ambient temperature influence, high sensitivity, lock-in signal processing), when the experimental conditions prohibit large ac excitation.

On Self-Organized Criticality of the East China AC–DC Power System—The Role of DC Transmission

In this paper, we aim to analyze the impact of dc transmission on self-organized criticality (SOC) of the East China power system (ECPS), which is a large-scale, ac-dc interconnected and classical receiving-end power system. To this end, a detailed ac-dc cascading failure analysis model is established to study the SOC of this system. In the proposed model, some important issues of dc transmission and several kinds of stochastic factors are considered. The corresponding algorithm realized on the platform of the PSS/E software is discussed as well. Simulation based on the 2010 East China ac-dc power system is performed and the following results are obtained: 1) the dc issues such as the operation modes and the control parameters have obvious effects on the SOC of the ac-dc system and 2) the risk of cascading failure and blackout can be decreased by deliberately choosing the dc operation modes and control parameters.

Note: High precision angle generator using multiple ultrasonic motors and a self-calibratable encoder

We present an angle generator with high resolution and accuracy, which uses multiple ultrasonic motors and a self-calibratable encoder. A cylindrical air bearing guides a rotational motion, and the ultrasonic motors achieve high resolution over the full circle range with a simple configuration. The self-calibratable encoder can compensate the scale error of a divided circle (signal period: 20") effectively by applying the equal-division-averaged method. The angle generator configures a position feedback control loop using the readout of the encoder. By combining the ac and dc operation mode, the angle generator produced stepwise angular motion with 0.005" resolution. We also evaluated the performance of the angle generator using a precision angle encoder and an autocollimator. The expanded uncertainty (k = 2) in the angle generation was estimated less than 0.03", which included the calibrated scale error and the nonlinearity error.

Overview of Stator-Permanent Magnet Brushless Machines

Permanent magnet (PM) brushless machines having magnets and windings in stator (the so-called stator-PM machines) have attracted more and more attention in the past decade due to its definite advantages of robust structure, high power density, high efficiency, etc. In this paper, an overview of the stator-PM machine is presented, with particular emphasis on concepts, operation principles, machine topologies, electromagnetic performance, and control strategies. Both brushless ac and dc operation modes are described. The key features of the machines, including the merits and drawbacks of the machines, are summarized. Moreover, the latest development of the machines is also discussed.

Intrinsic noise variation in an amplifier based on a heterojunction bipolar transistor amplifier in nonlinear mode

Intrinsic noise variation in a heterojunction bipolar transistor amplifier with intense interference at its input was analyzed using the Volterra series method. During the analysis, the nonlinearity of correlated sources of collector and base noise currents was considered. It was shown that the change in noise at the amplifier output caused by interference depends on both nonlinear properties of the transistor and its dc operation mode, as well as the ratio of the levels of all its intrinsic noise sources.

Pulsed-DC selfsputtering of copper

At standard magnetron sputtering conditions (argon pressure ~0.5 Pa) inert gas particles are often entrapped in the formed films. Inert gas contamination can be eliminated by using the self-sustained magnetron sputtering process because it is done in the absence of the inert gas atmosphere. The self-sustained sputtering (SSS) gives also a unique condition during the transport of sputtered particles to the substrate. It is especially useful for filling high aspect ratio submicron scale structures for microelectronics. So far it has been shown that the self-sputtering process can be sustained in the DC operation mode (DC-SSS) only. The main disadvantage of DC-SSS process is instability related to possible arc formation. Usage of pulsed sputtering, similarly to reactive pulsed magnetron sputtering, could eliminate this problem. In this paper results of pulsed-DC self-sustained magnetron sputtering (pulsed DC-SSS) of copper are presented for the first time. The planar magnetron equipped with a 50 mm in diameter and 6 mm thick copper target was powered by DC-power supply modulated by power switch. The maximum target power was about 11 kW (~550W/cm2). The magnetron operation was investigated as a function of pulsing frequency (20–100 kHz) and duty factor (50–90%). The discharge extinction pressure was determined for these conditions. The plasma emission spectra (400–410nm range) and deposition rates were observed for both DC and pulsed DC sustained self-sputtering processes. The presented results illustrate that stable pulsed DC-SSS process can be obtained at pulsing frequency in the range of 60–100 kHz and duty factor of 70–90%.

High-performance permanent magnet brushless motors with balanced concentrated windings and similar slot and pole numbers

The paper presents a comparison between the performances of exterior-rotor permanent magnet brushless motors with distributed windings and the performances of exterior-rotor permanent magnet brushless motors with concentrated windings. Finite element method analysis is employed to determine the performance of each motor. It is shown that motors with concentrated windings and similar slot and pole numbers exhibit similar or better performances than motors with distributed windings for brushless AC (BLAC) operation mode and brushless DC (BLDC) operation mode as well.

A simple large signal model for III–V HBT devices exceeding VBIC performances

This paper presents a large signal compact circuit simulation model for III–V heterojunction bipolar transistors (HBTs). The model is implemented as a user compiled model (UCM), in the agilent ADS circuit simulator, using C code. Though its simplicity, the model includes all physical effects taking place in power III–V-based HBT devices. It is verified by comparing its simulations to measurements in DC, small-signal and large-signal operation modes. The proposed model is further tested by comparing it to the established VBIC model and the newly introduced Agilent HBT model. It is found that despite its reduced complexity, the proposed model gives better agreement with measurements than the VBIC model in all modes of operation.

Collection efficiency of ultrafine particles by an electrostatic precipitator under DC and pulse operating modes

High particle collection efficiency in terms of particle weight volume mg/m/sup 3/ is well achieved by a conventional electrostatic precipitator (ESP). However, the collection efficiencies in terms of number density for the ultrafine (particle size between 0.01 to 0.1 /spl mu/m) or submicron particles by a conventional ESP are still relatively low. Therefore, it is necessary to improve the collection efficiency for ultrafine particles. In this work, attempts have been made to improve the ultrafine particle collection efficiency using the short pulse energizations. The present version of ESP consists of three sets of wire plate type electrodes. For ESP under DC operation modes, experimental results show that the collection efficiency for DC applied voltage decreases with increasing dust loading when particle density is larger than 2.5/spl times/10/sup 10/ part/m/sup 3/. For ESP under pulse operating modes, the particle collection efficiency increases with increasing pulse peak voltage until 25 kV then decreases with increasing pulse peak voltage. The ultrafine particle collection efficiency based on particle density by DC energizations is much higher compared with pulse energizations without DC bias may be due to the reentrainments of ultrafine particles.