DC Charging Research Articles

Improved Current and Charge Amplifiers for Driving Piezoelectric Loads, and Issues in Signal Processing Design for Synthesis of Shunt Damping Circuits

Piezoelectric transducers are known to exhibit less hysterisis when driven with current or charge rather than voltage. Despite this advantage, such methods have found little practical application due to the poor low-frequency response of present current and charge driver designs. This paper introduces the compliance feedback current driver containing a secondary voltage feedback loop to prevent DC charging of capacitive loads and to compensate for any voltage or current offsets within the circuit. Low-frequency bandwidths in the milli-Hertz range can be achieved. One application for such a device is the synthesis of piezoelectric shunt damping circuits. A number of block diagram transformations are presented to simplify the realization of analog or digital admittance transfer functions from aschematic circuit diagram.

Monitoring state-of-charge of Ni–MH and Ni–Cd batteries using impedance spectroscopy

This paper reports on laboratory studies into the ac impedance spectra of nickel–metal hydride and nickel–cadmium batteries, aiming at finding out possible correlation between electrical parameters, extracted directly from the high frequency region, and the battery state-of-charge (SoC). Impedance diagrams were recorded immediately after interrupting the dc charge, or discharge, current. The study revealed that the series resonance frequency, at which the dynamic cell behavior switches from an inductive character (Z″>0) to a capacitive one (Z″<0), varied monotonously as a function of state-of-charge. This behavior was reproducible after intermittent charge and discharge. Half-cell measurements were also conducted to associate the cell impedance with either processes occurring at the positive or negative plates.

Precision current and charge amplifiers for driving highly capacitive piezoelectric loads

Piezoelectric transducers are known to be highly capacitive loads that exhibit less hysterisis when driven with current or charge rather than voltage. Compliance feedback current and charge amplifiers are introduced. A secondary output voltage feedback loop is employed to prevent DC charging of capacitive loads and to compensate for any voltage or current offsets in the driver circuit. Low frequency bandwidths in the milliHertz range can be achieved.

Characterization of a high-intensity unipolar-mode pulsed ion source with improved magnetically insulated diode

A magnetically insulated ion diode (MID) with an improved external-magnetic field system has been developed and installed onto a TEMP-6-type high-intensity pulsed ion source in order to produce a high-intensity pulsed ion beam (HIPIB) for surface modification of materials. The external-magnetic field MID is operated in unipolar mode based on dielectric high-voltage flashover, and a double coaxial pulse-forming line (PFL) powered with a Marx generator is used to form the unipolar pulse of nanosecond width. A specially designed cathode has been constructed with a forked connection to two symmetrically installed transformers to improve the effect of the magnetic field and thus increase the stability of generation and propagation of the ion beam. It was found that the efficient generation of HIPIB mainly depended on the magnetic field strength, the gas pressures in reverse and output switches of PFL, and the anode–cathode (A–K) gap of the external-magnetic field MID. A proper magnetic field strength was found with magnetic field power system at dc charging voltage of 8 kV. The proper A–K gap distance is not uniform with the value varied from 6 to 8 mm. Suitable gas pressures for reverse and output switches were about 1.2 and 2.4 atm, respectively, at a charging voltage of 40 kV to the Marx generator. The most efficient plasma generation and ion extraction led to a maximum output of HIPIB with a peak ion current density of 300 A cm−2 and a beam pulse width of 80 ns (full width at half maximum), at an accelerating pulse of 300–350 kV with a pulse width of 70 ns.

Performance of gas-puffing inverse pinch switch for pulsed power system

The design technology of a closing switch, especially inverse pinch switch (IPS) triggered by N/sub 2/ gas for a high voltage and current is described in this paper. Also, the capacitor banks, control system, dc charging system, and high-current cable system, etc., are introduced. In contrast to a conventional trigatron switch in which the current is constricted by a z-pinch mechanism, the new switch operates in an inverse-pinch geometry formed by a metal chamber, greatly reducing hot-spot formations on the electrode surfaces. A prototype of the IPS with a N/sub 2/ gas-puffing trigger was fabricated for breaking a large current up to 250 kA. The geometry of the IPS not only eliminates the z-pinch effects, but utilizes J/spl times/B=F force for reducing the current density. Force acting on the plasma is directed radially outward in the IPS. The annular current path is radially dispersed, which results in a low current density, running-arc mode, and a low inductance. It was shown that in comparison with the spark gap, the switch inductance and current density of the IPS are largely reduced and the useful lifetime is significantly increased. The IPS enabled the closing of very high voltage and current.

Floquet scattering theory of quantum pumps

We develop the Floquet scattering theory for quantum mechanical pumping in mesoscopic conductors. The nonequilibrium distribution function, the dc charge and heat currents are investigated at arbitrary pumping amplitude and frequency. For mesoscopic samples with discrete spectrum we predict a sign reversal of the pumped current when the pump frequency is equal to the level spacing in the sample. This effect allows to measure the phase of the transmission coefficient through the mesoscopic sample. We discuss the necessary symmetry conditions (both spatial and temporal) for pumping.

All solid electric double layer capacitors based on Nafion ionomer

The aim of the present work is to demonstrate that an efficient all solid electric double layer capacitor (EDLC) may be realised with electrolyte membrane and carbon based electrodes prepared by using a Nafion ionomer solution. Polymer membrane was prepared by a casting method. Electrodes were prepared with two overlapped layers formed of a carbon–Nafion layer and a carbon paper substrate. Three different electrolyte separators in capacitor configuration have been tested and compared: (1) a commercial Nafion 115 membrane (N115), (2) a membrane prepared by casting the Nafion 1100 solution (NRG50) and (3) a porous glass fibre matrix impregnated with a 1 M H 2SO 4 solution (FVH2SO4). The membrane and electrodes assemblies (MEA) had thickness of 0.6–0.8 mm and geometric area of 4 cm 2. The EDLCs characteristics have been studied by conductivity, cyclic voltammetry and DC charge–discharge methods. Proton conductivities of 5.7×10 −2 and 3.1×10 −2 S cm −1 have been measured at room temperature for the N115 and the NRG50, respectively. Specific capacity of 13.2 F g −1 has been obtained by capacitor utilising the cast Nafion membrane. This value is 70% of specific capacity obtained from the capacitor using sulphuric acid and about 140% of that using Nafion 115.

Tantalum oxide–ruthenium oxide hybrid (R) capacitors

A hybrid capacitor consisting of porous tantalum oxide anode electrode and ruthenium oxide cathode electrode was examined and characterized. The capacitor has a capacitance of 35 mF and an internal resistance of 45 mΩ. It was found that the capacitance was insensitive to current density up to 110 mA/cm 2, and temperature ranging from −70 to 50 °C. During dc charge and discharge cycles, the potential of the cathode electrode was within the electrochemical stability window. However, a sudden voltage-jump as high as 7.5 V could occur at the cathode electrode during a short circuit discharge. A simple model was established to describe the transient behavior of cathode and anode electrodes. It was found that the voltage-jump was proportional to the ratio of the internal resistance of the cathode electrode to the total resistance of the capacitor. The resistance distribution inside the capacitor was also determined to be 47, 28, and 25% from the cathode, anode, and electrolyte, respectively.

A dc charge sheet turn-on model for the I–V characteristics of doped polysilicon thin film transistors

An explicit semi-empirical analytical model for surface potential is proposed for doped polysilicon thin film transistors (poly-Si TFTs). The model shows good agreement with numerical calculation of surface potential in the weak and strong inversion regions. Further, a surface-potential-based dc charge sheet turn-on model is also proposed for small grain doped poly-Si TFTs. The validity of the model is tested by using measured ID–VDS and ID–VGS data for n-channel doped poly-Si TFTs. The results show that the drain current in the device is predicted by the model with good accuracy. Although the model does not consider the grain boundary potential barrier ΨB explicitly, the validity of the model is attributed to the fact that in the turn-on region the gate voltage is sufficiently high resulting in a decrease of ΨB to low values and thus not affecting the drain current significantly. The model also considers the kink effect which becomes dominant at higher drain to source voltage.

Characterization of a high-intensity bipolar-mode pulsed ion source for surface modification of materials

A high-intensity pulsed ion source of TEMP-type series, operating in bipolar mode, has been developed as a unique pulsed energy source to produce a high-intensity pulsed ion beam (HIPIB) for surface modification of materials. To generate the ion beam, a specially shaped bipolar pulse, consisting of a first negative pulse and a second delayed positive pulse both of nanosecond width, is formed by a double coaxial pulse-forming line (PFL) powered with a Marx generator and supplied to a magnetically insulated ion diode (MID) by a self-magnetic field. It is found that the efficient generation of a HIPIB is mainly dependent on the delay time of the bipolar pulse, adjusted by pressure ratio in the two gas switches of a PFL, and the anode–cathode (A–K) gap distance in the self-magnetic field MID. The delay time determines the effective area on the anode surface for plasma generation and the A–K gap distance ensures the stability of the process. A proper delay time and a proper A–K gap distance are obtained by a series of experimental investigations. Under delay time from 30 to 280 ns and several different A–K gap distances, the typical wave forms of the bipolar pulses at a dc charging voltage of 45 kV to Marx generator are illustrated to clarify the effects of delay time and A–K gap distance on the ion beam generation. The proper A–K gap distance is not uniform, varied from 6 to 8 mm, and the corresponding proper delay time is 250 ns. The most efficient plasma generation leads to a maximum output of HIPIB with a peak ion current density of 350 A cm−2 and a beam pulse width of 75 ns (full width at half maximum), at an accelerating pulse of 220 kV with a pulse width of 100 ns.

The effects of pulse charging on cycling characteristics of commercial lithium-ion batteries

The effects of a pulse charging technique on charge–discharge behavior and cycling characteristics of commercial lithium-ion batteries were investigated by comparison with the conventional direct current (dc) charging. The impedance spectra and cycling voltammograms of Li-ion batteries cycled by both protocols have been measured. The individual electrodes in the batteries have also been examined using XRD and SEM. The results show that pulse charging is helpful in eliminating concentration polarization, increasing the power transfer rate, and lowering charge time by removing the need for constant voltage charging in the conventional protocol. Pulse charging interrupts dc charging with short relaxation periods and short discharge pulses during charging, and also improves the active material utilization giving the battery higher discharge capacity and longer cycle life. Impedance measurements show that the magnitude of the interfacial resistance of the batteries cycled both by pulse charging and dc charging is small. However, at the same number of cycles, the interfacial resistance of the pulse charged battery is larger than that of dc charged. The batteries after 300 cycles charged by pulse charging show higher peak currents during both forward and reverse scans indicating higher reversibility of the electrodes. XRD and SEM studies of the individual electrodes indicate that pulse charging maintains the stability of the LiCoO 2 cathode better than dc charging and inhibits the increase in the thickness of the passive film on the anode during cycling.

Analysis of power limitations at porous supercapacitor electrodes under cyclic voltammetry modulation and dc charge

A simple capacitor is perceived as being capable of discharge (or recharge) at high rates, limited only by a small equivalent series resistance. However, in the case of electrochemical capacitors, based on high specific area porous electrode materials, power limitations arise due to the complex-distribution of electrolyte internal resistance, coupled with double-layer or pseudo-capacitative elements. The present paper quantitatively examines both numerically and experimentally the effects of internal electrolyte resistance as evaluated by the current-response functions for porous capacitor electrodes, generated in cyclic voltammetry (CV) experiments and for voltage versus time responses in dc charge/discharge regimes.

Empirical Model of Flicker in Silicon Light Valves

We have performed systematic characterizations of flicker in silicon light valves. It was found that temperature was the most important factor associated with flicker. Temperature could assist conduction mechanisms in silicon light valves and enhance the flicker accordingly. The major conduction mechanisms of flicker in silicon light valves were residual DC charge on the silicon surface, the voltage holding capability of a liquid crystal cell, the voltage holding capability of a silicon panel, light leakage and parasitic capacitor coupling. Major causes of these flicker mechanisms were identified through systematic characterizations. An empirical model of flicker was proposed with quantitative experimental data and theories. Among these conduction mechanisms, temperature could boost the voltage holding capabilities of a silicon panel to become the most dominant cause of flicker when the temperature was above 40°C. At temperatures below 30°C, the other four conduction mechanisms contributed to the flicker in different ways. Minimization of flicker could be achieved through materials and device optimization.

Surface-potential-based charge sheet model for the polysilicon thin film transistors without considering kink effect

An expression for surface potential for Poly-Silicon Thin Film Transistors (Poly-Si TFT) is derived. The surface potential thus calculated numerically as a function of terminal voltage is used in the proposed dc charge sheet model for Poly-Si TFT to determine the drain current as a of function terminal voltage in the linear and saturation regions using single expression. The model is verified using available experimental data for output and transfer characteristics for different Poly-Si TFTs and shows good agreement with the experimental data. However, the proposed model does not consider the kink effect which is dominant at higher drain to source voltage.

Characterization and minimization of flicker in silicon light valves

We have performed systematic characterizations of flicker in silicon light valves. It was found that there were four conduction mechanisms accounting for the flicker. These four mechanisms were residual dc charge on the silicon surface, voltage holding capability of the liquid crystal cell, voltage holding capability of the silicon panel, and parasitic capacitor coupling of the pixel. Major causes of these four mechanisms were identified. Solutions of flicker minimization were obtained for each mechanism. Among these solutions, offset of common voltage was found very useful to compensate for residual dc charge and parasitic capacitor coupling. Frame rate multiplication was found very useful for the minimization of flicker due to low voltage holding capabilities of the liquid crystal cell and silicon panel.

A three-dimensional multifrequency large signal model for helix traveling wave tubes

A three-dimensional (3D) multifrequency large signal model of the beam wave interaction in a helix TWT is described. The beam is divided into a set of discrete rays, or beamlets, instead of the disks or rings used in one-dimensional (1-D) or two-dimensional (2-D) models. The RF fields supported by the helix are represented by a tape helix model that uses a modal expansion including the full (Bessel function) radial dependence of the fields; both forward and backward synchronous space harmonics are included in the model. RF space charge fields are obtained from solutions of the Helmholtz equations for the RF electric and RF magnetic fields, using the beam current and charge densities as sources. The dc space charge electric field is similarly obtained from a solution of Poisson's equation. This model has been implemented in a code called CHRISTINE 3D, a generalization of the one dimensional CHRISTINE code. The full three dimensional treatment permits the accurate computation of large signal gain and efficiency, taking into account the self-consistent variation of beam radius along the interaction space. The code also computes helix interception current and transverse beam distributions at the entrance to the collector-important design data that are unavailable from a 1D model. Results from the CHRISTINE 3D code are shown to compare very favorably with measurements of output power, efficiency, and interception current vs. drive power. Its predictions for spent beam distributions also compare very well with measurements. Run times for the code are problem dependent, but for a single case of interest are typically 1 to 5 min on a 450 MHz PC, orders of magnitude shorter than that required for a comparable 3D particle-in-cell simulation.

18.1: On the Minimization of Flicker and Image Retention in Silicon Light Valves

AbstractThe Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong We have performed a systematic characterization of flicker and image retention in silicon light valves. It was found that there were four mechanisms accounting for the flicker and image retention. These four mechanisms were residual DC charge on silicon surface, voltage holding ratio of the LC cell, voltage holding ratio of the silicon panel, and parasitic capacitor coupling. Causes of these mechanisms were identified and solutions for the minimization of flicker were found for each mechanism. Among these solutions, the frame rate multiplication was the most useful for all these four flicker mechanisms.

Inverters—critical photovoltaic balance‐of‐system components: status, issues, and new‐millennium opportunities

The balance-of-system (BOS) components in a photovoltaic (PV) installation include the array structure, trackers, ac and dc wiring, overcurrent protection, disconnects, interconnects, inverters, charge controllers, energy storage and system controllers. The inverter (sometimes called power-conditioning subsystem (PCS), power conditioner, or static power converter) is the key electrical power handling component of a photovoltaic power system that is attached to ac loads. This paper focuses on the inverter and its related functions as the critical electrical BOS element in a photovoltaic system. The paths that have been taken to arrive at today's inverter technology are summarized and developments in integrated hardware, advancements in packaging, advancements in manufacturing, and opportunities for the new millennium are presented. Published in 2000 by John Wiley & Sons, Ltd.

Inverters?critical photovoltaic balance-of-system components: status, issues, and new-millennium opportunities

The balance-of-system (BOS) components in a photovoltaic (PV) installation include the array structure, trackers, ac and dc wiring, overcurrent protection, disconnects, interconnects, inverters, charge controllers, energy storage and system controllers. The inverter (sometimes called power-conditioning subsystem (PCS), power conditioner, or static power converter) is the key electrical power handling component of a photovoltaic power system that is attached to ac loads. This paper focuses on the inverter and its related functions as the critical electrical BOS element in a photovoltaic system. The paths that have been taken to arrive at today's inverter technology are summarized and developments in integrated hardware, advancements in packaging, advancements in manufacturing, and opportunities for the new millennium are presented.

Implication of DC-space-charge-induced velocity spread on gyrotron gun performance

The confinement of mirror-trapped electrons under the influence of dc space charge and their effect on the velocity distribution in a magnetron injection gun is investigated theoretically and computationally. Most trapped electrons are found to escape from the gun due to pitch angle scattering by the spatially periodic electrostatic potential created by the forward propagating beam. However, a small portion scatters into orbits which are more deeply trapped and can escape only by striking the modulation anode. As electrons diffuse in velocity, the velocity distribution in the gun region extends toward increasing perpendicular velocity. On the other hand, the accumulation of trapped particles near the cathode induces an additional velocity spread in the main beam. Consequently, the main beam exhibits an increased velocity spread and a reduced transverse momentum when it enters the cavity.