Initial Capacitor Voltage Research Articles

Capacitor Pre-Charge Method for Back-to-Back Seven-Level Hybrid Clamped Converter Without Extra Power Supply

Multilevel converters with floating capacitors generally require precharging to build up the voltage on floating capacitors and dc-link before the normal operation. In particular, precharge is challenging for converters with overvoltage concerns under initial zero capacitor voltages. As a promising topology, seven-level hybrid clamped (7L-HC) converters also require precharge of capacitors and shall avoid high voltage stress during the precharge. Considering the high cost of deploying extra dedicated precharge circuits in a medium voltage system, the precharging method without relying on dedicated power supplies is favored. In this article, specific switching states and their corresponding selection schemes are designed to precharge floating capacitors of back-to-back 7L-HC converters. In this process, the inrush current and voltage stress can always be limited in the safe range. This method only needs series and shunt resistors typically already exist in practical converter circuits, resulting in low cost and ease of implementation. The design method of the resistances is also provided. Both simulation and experimental results validate the feasibility of this method.

Preliminary Analysis and Simulation of a 20-Hz Repetitive Superconducting Pulsed Power Supply

Superconducting pulsed power supplies (SPPSs) have attracted more and more attention because of their advantages of high energy storage density, long energy storage time, low loss, and low power requirements for charging power sources. In order to improve energy efficiency and output continuous pulse currents, a 20-Hz repetitive SPPS based on high temperature superconducting pulsed power transformer (HTSPPT) and residual energy recovery method is proposed and researched in this article. The main principle is that the residual energy is recovered and used for the next cycle of the repetitive SPPS for improving energy efficiency, shortening the charging time, and increasing the operating frequency. The working principle and procedure of the repetitive SPPS are introduced and analyzed in detail, and simulations are carried out to study the characteristics of the repetitive SPPS. The effects of the initial capacitor voltage and the switching trigger time of each cycle on the output characteristics are analyzed. The simulation results show that the repetitive SPPS with personalized trigger time can output a stable repetitive pulse current, that is, the output characteristics are stable.

Modeling of the exploding foil initiator and related circuitry for the variable mode of operation

Analytical and numerical models, validated against published data, were developed to calculate the velocity and time of arrival duration (ToAD) of the flyer-plasma material at the top of the barrel of an exploding foil initiator (EFI), as commonly used in explosive devices. Such tools will aid system designers in the optimization of capacitor discharge circuit (CDC) or EFI bridge material properties. The analytical elements of the approach developed support the requirement for the consideration of mass ejection variation with respect to initial capacitor voltage. The numerical elements of the approach developed demonstrate that EFI design alteration to increase flyer mass is less effective in reducing ToAD than supply voltage modulation via the CDC. This finding is of particular relevance for in situ control of functional performance characteristics. This work goes on to demonstrate that such control is impracticable when using hexanitrostilbene, since the initial capacitor voltages necessary to yield appropriate ToAD for deflagration deliver insufficient energy to instigate a response from the EFI.

Energy Transfer Efficiency Optimization in an Electromagnetic Railgun

Electromagnetic railguns (EMRs) launch projectiles by the systematic triggering of current pulse forming units (PFUs), which release stored capacitor energy. Past work has focused on maximizing projectile velocity at the muzzle for given PFU capacitor charge voltages, which maximizes efficiency. However, operators in naval applications need to be able to select the muzzle velocity for a projectile to achieve a desired ballistic path. Thus, there is a demand to maximize efficiency for a given muzzle velocity. As such, this paper investigates maximizing the efficiency of transferring the stored PFU capacitor electrical energy to projectile kinetic energy while minimizing the current value when the projectile exits the rails to reduce damage to them from arcing. This is accomplished by optimizing the choice of the initial capacitor voltage in each PFU and the trigger timing subject to an electrical-mechanical dynamic model of the EMR and projectile and any additional scenario constraints (described shortly). This optimization is solved using numerical programming in the context of a relaxation with the initial capacitor voltages and triggering times as the only explicit variables to the optimizer; additional needed values are obtained from a differential algebraic equation solver. The optimization is successfully demonstrated for three scenarios: operation for a projectile mass and muzzle velocity associated with published operating parameters, operation for several projectile mass-muzzle velocity pairs with both equal and distinct initial capacitor voltages, and operation for several projectile mass-muzzle velocity pairs with a load current bound and equal initial capacitor voltages. Results show improved efficiency in comparison to the use of the published parameters, the independence of efficiency from projectile mass when there is no current bound, virtually identical results for equal and distinct initial capacitor voltages, and decreased efficiency with a current bound.

Temporal shock wave analysis produced by copper exploding wires in air at atmospheric pressure

In this work, experimental results concerning the temporal evolution of the shock wave radii generated by an exploding copper wire of fixed length are presented. The variables of the experience were the diameter dimension—from 50 to 500 μm—and the initial capacitor voltage—from 5 to 25 kV. The diagnostic device was a streak shadow image system synchronized with the experiment. The result is a parametric collection of data showing the shock wave position across the time depicting the different stages of the experience.

Electrical Characteristics of Pulsed-Discharge Plasma for Decoloration of Dyes in Water

The electrical characteristics of pulsed-discharge plasma for decoloration of dyes in water were systematically investigated with a view toward getting insight into discharge process. Methylene blue (MB) dye water was selected as the target object. The discharge behavior was found to depend on the power supply voltage, conductivity of MB solution, and pulse-forming capacity. A strong positive linear relationship existed between power supply voltage and initial capacitor voltage. The injection energy per pulse increased when increasing the power supply voltage and a maximal energy efficiency of injection of approximately 85% was obtained at power supply voltage of 50 V. The conductivity of MB solution had appreciable impact on the voltage-current characteristics and discharge time of pulse-forming capacitor. Remarkable increase of pulse current was observed as the pulse-forming capacity increasing, while it had slight effect on the pulse voltage. The pulsed corona discharge in MB solution could change into spark discharge by way of increasing the air flow rate and reducing the electrode distance. Increasing pulse-forming capacity and pulse frequency significantly accelerated the decoloration rate of MB in solution. This paper is expected to provide reference for improving the application of pulsed-discharge plasma in treating dye solution.

Experiment and Research of Energy Depositing Rate of Exploding Wires Under Different Initial Capacitor Voltages for Thin Film Production

Thin film produced by exploding wires is affected by many factors; one of such factors is the energy depositing rate. The research in this paper focused on measuring the voltage and current of an exploding copper wire that was 15 cm long and 0.3 mm in diameter. The time-dependent wire resistance and the energy deposited into the wire were deduced from the measured voltage and current, and the maximum wire resistance was observed at the time when part of the wire mass was heated up to the boiling point, which was called critical time and critical point, respectively. From the experiment, the following statements could be surmised: The maximum wire resistance increases from about 224.4 to 266.1 mΩ, and the critical time reduces from about 8.8 to 7.2 μs when the initial capacitor voltage changes from 10 to 20 kV, as well as the fact that the mean energy depositing rate varies from about 13.3 to 27.6 J/μs before the critical point. Also, thin copper film is prepared by this method under initial capacitor voltages of 10,15, and 20 kV, respectively. The SEM micrographs of the film samples are also presented and analyzed. This result demonstrates that a faster energy depositing rate can help to heat up the wire mass more uniformly and more wire mass would evaporate before the critical time to create a greater wire resistance at the critical point, and the film surface is more uniform and has less void fraction.

Dynamics Modeling of Fast Transformer Type Fault Current Limiter Loaded With HTSC

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Theoretical model of the fast fault current limiter based on an air core transformer, the secondary winding of which is loaded with high-<emphasis><formula formulatype="inline"><tex>$T_{c}$</tex></formula></emphasis> superconductor (HTSC) sample, has been analyzed. The fault current limiter was designed to protect a strong magnetic field pulse generation system. Transformer parameters and HTSC sample resistance in the normal state have been chosen to provide the fault current limitation efficiency. The current limiting dynamics was investigated by solving nonlinear system of equations. A detailed explanation of the results is presented. It is shown that application of the fault current limiter allows us to increase the initial reservoir capacitor voltage of the protected system up to 2.6 times. </para>

Comparison of the energy performance of pulse generation circuits for PEF

Pulse shaped voltages are required for preservation of food with PEF. Several pulse forms generated by a variety of circuits are compared with respect to required energy. The analysis includes square pulses, trapezoidal pulses, exponential decay pulses and oscillatory and over-damped oscillatory pulses. The base of comparison is the establishment of a certain minimum voltage level during certain minimum time. The comparison concerns the dissipation in a resistive load, which is considered to be representative for a category of loads, including PEF. Furthermore, the ratio between initial capacitor voltage and corresponding threshold voltage is compared as this parameter reflects the required hold voltage of the switch in the circuit. The analysis shows that the efficiency approaches 100% for hard switched circuits and circuits with transmission lines. For highly damped RLC-circuits with capacitor C, inductor L and load resistance R the maximum obtainable efficiency is between 37 and 47% where the capacitor C has to be charged to 1.6–1.8 times the desired threshold voltage. For oscillating damped sinusoids the maximum efficiency is between 47 and 52%, however, the capacitor has to be charged to 1.8–3 times the threshold voltage. Graphs with an example are provided to determine circuit parameters from a certain pulse specification.

Generation of multiply charged ions from a cathode jet of a low-energy vacuum spark

Ion parameters in a cathode plasma jet of a vacuum spark with a discharge energy of a few joules were measured. The studies were performed by a time-of-flight method with the help of an energy analyser. It was found that the discharge plasma generated a short-run beam of multiply charged ions of the cathode material at the initial stage of the discharge firing. The ions had charge states from Z = + 1 up to Z = + 18. When the initial capacitor voltage was varied within the ranges of 0.3-2.5 kV, the mean ion charge increased from +4.3 to +9.0.

Minimal transient switching of capacitors

Capacitor banks are used to compensate the reactive power demand of large commercial and industrial loads. When used to switch capacitor banks mechanical breakers generate large current transients. These transients may cause serious system disturbances, premature wear of the breaker contacts and, possibly, shorten the life of the capacitors. While thyristor switches are not new and industry has successfully used them to obtain transient-free switching of capacitor banks, there are very few papers describing this application. This paper tries to fill the void and presents a comparative study of various three-phase configurations of semiconductor switches intended for low voltage (600 V and less) distribution systems. Simple theoretical analysis enables the calculation of the optimal switching times to minimize transients. These calculations take into account the system impedance and the initial capacitor voltages. >

Undegassed and Degassed Exploding Tungsten Wires in Vacuum

Undegassed and degassed tungsten wires, initially coated with an impurity layer of tungsten oxide and graphite, have been exploded in a vacuum of 2×10−6 Torr and at an initial capacitor voltage of 20 kV. Correlated x-ray and electrical measurements of these wires indicate that the x-ray emission from the wires begins prior to the appearance of the shunting discharge. The hard x-ray burst emitted has a half-amplitude width of about 25×10−9 sec and is reproducible from explosion to explosion provided the initial conditions are identical. The emission of hard x rays but not the main discharge current is influenced by the gases initially adsorbed by the wire surface. Finally, the main discharge current, but not the emission of hard x rays, is influenced by the impurity layer.

Studies of characteristic flash X-ray lines

Time resolved spectroscopic detection of characteristic X-radiation as well as Bremsstrahlung from flash X-ray discharges and simultaneous recording of thedI/dt waveform showed that both kinds of X-radiation were produced duringdI/dt minima. The MoKα1 line could be detected with an initial capacitor voltage right down to only 70 per cent of the excitation potential. The investigation supports the theory that the plasma in the flash X-ray discharge is pinched, causing high voltages in the discharge

Fundamental Study on Electrohydraulic Forming : II. The Effect of Kinds of Fuse Wires and Circuit Inductance on Pressure Pulse

There have been many studies on electrohydraulic forming in which the relationship between the deformation characteristics of metallic material of a given shape and the stored electrical energy is investigated, but few studies on pressure pulse which has direct relation with the deformation. In a previous paper the authors presented a fundamental study on this relation within the stored electrical energy up to 180 J. This paper presents the investigation, in which a capacitor discharge circuit employed as an electrohydraulic forming machine is used to explode various kinds of fine wire (diameter : 0.20 mm, length : 5 cm) submerged in a water tank, and the resulting pressure pulse at a position 15 to 50 cm from the pressure source is measured as a function of time using a calibrated gage (barium titanate) and an oscilloscope. The effects of various kinds of fine wires and discharge circuit conditions, such as initial capacitor voltage and inductance, on the shape and amplitude of pressure pulse are presented, and the efficiency of these apparatus is also mentioned and discussed. Initial capacitor voltage is varied up to 11 kV, and the total stored electrical energy in the capacitor bank is varied up to 1400 J.

Pinch Phenomena in a Flash X-ray Discharge

The discharges were performed in a coaxial flash x-ray tube (voltage = 15 kv, pressure = 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> mm Hg and inductance = 75 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> h) provided with a plane parallel electrode system. The discharge process has been studied by oscillographic recordings of any pair of the three quantities: current, its time derivative and x-ray output, inside the time interval during which the heavy current pulse (peak current about 25 ka) occurs in the discharge. The production of both single and multiple x-ray outputs of short duration (0.1 μsec or less) is discussed and seems to be caused by pinch phenomena occurring in a plasma column between the tube electrodes. Small changes in dI/dt during the pinching are interpreted as sausage instabilities which cause high local rates of increase in inductance giving a potential drop (V = I dL/dt) across each constriction of the discharge. Estimation of the accelerating voltage during the pinching showed that it could reach values almost four times as high as the applied initial capacitor voltage. In order to get the timing of the x-ray outputs under better control, a new method for discharge initiation is suggested.

Fundamental Study on Electrohydraulic Forming : II. The Effect of Kind of Fuse Wire and Circuit Inductance on Pressure Pulse

There were many studies on electrohydraulic forming in which the relationship between the deformation characteristic of metallic material of a given shape and stored electrical energy was investigated, but few studies on pressure pulse which had direct relation with the deformation. In the previous paper the authors presented a fundamental study on this relation within the stored electrical energy up to 180 joules. This paper presents the results of experiments, in which a capacitor discharge circuit employed as an electrohydraulic forming machine was used to explode various kinds of fine wire (diameter : 0.2mm, length : 5cm) submerged in a water tank, and the resulting pressure pulse at a point 15 to 50cm from the pressure source was recorded as a function of time using a calibrated pressure gage (barium titanate) and an osciloscope. The effect of various kinds of fine wire and discharge circuit conditions such as initial capacitor voltage and inductance on the shape and amplitude of pressure pulse is presented, and the efficiency of these apparatus is also mentioned and discussed. Initial capacitor voltage was varied up to 11 kV, and total stored electrical energy in the capacitor bank was varied up to 1400 joules.

Fundamental Study on Electrohydraulic Forming : III. The Effect of Dimension of Fuse Wire and Circuit Inductance on Pressure Pulse

There were many studies on electrohydraulic forming in which the deformation of metallic material was investigated. In most of the studies the wire used as pressure source is very fine. A clear account has not been given of the relationship between the dimension of wires and initial discharged circuit conditions such as initial capacitor voltage and circuit inductance, and then at a given stored electrical energy there is little reason to use what kind and dimension of wires as effective pressure source. For the reason of F.H. Webb's experimental fact that, if sufficient energy is accumlated into wire to vaporize it, the delaying time of boiling lasts for a time comparable with the time required for a sonic wave in the wire to propagate to the center and return, the longer the time just described is, the higher superheating is. This paper presents the results of experiments in which the characteristic of capacitor discharge circuit as electrohydraulic forming machine was used to explode fine copper wire of which diameter is 0.14 to 0.4mm. The best condition for creation of pressure pulse is investigated and discussed.