Current Pulse Width Research Articles

Revisiting the Calculation of the Early Time HEMP Conducted Environment

The early time high altitude electromagnetic pulse conducted environment calculation is revisited by using the transmission line (TL) theory and including high-frequency corrections that were not present in the earlier studies. Waveform salient parameters, such as the current peak, rise time, and pulsewidth, are studied as a function of a number of parameters involved in the calculation. The obtained cumulative distribution functions of the parameter probabilities are discussed and compared with the existing standards for the HEMP protection. The high-frequency correction to the TL model results in a decrease of the current amplitudes of 15-20%. For the highest currents, rise times in the range of 25 ns are obtained. A less significant impact was found in the calculation of the pulsewidth, which was increased to about 150 ns.

Variable Speed Operation of Brushless Doubly Fed Reluctance Machine Drive Using Model Predictive Current Control Technique

To accomplish an accurate and fast drive control, model predictive control (MPC) is considered as an effective control strategy nowadays. In MPC, the voltage vectors required for inverter control are evaluated considering the control objectives defined in terms of current or power or torque and flux. The optimal one is selected using an iterative prediction loop and applied in the next control interval. This form of MPC is simple in implementation and shows appreciable dynamic performance but the steady-state performance is compromised due to the limited availability of the number of voltage vectors, especially in the case of a two-level voltage source inverter. The present article explores the viability of the MPC approach for a new candidate such as a brushless doubly fed reluctance machine drive considering its secondary current as the control variable. Moreover, to tackle the steady-state inferiority issue, the duty-cycle control concept is inducted. In comparison to field-oriented control (FOC), the proposed scheme offers a straightforward solution for current control by replacing the inner current proportional-integral controllers and pulsewidth modulator with an optimization-based model predictive current controller. An extensive simulation study in MATLAB, vis-à-vis comparison with FOC scheme, and experimental validations justify the claims of the proposed work.

Performance Degradation of Automotive Power MOSFETs Under Repetitive Avalanche Breakdown Test

Avalanche ruggedness is one of the key factors for safe and reliable power converters deployed in various automotive subsystems. In this article, the avalanche capability of power MOSFETs is tested under different repetitive avalanche conditions to differentiate the die degradation and package degradation. While examining the degradation mechanisms, the corresponding electrical parameter shifts are analyzed to better understand the structural changes and root causes and identify potential precursors for condition monitoring. For this purpose, a high-resolution and cost-effective nanosecond current pulse generator (CPG) is designed. Due to the high-resolution pulsewidth modulation function of a digital signal processor (DSP), short current pulses can be generated in the order of 100 ps where the magnitude and duration of the current pulsewidth can be adjusted precisely. During the experiments, power MOSFETs are stressed under two different pulsewidths. It is observed that the ON-state resistance gradually increases in both cases, yet the roots of the degradations are different. The die degradation and package degradation are responsible for the changes in short pulse and long pulse, respectively. In the short pulse case, some devices show saturation in drain leakage current and ON-state resistance, while some others show a significant threshold voltage drop, which leads to a noticeable shift of transfer and output characteristics. The electrical parameter shifts indicate a possible gate degradation after the device aging. At the end of the tests, failure analyses are conducted on both devices under test (DUTs) under different stress conditions, revealing different failure mechanisms.

Development of Shunt Active Power Filter for Harmonic Reduction using Synchronous Reference Frame with Space Vector Pulse Width Modulation

The work aims at development of Shunt Active Power Filter (SAPF) for harmonic reduction. The current harmonics are being caused by nonlinear characteristic of power electronics based equipments which increase power losses and in turn reduce power quality. Synchronous Reference Frame (SRF) was used as a control strategy and for reference harmonic current generation and Space Vector Pulse Width Modulation (SVPWM) was adopted as switching signal generation. With RL load under balanced input voltage condition, the developed SAPF-SVPWM achieved a reduction of THD of 0.91% as compared to 25.60 before compensation. In addition, the developed SAPF- SVPWM model was compared with SAPF without compensation using RL load under unbalanced voltage and the result shows that the developed SVPWM achieved reduction in THD of 1.74 % as compared to 26.68% after and before compensation. The developed SVPWM model was also compared with SPWM balanced and unbalanced voltage condition. The results show that SVPWM performed better than SPWM. All the results obtained are within IEEE 519 harmonics standard (i.e. THD less than 5%) with nonlinear load under balanced and unbalanced voltage.
 Keywords: Shunt active filter, input voltage, harmonics, space vector pulse width modulation, nonlinear load.

Modular solid‐state pulse generator based on multi‐turn LTD

A modular solid-state pulse generator based on a multi-turn linear transformer driver (LTD) is designed for the application of pulse power techniques with a high voltage, large current and wide pulse width. The LTD adopts the method of multi-turn winding on the magnetic core, which can help to output pulses of wide width. The isolation of the power supply with windings in the same direction of the LTD modules is designed, and the isolation voltage of the magnetic cores is the working voltage of the LTD modules. A modular solid-state pulse generator based on the multi-turn LTD is developed, which is composed of 10 LTD modules. Each module consists of 18 energy storage capacitors, metal-oxide-semiconductor field-effect transistors and their driving circuits connected in parallel. The pulse generator can output pulses with parameters including a voltage ranging from 0 to 5000 V, a pulse current up to −500 A, and a pulse width ranging from 200 ns to 5 μs. When all modules work in synchronisation, rectangular pulses can be produced with a rise time of 30 ns and a fall time of 16 ns. If all modules are asynchronised, trapezoidal pulses are produced with adjustable step-like rising and falling edges. Moreover, a higher-voltage pulse can be achieved by increasing the number of LTD modules.

Characterization of the Interdependence Between the Light Output and Self-Heating of Gallium Nitride Light-Emitting Diodes

Abstract With the advent of gallium nitride (GaN) as an enabling material system for the solid-state lighting industry, high-power and high-brightness light-emitting diodes (LEDs) with wavelengths ranging from near ultraviolet to blue are being manufactured as part of a tremendously large and ever-increasing market. However, device self-heating and the environment temperature significantly deteriorate the LED's optical performance. Hence, it is important to accurately quantify the LED's temperature and correlate its impact on optical performance. In this work, three different characterization methods and thermal simulation were used to measure and calculate the temperature rise of an InGaN/GaN LED, as a result of self-heating. Nanoparticle-assisted Raman thermometry was used to measure the LED mesa surface temperature. A transient Raman thermometry technique was utilized to investigate the transient thermal response of the LED. It was found that under a 300 mW input power condition, self-heating is negligible for an input current pulse width of 1 ms or less. The temperature measured using nanoparticle-assisted Raman thermometry was compared with data obtained by using the forward voltage method (FVM) and infrared (IR) thermal microscopy. The IR and Raman measurement results were in close agreement whereas the data obtained from the widely accepted FVM underestimated the LED temperature by 5–10%. It was also observed that an increase in environment temperature from 25 °C to 100 °C would degrade the LED optical power output by 12%.

Analysis and Experiment on Performance Improvement of IPPS at Low Temperature

The performance of inductive pulsed power supplies (IPPSs) is limited by excessive joule heat loss and low energy transfer efficiency. A significant reduction in the coil resistance can fundamentally ameliorate this problem. This article takes the meat grinder with self-charge capacitor and thyristor (SECT) circuit as an example to study the performance improvement caused by the reduction of the coil resistance. The influence of coil resistance on several performance indexes is analyzed by circuit analysis and simulation. Then, the experiment with an energy level of 40 kJ is carried out, in which the inductors have very low resistance due to immersion in liquid nitrogen. With low temperature, the charging energy and the output current peak value are increased by 37% and 19%, respectively, the pulsewidth of output current is increased by 257%, and the energy transfer capacitor is successfully self-charged compared to the performance of the same SECT circuit with room temperature. Thus, the feasibility of applying nitrogen cooling to IPPS is validated.

Simulation analysis of thermal management of inductor applied to pfn under continuous discharge condition

The pulse forming network (PFN) is an important component of the electromagnetic launch system, and its continuous discharge performance at same frequency is of great significance for the development of electromagnetic launch system. Pulse inductor is one of the key components of PFN, which has a decisive influence on the amplitude, pulse width and wave front time of discharge current. In order to study the thermal management scheme that could meet the temperature control requirements of pulse inductors under continuous discharge condition, an electromagnetic-thermal-fluid coupling model is established, and the temperature change of pulse inductor under the condition of liquid cooling and natural cooling is analyzed. It is concluded that the natural cooling scheme cannot meet the temperature control requirements, while the liquid cooling scheme can meet it. But the disadvantage of the liquid cooling scheme is that the maximum temperature difference inside the inductor will be increased.

Effect of Electropulsing on Microstructure and Properties of Severely Plastically Deformed Pure Copper Sheet

The plasticity of a material generally decreases after grain refinement by severe plastic deformation (SPD). In this paper, an energy-efficient electropulsing method is introduced to improve the plasticity of materials formed by the repetitive roll-bending and straightening (RRBS) process. The influence of the current density, frequency, pulse width and duration on the microstructure and properties of copper sheets that underwent SPD was experimentally investigated. The experimental results show that electropulsing reduced the hardness of the material, improved the plasticity and refined the grains. After the electropulsing treatment, the maximum elongation of the pure copper sheet that underwent a 20-pass RRBS process increased from 3.70 to 24.45%, and the average grain size was refined from 60 to 41 μm. The electropulsing parameters, such as the current density and frequency, instantaneously changed the incoming current intensity into the samples and had a significant influence on the microstructure and properties of the materials. The thermal effect and the athermal effect impacted the dynamics and thermodynamics of the materials, which promoted the movement of dislocations, causing significant changes in the microstructure and properties of the material in a short time.

Energy‐Efficient Ultrafast SOT‐MRAMs Based on Low‐Resistivity Spin Hall Metal Au0.25Pt0.75

AbstractMany key electronic technologies (e.g., large‐scale computing, machine learning, and superconducting electronics) require new memories that are at the same time fast, reliable, energy‐efficient, and of low‐impedance, which has remained a challenge. Nonvolatile magnetoresistive random access memories (MRAMs) driven by spin–orbit torques (SOTs) have promise to be faster and more energy‐efficient than conventional semiconductor and spin‐transfer‐torque magnetic memories. It is reported that the spin Hall effect of low‐resistivity Au0.25Pt0.75 thin films enables ultrafast antidamping‐torque switching of SOT‐MRAM devices for current pulse widths as short as 200 ps. If combined with industrial‐quality lithography and already‐demonstrated interfacial engineering, an optimized MRAM cell based on Au0.25Pt0.75 can have energy‐efficient, ultrafast, and reliable switching, for example, a write energy of <1 fJ (<50 fJ) for write error rate of 50% (<10−5) for 1 ns pulses. The antidamping torque switching of the Au0.25Pt0.75 devices is ten times faster than expected from a rigid macrospin model, most likely because of the fast micromagnetics due to the enhanced nonuniformity within the free layer. The feasibility of Au0.25Pt0.75‐based SOT‐MRAMs as a candidate for ultrafast, reliable, energy‐efficient, low‐impedance, and unlimited‐endurance memory is demonstrated.

Power Supply System Design and Dynamic Analysis of a Permanent Magnet Bistable Electromagnetic Clutch for Wheel Motor Drive

In-wheel motor is recognized as the ideal form for electric vehicle drive. To reduce the mechanical shock and the electromagnetic impulsion brought by the rigid connection between the hub and the motor, a permanent magnet bistable electromagnetic clutch which flexibly connects the motor and the hub is proposed. In this paper, several power supply schemes for the clutch are discussed. Firstly, based on the dynamic simulation model, the static and dynamic performances of the clutch unit are studied, and then the advantages and disadvantages of these power supply systems are compared. Furthermore, the capacitor discharge pulsed power supply defined as “rotor side harmonic power generation + rechargeable battery + clutch wireless remote control” is intensively investigated. Based on the proposed analytical solution of the current pulse width, the optimal design is carried out, the capacitance, charging voltage, coil turns, and coil wire diameter is determined. Finally, experimental results verified the effectiveness of these power supply systems and the rationality of design.

Plasma Species and Coating Compositions in Aluminum Treated by PEO Using Shot Square Pulse

Abstract Up to now, plasma electrolytic oxidation (PEO) has been either produced direct current or ultra-low frequency ( 8 g.L-1 with presence of KOH). In order to contribute to these studies, the effect of current pulse width and time duration was investigated using diluted silicate electrolytic (Na2SiO3 2 g.L-1) and high pulse frequencies (> 1 kHz). The PEO process was performed on pure aluminum to try to explain how the phases composing the coatings are formed and distributed over the treatment time. For this, was made in situ monitoring using optical emission spectroscopy (OES) coupled with CCD camera. The crystalline phases evolution in the sample surface was investigated using grazing incidence X-ray diffraction (GIXRD). Regarding the evolution of ceramic phases, it is possible to verify that, internally, the predominant phase is rhombohedral α-Al2O3 but, superficially, the predominant phase is cubic γ-Al2O3. It was verified the presence of Si on the borders of the pores or in proximity to cracks, especially in the treatments with higher pulse width. SEM analysis shows a reduction of the superficial porosity and an increase in coating thickness with pulse width and treatment time.

Boron vacuum-arc ion source with LaB6 cathode.

We describe a pulsed vacuum arc ion source with a lanthanum hexaboride (LaB6) cathode for high-dose selective implantation of 10B and 11B isotope ions. The design and main parameters of the source and its plasma generator are described, and research data are reported on the formation, transport, and magnetic separation of 10B and 11B ions extracted from the erosion plasma of a vacuum arc discharge. Cathode spots are initiated by flashover across an alumina ceramic block of diameter ∼2.5 mm located at the center of the working cathode. The design of the trigger system provides rather uniform cathode erosion, and the cathode dimensions (diameter of 14 mm, length of ∼15 mm) ensure long-term operation of the source. The plasma generator operates at a pulse repetition rate of up to 10 Hz with a discharge current pulse width of 280 µs. At an arc current of 130 A, the source provides an ion beam of a rectangular cross section of 0.6 × 6 cm2 with an energy of 25 keV and amplitude up to 75 mA. A mass analyzer magnet was used for mass-to-charge separation.

Implementation of the Zero Current Transition PWM Boost Converter using Digital Signal Processor

There are various solutions for reducing turn-off loss of insulated gate bipolar transistor (IGBT). The ‘zero current transition pulse width modulation’ (ZCT-PWM) technique is one of them. For ZCT-PWM technique, the gate signal of auxiliary switch, which is synchronized to the gate signal of main switch is needed. This paper describes the implementation of both gate signals which is comprised of the main switch and the auxiliary switch using a digital signal processor (DSP), and 300-W ZCT-PWM boost converter is designed and implemented to verify ZCT technique.

Preparation of thin NiCrBSi laser cladding layers with no microcracking and low dilution

To further extend the application of laser cladding, trials to prepare thin NiCrBSi layers by laser direct cladding were conducted using common Nd:YAG laser equipment in this study, and the influence of main processing parameters on the cladding quality and melting of the substrate was investigated. The results reveal that using coarse powder, solidification microcracks appear at the center of the melting pools, with some alloy drops on the as-cladded surface. After remelting, most of the drops can be melted, and the surface becomes flatter. When the laser pulse frequency is high enough, the microcracks can be completely eliminated by the next laser spot; then, a cladding layer of about 150 μm thick is obtained, while melting of the substrate and fusion between the cladding alloy and the substrate are still obvious. Using a finer powder that has a higher light absorption rate, thinner (∼100 μm) and uniform cladding layers with no microcracking can be obtained without remelting, and melting of the substrate is far less serious. All the thin cladding layers show much higher microhardness than the substrate, and the heat effect on the microstructure of the substrate is not obvious. High scanning speed, enough current, and short pulse width are suggested to get high quality thin cladding layers.

Characteristics of N<inf>2</inf>/O<inf>2</inf> reaction in spark gap switch: The effect of high-current pulsed arc

Compressed air is used in spark gap switches as an insulating gas. Triggered by nanosecond pulsed voltage, the streamer bridges the electrode gap in the switch. During the streamer-arc transition, the spatial distribution of the arc changes drastically. The nitrogen and oxygen in the compressed air will react with each other under high temperatures. Damaging effects in the switch are caused by arc reaction. In this paper, by adjusting the parameters of the high-energy pulse discharge circuit, the arc is produced with different current waveform in the spark gap switch, while the gaseous product is analyzed. The results show that, when current pulse-width remains constant, the amount of transferred charge is approximately linear with the production of nitrogen oxides. The proportion of NO is higher when the current pulse-width is shorter. The concentration of nitrogen oxides is determined by the chemical reaction, which relies on the dynamic change of the impulse arc. During the arcing time, there is the collision dissociation reaction in the local thermodynamic equilibrium (LTE) plasma, leading to the production of gas atoms and excitation molecules. In the boundary of the arc channel, the nitrogen oxides formation reactions mainly occur in the arc quenching period. According to the characteristics of the high-current arc, a simplified analysis of chemical kinetics on the reactions of nitrogen and oxygen is implemented to expound the effect of pulsed arc on the gas composition.

Transient Temperature Field Analysis of Thyristor Turn-on Process under Narrow Pulse Width and Large Current

Thyristor will damage because of local overheating under narrow pulse width and large inrush current, if the selection is unreasonable. In this paper, the thermal field model of thyristor opening process is established and the transient temperature field distribution of thyristor is obtained by simulation. Simulation results show that under the narrow pulse width and large current, the temperature distribution on the silicon chip is not uniform, the temperature at the center gate is the highest, and the temperature is gradually decreased from the center point along the radius. The effect of current rise rate and chip radius on thyristor temperature distribution are simulated. Simulation results show that the higher the current rise rate, the higher the temperature of the thyristor center gate. The effect of chip radius on thyristor temperature is related to the pulse width of large inrush current. When the chip radius is smaller than the extended radius corresponding to the current pulse width, the smaller the radius, the higher the maximum temperature rise. When the radius of the chip is equal to or greater than the extended radius corresponding to the current pulse width, increasing the radius of the chip has no effect on the highest temperature rise.

Thermally activated magnetization back-hopping based true random number generator in nano-ring magnetic tunnel junctions

A true random number generator based on the magnetization backhopping process in nano-ring magnetic tunnel junctions is demonstrated in this work. The impact of environmental temperature (T) and current pulse width (τ) on backhopping is investigated statistically by experiments, micromagnetic simulations, and theoretical analysis. The backhopping probability increases at high T and wide τ, as explained by the combined effect of thermal fluctuation and spin-transfer-torque noise. The magnetoresistance at backhopping is randomly distributed over a large operational current range. This manifestation of backhopping in magnetic tunnel junctions can be used as the basic unit of a true random number generator.

Unpredictable Bits Generation Based on RRAM Parallel Configuration

In this letter, a cell with the parallel combination of two TiN/Ti/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /W resistive random access memory (RRAM) devices is studied for the generation of unpredictable bits. Measurements confirm that a simultaneous parallel SET operation in which one of the two RRAMs switches to the low-resistance state is an unpredictable process showing random properties for different sets of cells. Furthermore, given a device pair, the same device switches during subsequent write operations. The proposed cell is also analyzed under different current compliances and pulse widths with the same persistent behavior being observed. The features of the proposed cell, which provide data obfuscation without compromising reliability, pave the way for its application in physical unclonable functions for hardware security purposes.

Spin-orbit torque-induced switching of in-plane magnetized elliptic nanodot arrays with various easy-axis directions measured by differential planar Hall resistance

Spin-orbit torque-induced switching of an elliptical nanomagnet with an in-plane easy axis allows sub-ns and field-free operation. Since its properties crucially depend on the design of the nanomagnet such as the easy-axis direction, it is of high importance to systematically elucidate the dependence of performance on various parameters of the nanomagnet towards magnetoresistive random access memory applications. Here, we show a scheme to statistically evaluate the switching properties of in-plane nanomagnets in a short turnaround time. We use devices with an array of CoFeB/MgO nanomagnets formed on a cross-shaped Ta/W Hall bar, and the differential planar Hall resistance is measured to study the magnetization switching. Using the scheme, we investigate the easy-axis angle dependence of switching properties at zero magnetic fields for various current pulse widths from 100 ms to 1.7 ns. We show that the dependence of threshold switching current on the easy-axis direction significantly varies with the pulse width.