Turn-off Time Research Articles

Design of Cost Effective Solar PV Powered SRM Driven Agriculture Pump Using Modified Buck-Boost Converter

Abstract This paper proposes a new DC-DC converter for performance optimization of a solar PV(Photovoltaic) system without electrolytic capacitor for water pumping system driven by a switched reluctance motor (SRM). The proposed converter is able to replace the input electrolytic capacitor to polypropylene capacitor with small rating and size. The snubber circuit formed by storage capacitor across switch of converter is operated to minimize the voltage spikes especially during turn-on and turn-off time. The proposed DC-DC converter delivers a continuous supply to SRM drive with low ripple content and capable to step-up and step-down the input PV voltage. The PV power optimization and to limit the high initial winding currents of SRM, are two major functions of proposed converter. An improved perturb and observation (P&O) based maximum power point tracking (MPPT) control is also proposed in present system, which overcomes the deviation problem present in conventional P&O MPPT controls. Simulated and experimental results on a 500 W four-phase 8/6 SRM, are accomplished to authenticate the feasibility of proposed system under all environmental conditions.

A Time-Domain Electromagnetic Transmitter with Great Power and Large Current by Using a Closed-Loop Phase Shifting Control Strategy

A time-domain electromagnetic transmitter (TDET) with great power and large current was designed by using a closed-loop phase shifting control strategy. A clamping voltage source circuit was applied in this system to improve the falling edge of emission current and shorten the turn-off time. The simulated results showed that this TDET exhibited the advantages including a large current, strong capability for rapid turn-off, stably output voltage, preferably dynamic performance, a widely adjustable range in transmitting voltage, accurate measurement precision.

An inversion of transient electromagnetic data from a conical source

Multiturn coils is an effective transmitter for transient electromagnetic method (TEM) used in narrow space and complex terrain at presently. However, its high mutual inductance coupling and long turn-off time affect the quality of later data processing and interpretation. Compared with multiturn coils, the new conical source has low mutual inductance and short turn-off time. Based on the superposition principle, we use Hankel transform and numerical filtering method for forward modelling of the conical source field in the layered-media and explore TEM characteristics excited by this source. We apply improved damped least square inversion to integrated transient electromagnetic (TEM) data. We first invert the induced voltage into similar resistivity and apparent depth, and then use the inverted results as input parameters in the initial model and transform the apparent resistivity data into the frequency domain. Then, damped least square inversion is performed in the frequency domain using the initial model. Subsequently, we use automated model building to search for the extremes and inflection points in the resistivity–depth data that are treated as critical layer parameters. The inversion of theoretical and observed data suggests that the method modifies the resistivity and depth and yields a model of the underground layers.

Development of High Temperature Operation SiC Power Module

We have developed SiC power module which realizes operation at high temperature of 250 °C or higher. The withstand voltage of this power module is 1200 V, and two SiC-MOSFETs are built in and constitute a circuit for one inverter phase. This power module incorporates a snubber circuit for reducing the surge voltage generated by the SiC-MOSFET during switching. Joining of the main parts in the module is done with eutectic solder with a solidus line of 350 °C or higher. It can operate at high temperatures up to 250 °C and ensures reliability at that temperature. We conducted 100 A switching test using this module. High speed switching was realized, and the turn-off switching time tf was about the same about 10 ns from room temperature to 250 °C. In this paper, we describe the design and performance of the developed power module.

Development of High Temperature Operation SiC Power Module

We have developed a Silicon Carbide (SiC) power module that can operate at high temperatures up to 250 °C. Figure 1 shows the overview of the developed power module. The withstand voltage of the power module is 1200 V, two SiC - MOSFETs are built in, and it is a circuit composition of one phase of the power inverter. The two-layer SiC-Active Metal Brazed Copper(AMC) not only reduces the area of the power module but also reduces circuit inductance. In addition, this power module has a built-in snubber circuit that reduces the switching surge voltage of the SiC-MOSFET during high-speed switching. Generally, when the power module is operated at a high temperature, the reliability such as occurrence of lowering of the main bonding strength of the power module is significantly reduced due to thermal deformation. In this power module, the main components of the module are joined using eutectic solder with a solidus line above 350 °C. Copper-tungsten (CuW) was selected as the base plate material. Since the Coefficient of Thermal Expansion (CTE) values of CuW and SiN - AMC are close, it is possible to reduce the stress applied to these joints when the temperature changes. In addition, CuW has excellent thermal conductivity and heat capacity and suppresses heat generation of SiC-MOSFET. To evaluate the performance of this module, a switching test at 100 A was performed at 250 °C. The switching waveform is shown in Fig.2. The turn-off switching time tf was about 10 ns, and the switching surge voltage at that time was about 150 V. The turn-off switching waveform was almost the same from room temperature to 250 °C. As a result, it was shown that this power module can operate at 250 °C and the built-in snubber circuit works effectively at all temperatures. Acknowledgement This work was supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), "Next-generation power electronics / Consistent R&D of next-generation SiC power electronics" (funding agency: NEDO). Figure 1

Low-Loss 800-V Lateral IGBT in Bulk Si Technology Using a Floating Electrode

An 800V rated lateral insulated-gate bipolar transistor (LIGBT) for high frequency and low-cost applications is proposed. This LIGBT features a new method of adjusting the bipolar gain by using floating N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and P <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> regions connected by a floating electrode in front of the P <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> collector. This floating structure lowers the injection efficiency at the collector side of the device, resulting in a very significant decrease in turn-off time and substantially lower turn-off losses. The device was fabricated in a 0.5μm bulk silicon CMOS technology at a commercial foundry without additional processing steps or process optimisation. Tests on fabricated devices showed equivalent Rdson below 70 mQ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 125 °C with switching times as low as 250 ns at 125 °C. The novel LIGBT device showed avalanche capability and low gate capacitance and was used for the first time, in an AC/DC converter operating at 200 kHz allowing significant improvements in performance, compactness, and reduced component count.

A Light-curve Analysis of Gamma-Ray Nova V959 Mon: Distance and White Dwarf Mass

Abstract V959 Mon is a nova detected in gamma-rays. It was discovered optically about 50 days after the gamma-ray detection owing to its proximity to the Sun. The nova’s speed class is unknown because of the lack of the earlier half of its optical light curve and a short supersoft X-ray phase due to eclipse by the disk rim. Using the universal decline law and time-stretching method, we analyzed the data on V959 Mon and obtained nova parameters. We estimated the distance modulus in the V band to be (m − M) V = 13.15 ± 0.3 for the reddening of E(B − V) = 0.38 ± 0.01 by directly comparing it with novae of a similar type—LV Vul, V1668 Cyg, IV Cep, and V1065 Cen. The distance to V959 Mon is 2.5 ± 0.5 kpc. If we assume that the early phase of the light curve of V959 Mon is the same as that of time-stretched light curves of LV Vul, our model fitting of the light curve suggests that the white dwarf (WD) mass is 0.9–1.15 M ⊙, which is consistent with a neon nova identification. At the time of gamma-ray detection the photosphere of the nova envelope extends to 5–8 R ⊙ (about two or three times the binary separation) and the wind mass-loss rate is yr−1. The period of hard X-ray emission is consistent with the time of appearance of the companion star from the nova envelope. The short supersoft X-ray turnoff time is consistent with the epoch when the WD photosphere shrank to behind the rising disk rim, which occurred 500 days before nuclear burning turned off.

The Temporal Development of Dust Formation and Destruction in Nova Sagittarii 2015#2 (V5668 SGR): A Panchromatic Study

Abstract We present 5–28 μm SOFIA FORECAST spectroscopy complemented by panchromatic X-ray through infrared observations of the CO nova V5668 Sgr documenting the formation and destruction of dust during ∼500 days following outburst. Dust condensation commenced by 82 days after outburst at a temperature of ∼1090 K. The condensation temperature indicates that the condensate was amorphous carbon. There was a gradual decrease of the grain size and dust mass during the recovery phase. Absolute parameter values given here are for an assumed distance of 1.2 kpc. We conclude that the maximum mass of dust produced was 1.2 × 10−7 M ⊙ if the dust was amorphous carbon. The average grain radius grew to a maximum of ∼2.9 μm at a temperature of ∼720 K around day 113 when the shell visual optical depth was τ v ∼ 5.4. Maximum grain growth was followed by a period of grain destruction. X-rays were detected with Swift from day 95 to beyond day 500. The Swift X-ray count rate due to the hot white dwarf peaked around day 220, when its spectrum was that of a kT = 35 eV blackbody. The temperature, together with the supersoft X-ray turn-on and turn-off times, suggests a white dwarf mass of ∼1.1 M ⊙. We show that the X-ray fluence was sufficient to destroy the dust. Our data show that the post-dust event X-ray brightening is not due to dust destruction, which certainly occurred, as the dust is optically thin to X-rays.

An Analysis of the Highly Linear Transfer Characteristics of Dual-Buck Converters

Practical switching devices have finite turn-on and turn-off times. To avoid short circuit, a blanking time is added between turn-off and turn-on of the complementary working switches in a switching-leg. The blanking time, also referred to as deadtime, is one of the dominant sources of output current and voltage distortion in pulse-width modulated (PWM) power amplifiers. Extensive studies exist on elimination, minimization, and compensation of the effect. Most techniques achieve a reduction of the distortion but are not capable of completely removing it. The dual-buck (DB) converter does not suffer from blanking-time-related distortion. However, blanking time is not the only source of switching-leg-induced distortion. This paper focuses on the effects of semiconductor device parameters on the output quality of the DB converter. It is shown that, ideally, the forward voltages of the diodes and switches have no effect on the output quality. Measurements on a prototype, industrial power stack based, DB converter show a 100 times improvement of the open-loop spurious free dynamic range when compared to conventional PWM converters.

Experimental research on improving accuracy of electrochemical machining of deep narrow grooves

Deep narrow metal grooves have wide application prospects in the field of aeronautics and astronautics. Electrochemical machining (ECM) has a unique advantage in the fabrication of deep narrow grooves due to its advantages of no cutting heat, no cutting force, and high machining efficiency. But, there is significant stray current corrosion in the side wall of the deep narrow groove, which restricts the enhancement of the processing accuracy. In the interest of improving the processing accuracy of the deep narrow groove, the effects of compound feed and matching of pulse and oscillation (MOPAO) on the average current density distribution of the deep narrow groove side wall were studied based on finite element analysis (FEA) of the electrostatic field. The finite element simulation results show that the homogeneity of the deep narrow groove could be significantly improved with the increment of the oscillation amplitude, and the processing accuracy could be improved by prolonging the pulse turn-off time. Moreover, contrast experiments on the deep narrow groove ECM were carried out based on a self-developed ECM system. The experimental results indicate that the matching of pulse and oscillation can remarkably improve the processing accuracy, and smaller average groove width and better groove width uniformity can be obtained in comparison with the compound feed. Moreover, the maximum groove width is 2.78 mm, the minimum groove width is 2.73 mm, the length-width ratio reaches 11:1, and the depth-width ratio reaches 9:1 using the machining mode of MOPAO.

Assessment of a clean and efficient fire-extinguishing technique: Continuous and cycling discharge water mist system

Abstract As the succedaneum of halon extinguishing agent, water mist is absolutely green, harmless, and sustainable which does not cause the ozone depletion. In order to investigate the fire extinguishment performance of water mist system with both continuous and cycling discharge modes, a series of full-scale pool fire suppression experiments (including gasoline and diesel) with the two discharge modes were conducted in a confined compartment (3 m × 3 m × 3 m) under different mechanical exhaust rates. Some characteristic parameters, such as the smoke temperature, radiative and total heat flux, fire-extinguishing time, and carbon monoxide and oxygen concentration under the influences of both water mist and mechanical ventilation, were obtained, and their variation mechanisms were analyzed in detail. The experimental results show that pool fires could be extinguished more quickly using cycling water mist with shorter turn-off time. The reduction coefficient of carbon monoxide concentration increases exponentially, while the extinguishing time of both gasoline and diesel pool fires decreases first and then increases with the ventilation rate. With cycling discharge mode, the smoke temperature and heat flux both fluctuate with alternate activation of water mist. The application of cycling discharge mode substantially improves the fire suppression efficiency, especially in the condition that the pool fire is difficult to extinguish utilizing continuous discharge mode. The cycling discharge water mist system can be applied in some ventilated spaces when mechanical ventilation is unavoidable, and is helpful for personnel security and evacuation.

Design of high-disturbance driver system for SiC high-power module

Compared to conventional Si power electronic device, the advantages of SiC power electronic device are high turn-off voltage, low on-resistance, high switching frequency and high efficiency. The high performance of the device is achieved by shortening the turn-on and turn-off times. However, the SiC power modules have higher dv/dt and di/dt, which leads to more CM (common mode) interference and DM (differential mode) interference certainly. In this paper, the operation principle of driver circuit is introduced firstly. Then, the high-disturbance driver system is verified by the SiC battery test and simulation equipment which is researched independently. In addition, an anti-interference driver circuit and driver line based on the actual engineering requirements are designed to decrease the CM interference and DM interference. Finally, the high anti-interference driver system for SiC power modules was verified by experiment.

Dead time compensation in H-bridge inverters

This paper presents the procedure to apply compensation for the distortion created by the dead time/blanking time in H-bridge inverters, as those used in grid-connected photovoltaic (PV) inverters. It also deals with the selection of an appropriate value of dead time, by measuring the turn-on and turn-off times of the switching devices. Dead time/blanking time is needed in H-bridge inverters to prevent 'shoot through' or cross-conduction current through the inverter leg due to the non-ideal nature of the switching devices. The distortion effect of the dead time is analysed by practical experimentation, showing the importance of selecting the most appropriate value of dead time. This is then followed by a procedure to apply compensation to decrease the distortion and thus decrease harmonics caused by the dead time. Both simulation and experimental results will be presented. Testing was carried out on a grid-connected PV inverter which was designed and constructed for this research.

Analysis of the novel Snapback-Free LIGBT with fast-switching and improved latch-up immunity by TCAD Simulation

In this letter, a novel snapback-free LIGBT with fast-switching and improved latch-up immunity is proposed and investigated by TCAD simulation. The structure features a shorted-anode NPN (SA NPN) beside the insulated oxide trench in the N-buffer and a lowly doped P-region (PD) alongside the deep-oxide trench (DOT) in the N-drift. The SA NPN provides an effective path of electron extraction and completely suppresses the snapback voltage. The PD changes the transmission path of hole current, makes the distribution of hole current more uniform, and contributes to the depletion of the drift region. As simulation results show, at the same forward voltage drop of 1.40 V, the turn-off time for the proposed SAPD LIGBT is reduced by 36.6% and 57.4%, respectively, compared with SA LIGBT and DOT LIGBT. In addition, compared with DOT LIGBT, breakdown voltage is increased by 7.6% and latch-up voltage is increased by nearly 20% for the proposed SAPD LIGBT.

Cryogenic power electronics at megawatt-scale using a new type of press-pack IGBT

Electrical characteristics of a press-pack IGBT stack have been investigated experimentally in both static and dynamic tests at room temperature and at 77 K in an effort to identify a megawatt-scale class semiconductor that performs well electrically, thermally, and mechanically. It has been observed that the forward voltage drop and the turn-off time are both noticeably reduced at cryogenic temperatures, suggesting significant improvement in the device operating area. Furthermore, the stack was subjected to repeated thermal cycles between room temperature and 77 K without observing any degradation. A circuit simulation of a 200-kW boost converter based on the characterized press-back IGBT stack exhibited a reduction in switching and conduction losses at 77 K by 60% and 24%, respectively compared to the values at room temperature. It is expected that the type of press-pack IGBT stacks tested will be key elements to build high power dense, megawatt-scale cryogenic converters for future all-electric ships and electric airplanes.

Model-Based Dead Time Optimization for Voltage-Source Converters Utilizing Silicon Carbide Semiconductors

Dead time significantly affects the reliability, power quality, and efficiency of voltage-source converters. For silicon carbide (SiC) devices, considering the high sensitivity of turn-off time to the operating conditions (> 5× difference between light load and full load) and characteristics of inductive loads (> 2× difference between motor load and inductor), as well as large additional energy loss induced by the freewheeling diode conduction during the superfluous dead time (∼15% of the switching loss), then the traditional fixed dead time setting becomes inappropriate. This paper introduces an approach to adaptively regulate the dead time considering the current operating condition and load characteristics via synthesizing online monitored turn-off switching parameters in the microcontroller with an embedded preset optimization model. Based on a buck converter built with 1200-V SiC MOSFETs, the experimental results show that the proposed method is able to ensure reliability and reduce power loss by 12% at full load and 18.2% at light load (8% of the full load in this case study).

Structural and optical properties of vanadium pentoxide nano-thin films with different thickness

ABSTRACTVanadium pentoxide nano-thin films were deposited on JGS infrared quartz substrates by radio frequency (R.F.) reactive magnetron sputtering at different sputtering times. The effects of thickness on the surface structural and optical properties of the films were studied systematically. X-ray diffraction (XRD) results show that all the prepared nano-films are polycrystalline vanadium pentoxide films (V2O5) on (001) preferred orientation. The Root-Mean-Square (RMS) roughness decreases from 2.8 nm to 1.2 nm with the increase of thickness. Optical properties were measured by an optical-testing setup. The results indicate that both the optical turn-off time and turn-on time diminish with the reduction of the film thickness, which cover from 2.1 ms and 39 ms at 447 nm to the minimum of 1.5 ms and 27 ms at 154 nm respectively. Additionally, the dynamic range of transmittance varies greatly from 3.16 at 154 nm to the maximum of 5.89 at 447 nm under a laser beam of 1064 nm.

Fast Turn-Off Switching of Vertically-Aligned Negative Liquid Crystals by Fine Patterning of Pixel Electrodes

We investigated the two-dimensional (2D) confinement effect on the switching of vertically-aligned negative liquid crystals (LCs) by an electric field applied between the top and bottom patterned electrodes. When an electric field is applied to a patterned vertical alignment (PVA) cell, virtual walls form in the middle of the gaps between and at the center of the patterned electrodes. These virtual walls formed in a PVA cell results in the turn-off time being dependent on the pitch of the patterned electrodes as well as the cell gap. We found that a short response time can be achieved by the fine patterning of pixel electrodes with little decrease in the transmittance. The obtained numerical results agree well with the model based on the 2D confinement effect of LCs.

Low Loss Insulated Gate Bipolar Transistor With Electron Injection (EI-IGBT)

A new type insulated gate bipolar transistor (IGBT) with electron injection (EI-IGBT) is proposed in which an N+-buried layer is implemented in P-base region. The mechanism of the EI-IGBT is that electrons are injected in both OFF- and ON-state, thus accelerated electron–hole recombination is achieved, resulting in a fast turn-off process. Meanwhile, a low forward voltage drop is obtained due to an enhanced conductivity modulation. The simulation results show that, compared with the conventional IGBT, the proposed EI-IGBT delivers a comparable breakdown voltage while featuring an 80% shorter turn-off time (or a 72% lower turn-off loss) or a 23% lower forward voltage drop, resulting in a reduction of total energy loss.

Enhanced Performances of a Photocatalytic Reactor for Wastewater Treatment Using Controlled Modulation of Leds Light

One of the main limitations related to the industrial utilization of a photocatalytic process is the use of UV lamps that have several disadvantages such as the low quantum efficiency (QE). One of the approaches to increase the QE consists in the use of controlled periodic illumination (CPI). In this regard, Light Emitting Diodes (LEDs) are the best choice as light sources, since they can be electronically controlled by using LED dimming techniques, allowing variable turn-on and turn-off times on a microsecond time-scale. The aim of this work is to investigate the influence of controlled modulation of LEDs light on the performances of a photocatalytic reactor for wastewater treatment using TiO2 immobilized on glass spheres (TiO2/GS). The experiments were realized with a pyrex cylindrical batch photoreactor irradiated by three power UV-LEDs and placed surrounding the external body of the cylindrical photoreactor. The system adopted for the controlled modulation of LEDs light is composed by a photovoltaic panel (PV), a dc–dc converter dedicated to the maximum power point tracking of the PV panel and a dc–dc converter dedicated to drive the UV LEDs. A system controller is also included, whose goal is to ensure matching between the maximum available PV power, the LED power and the resulting low-frequency LEDs dimming modulation. The experimental results showed that the use of certain types of duty-cycle dimming modulation waveforms, including periodic and non-periodic waveforms and combinations of them, have been discovered to improve the photo-catalytic reactor performances. In particular, the use of a modulation of LEDs dimming like sinusoidal and pseudo-sinusoidal waveforms is more effective than the fixed dimming. The best results in terms of methylene blue degradation (about 25% in less than 1 h) have been achieved with a pseudo- sinusoidal waveform.