Positive DC Voltage Research Articles

Surface charge characteristics in a three-electrode surface dielectric barrier discharge

The surface charge characteristics in a three-electrode surface dielectric barrier discharge (SDBD) are experimentally investigated based on the Pockels effect of an electro-optical crystal. The actuator is based on the most commonly used SDBD structure for airflow control, with an exposed electrode supplied with sinusoidal AC high voltage, a grounded encapsulated electrode and an additional exposed electrode downstream supplied with DC voltage. The ionic wind velocity and thrust can be significantly improved by increasing DC voltage although the plasma discharge characteristics are virtually unaffected. It is found that the negative charges generated by the discharge of the three-electrode structure accumulate on the dielectric surface significantly further downstream in an AC period compared to the actuator with a two-electrode structure. The negative charges in the downstream region increase as the DC voltage increases. In addition, the DC voltage affects the time required for the positive charge filaments to decay. The positive DC voltage expands the ionic acceleration zone downstream to produce a greater EHD force. The amplitude of the DC voltage affects the electric field on the dielectric surface and is therefore a key factor in the formation of the EHD force. Further research on the surface charge characteristics of a three-electrode structure has been conducted using a pulse power to drive the discharge, and the same conclusions are drawn. This work demonstrates a link between surface charge characteristics and EHD performance of a three-electrode SDBD actuator.

Studies on a novel microporous electrospun poly(vinyl alcohol)‐based polymer electrolyte membranes for high‐performance battery applications

AbstractINTRODUCTIONSolid polymer blend electrolytes are scientifically interesting promising materials as electrolytes in advanced solid state electrochemical devices applications such as batteries, electrochemical display devices, smart windows, etc. The solid polymer blend electrolyte has several advantages including high energy density, a solvent free condition, structural stability, light weight, leak proof, good electrode electrolyte contact, ease of fabrication, easy processability and good mechanical properties.OBJECTIVESThe present research work deals with the study of composition and conductivity behavior of polymer blend electrolyte complex membranes based on PVA and PVP complexed with different weight percent KClO4 salt, prepared by electrospinning technique. The resultant polymer blend electrolytes have been characterized by XRD, FTIR and AC conductivity studies.METHODSPorous PVA based nanofiber membranes were prepared using a typical electrospinning technique with a horizontal arrangement. A stainless steel needle (24 G, outer diameter: 0.50 mm, inner diameter: 0.35 mm) was connected to an electrode of a high voltage power supply (Spellman, model CZE1000R) which could generate positive DC voltages up to 30 kV and a grounded stainless steel plate was placed at 10 cm distance from the needle tip to collect the nanofiber membranes.RESULTS AND DISCUSSIONA novel electrospun polymer electrolyte membranes comprising a blend of poly (vinyl alcohol) (PVA) and poly (vinyl pyrrolidone) (PVP) containing various concentrations of potassium perchlorate KClO4 salt are prepared using electrospinning technique. The structure and complexation of the polymer electrolyte membranes have been confirmed from X‐ray diffraction (XRD) and Fourier transform infrared (FTIR) spectral studies. The ac conductivity studies are performed to measure the ionic conductivity of the polymer electrolyte complex systems in the temperature range 298‐353 K and it is also found that the temperature dependence ionic conductivity data seems to follows the Arrhenius relation. The influence of complex membranes composition on the ionic conductivity has been discussed. The maximum ionic conductivity value is obtained to be 9.1×10−4 S cm−1 at 298 K for PVA‐PVP‐KClO4 (50‐35‐15) polymer system with 15 wt.% KClO4 salt. Scanning electron microscopy studies have been performed and reported.CONCLUSIONSFree standing, flexible complex polymer electrolyte membranes based on various compositions of PVA‐PVP‐KClO4 have been prepared. The presence of amorphous regions due to complexation of polymer salt matrices has been confirmed from XRD and FTIR analysis. The maximum value of ionic conductivity has been obtained to be 9.1 × 10−4 S cm−1 at 298 K for PVA‐PVP‐KClO4 (50‐35‐15) complex polymer electrolyte system with 15 wt.% KClO4. The excellent performance, such as high values of ionic conductivity, of polymer blend electrolyte membranes suggest that the membranes can be used as the best candidate for high performance solid state batteries.

Characterization of DC corona discharge current pulses using high-frequency measurement techniques

This paper presents corona discharge current pulse characterization under positive and negative DC voltage excitations. Two electrode systems with three different gap spacings generated corona discharges. Different corona modes in atmospheric air were observed with voltage level changes. Commercial shunt resistors and a high-frequency current transformer (HFCT) captured corona current pulses. The appropriate resistor type and value were determined for the shunt resistor measurement. BNC terminator was proposed as a shunt resistor to detect corona discharge current pulses, and the availability of the shunt resistors and HFCTs for corona pulse detection was discussed. After gathering corona discharge pulse data, features from the pulses were extracted. The best features describing corona discharge types were specified using a recursive feature elimination method based on a decision tree estimator. The corona discharges were discriminated with an accuracy rate of 0.994.

A Performance Optimized CSTBT with Low Switching Loss.

A novel Performance Optimized Carrier Stored Trench Gate Bipolar Transistor (CSTBT) with Low Switching Loss has been proposed. By applying a positive DC voltage to the shield gate, the carrier storage effect is enhanced, the hole blocking capability is improved and the conduction loss is reduced. The DC biased shield gate naturally forms inverse conduction channel to speed up turn-on period. Excess holes are conducted away from the device through the hole path to reduce turn-off loss (Eoff). In addition, other parameters including ON-state voltage (Von), blocking characteristic and short circuit performance are also improved. Simulation results demonstrate that our device exhibits a 35.1% and 35.9% decrease in Eoff and turn-on loss (Eon), respectively, in comparison with the conventional shield CSTBT (Con-SGCSTBT). Additionally, our device achieves a short-circuit duration time that is 2.48 times longer. In high-frequency switching applications, device power loss can be reduced by 35%. It should be noted that the additional DC voltage bias is equivalent to the output voltage of the driving circuit, enabling an effective and feasible approach towards high-performance power electronics applications.

Interplay between electron and ion plasma waves

We report the observation of the interplay between the first kind of high-frequency electron-dominated plasma waves (EPWs) and the second kind of low-frequency ion-dominated plasma waves (IPWs) in a DC glow discharge plasma experiment. On application of positive DC voltage on a probe immersed in plasma when the drift velocity of the electrons (vd) ≈1.3× the thermal velocity of electrons (vte), it gives rise to an instability resulting in the formation of double layers (DL). Under DL conditions, the anode sheath extends deep into plasma. The DL represents a nonequilibrium plasma condition that is known for the instabilities and excitation of plasma waves. In this experiment, the effect of the monotonic increase of plasma density fluctuations (δn≈0.01%) on the evolution of DL has been studied. The interplay between EPWs and IPWs is observed in the course of this investigation. The overall plasma response on density fluctuations is recorded as floating potential fluctuations (FPFs) which vary with an increase of δn. The FPFs exhibit order-chaos-order transition with the evolution of DLs. Further analysis of the fluctuations using the wavelet method gives a spectrum in both the time and frequency domains simultaneously. Wavelet spectra reveal that the nonlinear evolution of FPFs is a consequence of the interplay between EPWs and IPWs due to the trapping and detrapping of electrons in the extended anode sheath region. These results explain that the ordered oscillation corresponds to dominant EPWs and the chaotic fluctuations are due to the coexistence of EPWs and IPWs. This new understanding may assist to study the complex plasma behaviour observed in laboratories as well as space plasmas.

Study on Development Characteristics of Partial Discharge in Oil-Pressboard Insulation under Constant DC Voltage

The converter transformer is the core equipment of HVDC transmission system, the valve-side winding of which needs to withstand DC voltage. Partial discharge is one of the main threats to the safe operation of converter transformer, yet the characteristics of partial discharge development of the oil-pressboard insulations under constant DC voltage are insufficiently understood. In order to better understand the partial discharge characteristics of the oil-pressboard insulation under DC voltage and provide deeper theoretical support for insulation diagnosis of converter transformers, development characteristics including the time-varying tendency of discharge magnitude and repetition rate of partial discharge in oil-pressboard insulation under constant positive and negative DC voltage were studied. The results indicate that the development of partial discharge in a needle-plane oil-pressboard insulation model under constant DC voltage has three stages: the intensive discharging stage, the silent-burst stage, and the breakdown stage. Throughout all stages, the partial discharge magnitude and repetition rate first decrease and increase afterwards. At the silent-burst stage, the partial discharge appears in the form of a “cluster” with very large magnitude and repetition rate. Each cluster exists for tens of seconds but with at a very long interval with each other. Further analysis shows that the repeated accumulation and dissipation of free charges on the surface of the pressboard cause the above phenomena. Negative charges are easy to accumulate and difficult to dissipate under the same voltage amplitude compared to positive charges, leading to a weaker actual electric field at the needle tip and thus partial discharges under negative DC voltage with a lower magnitude and longer interval.

Design of 6 GHz Variable-Gain Low-Noise Amplifier Using Adaptive Bias Circuit for Radar Receiver Front End

This paper presents a variable-gain low-noise amplifier (VGLNA) based on an adaptive bias (ADB) circuit for the radar receiver front end. The ADB circuit processes the signal separated by a coupler at the LNA output port. First, the ADB circuit rectifies the coupled signal into positive DC voltage through a rectifier, which is then inverted to control a junction-gate field-effect transistor (JFET). The voltage-controlled current of JFET flows through a voltage-divider network and finally produces the DC biasing voltage for the BJT base termination, which decreases with the increase in the input RF power. The proposed VGLNA operates automatically in high gain at low input power and low gain at high input power, providing a wider dynamic range as compared to the constant-bias counterpart. For validation, a prototype is fabricated and measured at 6 GHz. As observed, the base biasing voltage generated by the ADB circuit is changed from 858 mV to 798 mV as the input power increases from −50 dBm to 0 dBm. As a result, the dynamic range represented by the input P1dB point (IP1dB) has an increase of 6.5 dB, while LNA still maintains a high gain of 15.15 dB at low input power.

Study on Space Charge Characteristics in XLPE Under DC Voltage Superimposed by Impulse Voltage

In direct current (dc) transmission lines, power cables are susceptible to the invasion of switching overvoltage or lightning overvoltage. This causes the accumulation of space charge in the insulation due to the higher transient composite electric stress. Space charge is an important factor in dielectric breakdown, especially under high electric stress. However, until now, there are few reports on space charge characteristics under the composite stresses of dc voltage and impulse voltage. In this article, a modified pulsed electroacoustic space charge measurement system used for dc voltage superimposed by impulse voltage is developed by reasonably choosing resistor and capacitor elements in the measuring system. Then, space charge characteristics in cross-linked polyethylene (XLPE) are measured under dc voltage, impulse voltage, and dc voltage superimposed by impulse voltage. The test results show that hetero-charges dominated in the XLPE bulk under a positive dc voltage, whereas homo-charge injection occurred from the semiconductor (SC) electrode under a negative dc voltage. However, a continuous impulse voltage with high amplitude can cause a large degree of homo-charge injection from both electrodes. Moreover, greater homo-charge injection appeared under the negative impulse voltage than that under the positive impulse voltage. Under a dc voltage superimposed by an impulse voltage, the superposition of voltages with the same polarities facilitated homo-charges injection from both electrodes to a greater extent than did the superposition of voltages with opposite polarities. Furthermore, regardless of the polarity of the applied dc voltage, greater space charge accumulation appeared in XLPE when a negative impulse voltage is superimposed.

SF6 decomposition behaviour under partial discharge of typical insulation defects in gas‐solid insulated valve‐side bushing of converter transformer

AbstractIn this paper we investigated SF6 decomposition behaviour of typical insulation defects in gas‐solid insulated converter transformer valve‐side bushing under partial discharge (PD). Additionally, we compared the results with that of gas insulated switchgear (GIS). The results indicated that SF6 decomposition behaviour varies with the insulation defects type. For metal protrusion defects, the proportion ranking of CO2 and SO2 can be related to whether the needle tip is wrapped with epoxy resin‐impregnated paper (ERIP). The proportion of carbon‐containing products is much higher under contamination defect than under other defects. Moreover, the proportion of carbon‐containing components is higher under flashover condition than under PD condition and is accompanied by the appearance of H2S and CS2. However, the yield of SO2F2 is always low. Compared to negative DC voltages, positive DC voltages have a higher proportion of carbon‐containing components, mainly in the form of more CO2 and less SOF2. Compared to the PD decomposition behaviour of typical insulation defects in GIS, when PD involves ERIP, the proportion of carbon‐containing products, especially CO2, is significant higher, while the proportion of sulphur containing products, especially SO2F2, is lower.

Ionic wind velocity and energy efficiency improvement in needle-net ionic wind generator by electrical field optimization

Ionic wind produced by high voltage discharge has been proved as a promising technique in heat dissipation, food drying, electrostatic precipitation and air propulsion. On the other hand, the low wind velocity and the low energy efficiency of the ionic wind generators limit their performance in practical industrial applications. To improve this, a single needle-net electrode structure ionic wind generator driven by positive DC voltage is constructed and the effects of the applied voltage and electrode structure on the discharge characteristics and the converting efficiency from electric energy to kinetic energy have been investigated. The results show that with the increase of the applied voltage from 4 kV to 11 kV, the discharge shows four stages, burst pulse, streamer corona, glow corona and spark discharge, and the wind velocity increases monotonously and reach 1.90 m/s at 11 kV. At the same applied voltage, the shorter needle-net distance leads to the larger wind velocity. At 15 mm needle-net distance, the needle-net electrode structure ionic wind generator shows a maximum energy efficiency value of 2.19%. A metal circular plate is attached on the needle electrode to change the spatial electric field distribution, increase the field intensity of the discharge gap, and promote the particle collision. It is found that the wind velocity and energy efficiency can be improved from 1.90 m/s to 2.35 m/s, and 1.87% to 3.14%, at same applied voltage and needle-net distance. The cooling experiment shows that the ionic wind generator with metal circular plate needle-net electrode has better heat dissipation effect.

Influence of positive DC electric field on rime icing on the insulator and its experimental verification in the natural environment

AbstractThe electric field imposes a significant effect on ice accretion on the insulator. The impact of an AC electric field on insulator icing in an artificial climate chamber has been addressed. Compared with AC, DC electric field exerts an attraction on supercooled water droplets, which is more detrimental to the power system. Moreover, the icing on energised insulators is rarely studied in the natural environment. In the present research, an electrical, fluid coupled‐field simulation was carried out on the insulator. The force characteristics and motion deviation features of water droplets at different positive DC electric field strengths were studied. On this basis, rime icing on the insulator energised with different positive DC voltages was investigated in the field. Results show that the charged droplet shifts along the electric field line under a positive DC voltage. The deviation degree of the droplet increases with the increment of the voltage and droplet size and decreases with an increase in wind speed. As the voltage rises, the surface roughness, icing amount and icing length of rime ice‐covered insulator increase. Consequently, compared with that without energisation, the local collision coefficient, icing amount and icing length increase by 17.6%, 46.4% and 63.9%, respectively, under a 40 kV DC voltage.

(Digital Presentation) Degradation and Recovery of Low Temperature Poly-Si Thin Film Transistors Under DC and AC Bias Stresses

The low temperature poly-Si thin-film transistors (LTPS TFTs) have been extensively applied in the AMLCD and AMOLED due to their high carrier’s mobility and driving currents, and the ability to integrate the driving circuits onto the same substrate. The main mechanisms causing the degradation of the LTPS TFTs under bias stress are: hot carrier effect and self-heating effect. In this study, the degradation and recovery phenomena of the LTPS TFTs stressed by the hot carrier effect conditions would be systematically investigated. The device structures used in this study are n-channel LTPS TFTs with different lengths of lightly doped drain (LDD).First, we simultaneously apply a small positive DC voltage, approximately the threshold voltage plus 1V (Vth+1= +3 V), to the gate terminal and a large positive DC voltage (+12 V) to the drain terminal of the LTPS TFTs with three different LDD’s lengths. These stressing conditions would cause the TFTs operated in the saturation region, so that the channel is pinched off. And the electrons would be accelerated by a large transverse electric field when they drift from the source terminal to the drain one. The energetic electrons would impact the lattices of the channel and the interface between the gate dielectric and the channel near the drain terminal, causing the defect states and electron-hole pair generation. Few of the carriers with enough energy to overcome the energy barrier of gate dielectric would be trapped by the defects in it. The hot carrier effect causes the degradation of the TFTs devices, including the decrease of ON current and carrier mobility and the increase of OFF current, but less degradation of the threshold voltage and subthreshold swing. After the bias stressing, the resting time is added to investigate the recovery phenomena. The difference in the amount of degradation and the location of defects would cause the different recovery ratio. After the end of bias stressing, all of the terminals are not applied with any voltages in the resting periods. The electrons and holes generated in the channel near the drain terminal would recombine, and the defect states generated by the hot carrier impact slightly reduce, which causes the recovery phenomena of the degraded transistors.Then, we apply a small AC voltage (0 ~ +3 V) to the gate terminal and a large positive DC voltage (+12 V) to the drain one at the same time. This mode of bias stressing conditions is closer to the real operating mode of the TFTs in the driving circuits. From the experimental data, it could be found that there is no significant difference in the degradation of the TFTs under different frequency of AC signals applied on the gate. But the recovery ratio tends to gradually increase as the frequency increasing.Finally, a small positive DC voltage (+3 V) is applied to the gate terminal, and a large AC voltage (0 ~ +12 V) to the drain one at the same time. From the experimental data, it could be found that with the increase of AC signal frequency, the degradation of the TFTs decreases, but the recovery ratio of the TFTs increases due to the reduction of the effective stressing time in one period. As compared to the results of all stressing conditions, the TFTs, both of the gate and drain terminals applied with DC voltages, exhibit the largest degradation ratio but the least recovery one. However, the TFTs, as the gate terminal applied with DC voltages and drain one with AC voltage, exhibit the less degradation ratio but the largest recovery one.

(Digital Presentation) CeOx Capping for Ferroelectric Y:HfO2 Films

In recent years, HfO2 has been paid a lot of attention as a ferroelectric material due to its excellent scalability and complementary-metal-oxide-semiconductor (CMOS) process compatibility [1]. Some of the issues of ferroelectric HfO2 are wake-up and fatigue effect, increase and decrease of remanent polarization (P r) along with switching cycles, and low endurance. Generally, these phenomena are understood as a result of the increase and redistribution of oxygen vacancies (VO) in HfO2 films [2]. By the way, it is reported that CeOx can release and absorb oxygen from adjacent oxides [3]. In this study, we propose the stacking structure of CeOx and ferroelectric HfO2 to improve endurance and investigate electric properties and voltage application sequence to suppress the fatigue effect.5 mol% Y-doped HfO2 (Y:HfO2) and CeOx capping layers of metal-ferroelectric-metal (MFM) capacitors were deposited by atomic-layer-deposition (ALD) with W bottom and top electrodes by sputtering. Post metallization annealing (PMA) was performed at 450 and 500oC for the various duration. Figure 1 shows hysteresis loops of the capacitors with and without CeOx capping annealed at 450oC for 20 minutes. Large hysteresis on CeOx capping is observed even same annealing temperature and duration. Enhancement of transformation to ferroelectric phase can be explained as tensile stress to Y:HfO2 due to the difference of coefficient of thermal expansion (CTE) between CeOx and Y:HfO2. Variation of switching polarization (P SW), the difference between positive and negative P r, as a function of the number of switching cycles is also investigated and shown in figure 2. Both capacitors are annealed at 500oC for 100 minutes to crystallize. In the case of without CeOx capping, continuous wake-up effect and breakdown over 3×107 times switching are observed. On the other hand, the capacitor with CeOx capping shows a slight wake-up effect and fatigue after 106 times switching, additionally, endurance is improved to 3×109 times switching. The reason why fatigue and prolonging endurance occur is suspected that oxygen ions in the CeOx layer pin polarization domains and compensate VO in Y:HfO2. To suppress fatigue, we propose the recovery process by positive DC voltage application to top electrodes. In figure 3, hysteresis loops of the capacitor with CeOx capping before and after recovery voltage application. One can observe the larger hysteresis after recovery.This work was supported by JST-COI (JPMJCE1309). One of the authors, Kazuto Mizutani, was supported by The FUTABA Foundation.[1] T. S. Boscke, et al., Appl. Phys. Lett., 99, 102903 (2011). [2] M. Pesic, et al., Adv. Funct. Mater., 26, pp. 4601–4612 (2016). [3] M. Mamatrishat, et al., Vacuum, 86, pp. 1513-1513 (2012). Figure 1

A Dual-Buck-Boost DC–DC/AC Universal Converter

This paper proposes a universal converter that is capable of operating in three modes for generating positive dc voltage, negative dc voltage, and sinusoidal ac voltage. By controlling the duty-cycle of two half-bridges, an inductor is operated at a high frequency to control the voltage across two film capacitors that constitute a dual-buck-boost converter. Two additional half-bridges operating at a fixed state or line frequency are used to select the mode of operation. Compared to the latest universal converter in the recent literature, the proposed topology has the same switch count while reducing the number of conducting switches for inductor current and reducing the number of switches operating at high frequency. The operation of the proposed dual-buck-boost dc–dc/ac universal converter is analyzed. Experimental results are presented for validation. The power conversion efficiency of the 100 W experimental prototype modeled in PLECS is approximately 98%.

Influence of trace SF 6 on streamer corona development in SF 6 /N 2 mixtures under positive DC voltages

Influence of trace SF ₆ on streamer corona development in SF ₆ /N ₂ mixtures under positive DC voltages

Degradation characteristics of insulation near aluminium foil edges inside dry‐type bushing cores under electrothermal compound stress

Insulation breakdown of dry-type valve-side bushing cores under electrothermal compound stress has become a key factor limiting the safe and stable operation of the converter transformer. Based on slices of the real bushing core, it is observed for the first time that fold, peeling off, and fracture defects exist near the aluminium (Al) foil edge, accompanied by many metal spikes with a curvature radius <4 μm. Coupled with a capacitor screen thickness of ∼2 mm, an electrical tree model is designed to simulate insulation defects near aluminium foil edges inside dry-type bushing cores, whose insulation degradation characteristics under electrothermal compound stress are investigated accordingly. The results show that high temperature significantly increases the dielectric loss heat energy density and Joule heat energy density, accelerating the insulation degradation near Al foil edges. The parallel crepe paper interface significantly accelerates the growth of electrical trees under AC-superimposed positive DC voltage, while this effect is not significant under AC voltage. As the crepe paper consists of wooden fibres of 10 μm diameter, the electrical trees tend to grow along interfaces between fibres and epoxy resin to form “feathery” electrical trees in epoxy resin-impregnated paper samples.

The Effects of Pulse Shape on the Selectivity and Production Rate in Non-oxidative Coupling of Methane by a Micro-DBD Reactor

The conversion of methane to ethylene has been investigated in a micro-DBD reactor with electrodes containing charge injector parts and excited with a negatively nano-second pulse voltage superimposed on a positive dc voltage. The effect of changing the characteristics of pulsed voltage such as pulse rise time (5–7 ns), total pulse width (12–14 ns), and pulse fall time (5–7 ns) on generation rate and products selectivity of the methane plasma has been studied. The kinetic model includes twenty species (electron, ions, radicals, and neutrals). The results showed that change in input pulse shape changes the generation rate and selectivity of neutral products. The rate of voltage change during pulse on-time significantly changed the instant C2H4 selectivity. With increasing the pulse rise and fall times the ethylene selectivity decreases, while the hydrogen selectivity increases. Results also showed that the electron reactions are dominant conversion channels during pulse on-time, while they had lower contributions in conversion progress during pulse off-time and the conversion process during this period is mainly governed by the radical reactions.

The Effect of DC Voltage Pre-Stress on the Breakdown Voltage of Air under Composite DC and LI Voltage and Test Circuit: Design and Application

The use of HVDC systems is increasing in number due to technological innovations, increasing power capacity and increasing customer demand. The characteristics of insulation systems under composite DC and LI voltage must be examined and clarified. In this study, firstly, experimental circuits were designed to generate and measure composite DC and LI high voltage using a simulation program. The coupling elements used were chosen according to simulation results. Afterward, experimental circuits were established in the laboratory according to the simulation results of the designed experimental circuit. Then, breakdown voltages under composite DC and LI voltage for less uniform and non-uniform electric fields were measured with four different electrode systems for positive and negative DC voltage pre-stresses with different amplitudes. The 50% breakdown voltage was calculated using the least-squares method. Finally, 3D models were created for the electrode systems used in the experiments using the finite element method. The efficiency factors of electrode systems calculated with the FEM results were correlated with the experimental breakdown voltage results. Thus, the breakdown behavior of air under bipolar and unipolar composite voltages (CV) was investigated. In conclusion, the experimental results showed that very fast polarity change in bipolar CV causes higher electrical stress compared to unipolar CV.

Buck–Boost Common Ground Bridgeless PFC (CGBPFC) Rectifies With Positive/Negative Output

This article proposes new common ground bridgeless power factor correction rectifiers suitable for use in any application which requires a positive or negative dc power supply. The main advantage of the proposed rectifiers, compared to previous works, is the provision of the common ground between input and output, which eliminates electromagnetic interference (EMI) associated with high rates of change of voltage and consequently reduces the need for EMI common mode filtering. The converter also provides step-down and step-up operation, and facilitates positive or negative output voltages with a low number of semiconductor devices operating simultaneously. High power factor, acceptable grid-side current quality, and high efficiency are also achieved. Two variants are presented, referred to as type-I and type-II, which offer common ground positive and negative dc voltages, respectively. Closed-loop control of the converters is provided by a dead-beat current controller in the inner loop. Experimental results are presented for a 500-W prototype, operating from 220 and 110 Vrms input to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 48 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 200 Vdc output. The experimental results demonstrate the capability for step-down and step-up ac-to-dc power conversion with a peak efficiency of 96.8% and 96.6% in the positive and the negative outputs, respectively.

Investigation on Electrical, Thermal, and Mechanical Properties of Silicone Rubber ATH Nanocomposites

In the present study, investigations have been carried out by choosing the nano-sized ATH (30 – 50 nm) particles as filler content in silicone rubber to acquire a deep insight to understand the use of nano ATH fillers in silicone rubber on its performance, to use it as insulation structure as an outdoor insulator. Variation in the surface condition of silicone rubber nanocomposites due to corona aging and the recovery characteristics analysis carried out through contact angle measurement. Nano ATH added in silicone rubber, up to 3 wt% of filler, shows increased dielectric constant with less loss factor. Water droplet-initiated discharges on silicone rubber nano ATH composites under DC voltage measured using UHF technique and the damage caused zone analyzed through AFM studies and by surface potential measurement, which indicates higher surface roughness and increased charge trap depth. It is observed that negative DC voltage has higher CIV followed by positive DC and AC voltage. Laser Induced breakdown studies (LIBS) show a direct correlation between plasma temperature and material surface hardness. Also, on laser shining on the surface of the specimen, its temperature was measured on the backside of the specimen through thermal imaging confirming increased diffusivity of temperature. Laser flash analysis shows a direct correlation between filler content in base polymer and thermal conductivity and diffusivity. Higher storage modulus and activation energies measured from the dynamic mechanical analysis indicate the significance of prepared composites as an excellent mechanical support structure for the power system network.