Average Voltage Value Research Articles

Assessment of 2H–SiC based intercalation compound for use as anode in lithium ion batteries

The improvement in electrode materials to upgrade lithium ion battery (LIB) is at heart of research related to energy devices. Herein, we report on the prospects of using 2H–SiC as an anode material in LIB on the basis of first principles based theoretical predictions. The energy profiling of high symmetry structural sites pointed out that the site TC related to tetrahedral configuration with carbon is favorable intercalation site in the host. The reaction of Li with stoichiometric as well as non-stoichiometric 2H–SiC are found endothermic which points to their unsuitability for lithiation process in LIBs. However, Li intercalation into the host in presence of Si monovacancy appeared an exothermic process which motivated us to study this system in detail. The Li atom after intercalation into the host is found ionized thereby donating its 2s electron to carbon atoms. The average value of the lithium insertion voltage and theoretical capacity are calculated as 1.87 V and 85 mA h/g respectively for the host simulated in the form of supercell LixSi15C16. The diffusion barrier faced by lithium atom while moving along crystalline a-axis is minimum (among all the paths considered here) when it follows a path that links hexagonal rings while passing carbon atoms. On the other hand, in case of motion along c-axis, similar results are found for minimum energy path that is along Tc site. The low diffusion barrier will facilitate the lithium ion to move quickly that points to fast charging capability of the battery.

Simulasi Pemodelan Sistem Eksitasi Statis pada Generator Sinkron terhadap Perubahan Beban

Excitation system is one of the most important parts of synchronous generators, where the system functions to provide dc power to the field generator coil. Iin this study, a static excitation system consisting of transformers and connected thyristors in bridge configuration has been implemented in synchronous machines that operate as 206,1 mva capacity generators, 16,5 kv using the help of matlab simulink r2017b software. By adjusting the load given to the generator, variations in excitation currents can affect the amount of output voltage generated by the generator so that it can increase and decrease the induced voltage. In full load conditions, namely p = 175 mw, q = 100 mvar, the results of the study show that when the simulation is run at alpha 0 °, it is known that the average value of dc voltage is 496,4 v, excitation current is 1057 a and voltage generator output has increased beyond its nominal voltage of 16,72 kv. in this case, to maintain the terminal voltage, the excitation current must be reduced by increasing the angle of shooting of the thyristor to an alpha angle of 45 °, so that the average dc voltage can be reduced to 479,3 v, as well as the excitation current to 985,9 a. the generator output voltage at the alpha 45 ° angle is obtained according to its nominal value of 1,.5 kv.

Design of Smart Nurse Call (Caller Nurse) Based on Android

The limited number of nurses is a problem that often occurs in the world of health which has an impact on the high workload of nurses resulting in less optimal patient care and decreased patient satisfaction. According to Institute for Healthcare Improvement, nurses spend only 20-30% of their time in direct patient care, the rest on documentation and administration processes. So, hospitals generally provide nurse calls so families don't have to leave patients to find nurses.The purpose of this study was to make it easier for patients to use Smart Nurse Call, especially for patients with acute diagnosis conditions and it's easier for nurses to monitor patient's condition. It's also examines the distance of data transmission in one building to determine the performance of wireless (access points).Based on data from test results, the quality of data transmission using wireless media is known that access point has data transmission limit. In testing distance at AH building stated that data transmission based on the range on the 1st floor is able to reach the entire corridor, for 2nd floor it can reach a distance of 13 meters while on 3rd floor it cannot be reached. The data from suitability test of smart nurse call tool showed that the suitability level of the device was quite high and almost same as manual test at 97.65%. The data from stress test results from push button get average voltage value low position at 0 V and average high voltage at 4.675 V.

Analysis of Power Transformer Insulation: A Case Study in 150 kV Bantul Substation

Insulation of the transformer is one of the essential components. So that the quality of the resistance in the isolation of the transformer is essential to note the condition, in order to find out the condition of the transformer isolation, several tests must be performed, namely the polarization index, delta tangent, and break down voltage. In this study, all three tests were carried out on Transformer 1 in the 150 kV Bantul substation. Polarization index testing itself is testing the leakage current on the transformer isolation by comparing the test results for 1 minute with the results of the 10-minute drive test. While delta tangent is testing capacitive leakage current in the isolation transformer, and break down voltage is a test of the ability of the breakdown voltage in transformer insulation oil. Based on the results of the analysis, it can be seen that the value of the transformer polarization index in 2016 and 2018, the average value between the windings has been in the rating of 1.25-2.0. As for the delta tangent test results in 2016 and 2018, the value between the capacitive parts is already in the rating of 0.18% -0.36%. For the breakdown voltage test results in 2016 and 2018, the average breakdown voltage value is 43.9 kV/mm - 65.5 kV/mm. From these data, it can be concluded that the transformer isolation conditions in 2016 and 2018 are in good condition, although there was a decline in the transformer isolation conditions in 2016. However, the National Electric Company has made repairs and maintenance of the isolation transformer. This is seen due to an increase in the quality of transformer insulation in 2018. Repair and maintenance of transformer insulation are done to maximize the work system and the life of the transformer.

First-principles study of monolayer SnS2(1−x)Se2x alloys as anode materials for lithium ion batteries

Based on density functional theory, the performance of the monolayer SnS2(1−x)Se2x alloys with variation of x = 0, 0.25, 0.5, 0.75, 1 as the anode material for using in Lithium-ion batteries (LIBs) are examined. Numerical results show that the values of the band gap of SnS2(1−x)Se2x alloys decrease with the increase of Se concentration. For Li adsorption, the alloys changed from semiconductor to metal after the insertion of Li and becomes suitable for being used as electrode material. Also, the low barrier energy is kept and the adsorption strength is enhanced in the SnS2(1−x)Se2x alloys compared with that of the pristine SnS2 system. With increased concentration of Se, little influence on the average open circuit voltage (OCV) value is observed, though the capacity of the system decreases from 293 to 194 mAh/g.

Mitigation of Current Distortion in a Three-Phase Microinverter With Phase Skipping Using a Synchronous Sampling DC-Link Voltage Control

To improve light load efficiency, a three-phase photovoltaic (PV)-based microinverter may operate in single-phase, two-phase or three-phase mode depending on the available input power. Therefore, its dc-link capacitor may be subjected to large peak-to-peak voltage ripple when operating in phase skipping mode. This paper determines the minimum value of the dc-link capacitor by allowing the maximum acceptable voltage ripple on the dc link. This allows for the use of film capacitors instead of electrolytic capacitors in order to improve the microinverter reliability. Unfortunately, higher dc-link voltage ripple introduces harmonic distortion on the inverter output current waveform if it is not compensated for by the dc-link voltage controller. This paper proposes a simple synchronous control method to regulate the dc-link voltage with the presence of large voltage ripple. The dc-link voltage controller is synchronized with the phase-locked loop and samples the average value of dc-link voltage without introducing unwanted harmonics into the voltage sense path. Experimental results were obtained from a 300-W three-phase half-bridge microinverter prototype to verify the proposed dc-link voltage control performance. Inverter output current total harmonic distortion of 1.6% was achieved even though the dc-link peak-to-peak voltage ripple reached as high as 87 V with 219-V split dc-link voltage. Dynamic response is fast enough to easily track the most extreme ramp change in input PV power.

Influence of pulse waveform on machining accuracy in electrochemical machining

Low machining accuracy has been a technical bottleneck for the application and promotion of electrochemical machining (ECM). Since the 1990s, it has been recognized by scholars that high-frequency pulsed power supply can improve the precision of ECM. But, in terms of the experimental results of our study, a new discovery was found that the increasing of the frequency has no effect on improving the machining accuracy of ECM. Comparing with the DC power supply, the experiment results show that the machining accuracy under pulsed power supply is decided by effective average voltage value, regardless of the frequency of the pulsed waveform, the duty cycle, and the pulse peak.

An Improved PWM Strategy for Z-Source Inverter With Maximum Boost Capability and Minimum Switching Frequency

Z-source inverter provides a competitive single-stage dc–ac power conversion with the capability of both buck and boost voltage regulation. In order to maximize voltage gain and to increase efficiency, this paper proposes an improved pulse-width modulation (PWM) strategy. By adjusting the shoot-through duty ratio of one-phase leg, it regulates the average value of intermediate dc-link voltage, which is the same as the instantaneous maximum of three-phase line voltage in one switching time period $(T_{s})$ . And the other two-phase legs maintain the fixed switching states. Thus, the equivalent switching frequency of power devices in the inverter bridge is reduced to $1/ 3f_{s}$ ( $f_{s}$ is the frequency corresponding to $T_{s}$ ). The operating principles and closed-loop controller design are analyzed and verified by simulation and experiments. Compared with the existing PWM strategies, the improved PWM (IPWM) strategy demonstrates higher efficiency under full operation range of low voltage gain (1.27-2) application. However, with the IPWM strategy, the inductor current and capacitor voltage contain six-time-line-frequency ripples, which consequently require large size of the passive components when the output frequency is very low. Thus, it is also suitable for 400–800-Hz medium frequency aircraft and vessel power supply system due to a relatively high output line frequency. Furthermore, the idea of IPWM strategy can be extended to other kinds of three-phase impedance network-based inverters.

Performance of Zn/Graphite rechargeable cells with 1-ethyl-3-methylimidazolium trifluoromethanesulfonate based gel polymer electrolyte

There is an urgent need to fulfill the global thirst for energy in an efficient and safer way. Since long ago, Li based devices have been employed to cover up the high rising energy demand in the society. But, upon the realization of the hazardous nature and the cost of Li, a substantial attention has been focused on exploiting ecofriendly and naturally abundant materials to be employed for fabricating devices such as rechargeable cells, fuel cells, solar cells and super capacitors. Main aim of this study is to design a low cost, environmental friendly, rechargeable cell. Hence, attempts have been taken to use non Li based electrodes and a gel polymer electrolyte (GPE) with no solvents. The cell consists with natural graphite and Zn electrodes and an ionic liquid (IL) based GPE. ILs are the most recently introduced substitute for solvents in GPEs which possess some attractive features. For the preparation of the GPE, poly(vinylidinefluoride-co-hexafluoropropylene) (PVdF-co-HFP), zinc trifluoromethanesulfonate (Zn(CF3SO3)2 and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (1E3MITF) were used as the polymer, the salt and the ionic liquid (IL) respectively. Configuration of the fabricated cell was Zn/IL based GPE/graphite. Cells had an average open circuit voltage (OCV) value of 1.10 V. Variation of OCV with time was quite low. Cells were characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) as well as continuous galvanostatic charge discharge (GCD) test. Properties of the bulk electrolyte as well as electrode/electrolyte interface were rather stable. Average specific charge was remaining around 4 mAhg–1. Discharge capacity was varying around 2 mAhg–1. These results reflect the possibility of using this cell for applications with some further modifications to increase the performance.

DPWM techniques in digitally controlled, EMI compliant DC-DC converters

This paper aims to present a combined, DPWM based control method and spectrum flattening technique of a mid-power range DC-DC converter. The research goal was to obtain sustainable results in both switching control and EMI compliance, using one 8 or 16 bits RISC MCU as main control unit running a performance- and speed-optimized firmware. This approach describes a hybrid method preserving the good dynamic performances of an analog switching regulator controller and adding the flexibility of controlling the output voltage by adjusting the duty cycle value of a DPWM signal and thus controlling the average voltage value of the signal applied in the feedback circuit of a DC-DC converter. Beside the feedback control of the DC-DC converter an active EMI reduction technique applies on this design by taking advantage on the constant-frequency, forced-continuous current mode architecture of the switching regulator controller, which allows its frequency to be synchronized with an external control clock dithered by a software implemented pseudo-random sequence generator. All this efforts concludes in reducing the noise power considerably at the main peak and at the next peaks.

Potential and Electric Field Characteristics of Broken Porcelain Insulator

<span lang="EN-GB">Overhead line insulators can be damaged for various reasons during their service life. Porcelain or glass insulators once damaged can affect the reliability of power system networks. This paper presents the study of voltage and electric characteristics along the surface of a broken porcelain insulator located in a string of 10 unit insulators. Three models of broken porcelain insulators were being proposed and the analysis results on voltage and electric characteristics were individually collected. The broken porcelain insulator with the most significant effect were then being investigated in the strings of 10 unit insulators. The finite element software of Quickfield was used to analyze the voltage and electric characteristics. Form the presented results, it is proven that the single porcelain insulators with broken shed at the nearest to the electrode terminal gave the most significant effect of voltage and electric field distribution pattern along the creepage distance. However, when this type of broken insulator was included in a string of 10 unit insulators, maximum average value of voltage achieved once the broken insulator was located at the HV terminal. Meanwhile, the highest electric field strength was recorded when the broken insulator was located in the middle of the string.</span>

Effect of Excess PbI2 in Fully Printable Carbon‐based Perovskite Solar Cells

AbstractExcess lead iodide (PbI2) has been reported to improve the power conversion efficiency (PCE) in the standard perovskite solar cell (PSC) with 2,2,7,7‐Tetrakis(N,N‐di‐p‐methoxyphenyl‐amine)‐9,9‐ spirobifluorene (spiro‐OMeTAD) as a hole‐transporting material. In this study, we studied the effect of having excess PbI2 in fully printable carbon‐based perovskite solar cells (PSC). Excess amounts of PbI2, ranging from 0 % to 15 %, were added to the equimolar perovskite solution for infiltration in the carbon‐based PSC architecture. There was an improvement in the average value of open‐circuit voltage (0.87 to 0.91 V) with increased PbI2, but there was no clear trend in fill factor and current density. All devices showed good stability under ambient conditions without encapsulation. The device containing 15 % excess PbI2 showed degradation under continuous illumination, whereas there was no degradation with an equimolar ratio of perovskite precursors.

Containment and Consensus-Based Distributed Coordination Control to Achieve Bounded Voltage and Precise Reactive Power Sharing in Islanded AC Microgrids

This paper presents a novel distributed approach to achieve both bounded voltage and accurate reactive power sharing regulation in ac microgrid. The coupling/trade-off effects between bus voltages and reactive power sharing regulation are first analyzed in detail to provide a guideline for coordinated control design. Furthermore, a containment and consensus-based distributed coordination controller is proposed, by which the bus voltage magnitudes can be bounded within a reasonable range, instead of only controlling average voltage value. Furthermore, the accurate reactive power sharing between distributed generators can be achieved simultaneously. Then, a detailed small-signal model is developed to analyze the stability of the system and the sensitivity of different parameters. Experimental results are presented and compared, where the controller performance, robust performance under communication failure, and plug-and-play operation are successfully verified.

A Novel Remaining Useful Life Prediction Approach for Superbuck Converter Circuits Based on Modified Grey Wolf Optimizer-Support Vector Regression

The reliability of power packs is very important for the performance of electronic equipment and ensuring the reliability of power electronic circuits is especially vital for equipment security. An alteration in the converter component parameter can lead to the decline of the power supply quality. In order to effectively prevent failure and estimate the remaining useful life (RUL) of superbuck converters, a circuit failure prognostics framework is proposed in this paper. We employ the average value and ripple value of circuit output voltage as a feature set to calculate the Mahalanobis distance (MD) in order to reflect the health status of the circuit. Time varying MD sets form the circuit state time series. According to the working condition time series that have been obtained, we can predict the later situation with support vector regression (SVR). SVR has been improved by a modified grey wolf optimizer (MGWO) algorithm before estimating the RUL. This is the first attempt to apply the modified version of the grey wolf optimizer (GWO) to circuit prognostics and system health management (PHM). Subsequently, benchmark functions have been used to validate the performance of the MGWO. Finally, the simulation results of comparative experiments demonstrate that MGWO-SVR can predict the RUL of circuits with smaller error and higher prediction precision.

Maximum Boost Control of Diode-Assisted Buck–Boost Voltage-Source Inverter With Minimum Switching Frequency

Diode-assisted buck–boost voltage-source inverter achieves high voltage gain by introducing a switch-capacitor based high step-up dc–dc circuit between the dc source and inverter bridge. As for the unique structure, various pulse width modulation (PWM) strategies are developed with regard to the chopped intermediate dc-link voltage. In order to maximize voltage gain and increase efficiency, this paper proposes a novel PWM strategy. It regulates the average value of intermediate dc-link voltage in one switching time period ( $T_{s}$ ) the same as the instantaneous maximum value of three-phase line voltage by controlling the front boost circuit. Then, the equivalent switching frequency of power devices in the inverter bridge can be reduced to $1/3f_{s} (f_{s} = 1/T_{s})$ . The operating principle and closed-loop controller design are analyzed and verified by simulations and experiments. Compared with existing PWM strategies, the new control strategy demonstrates less power device requirement and higher efficiency in high voltage gain applications. It is a more competitive topology for wide range dc/ac voltage regulation in renewable energy applications. Furthermore, with new control strategy, the dc-side inductor current and capacitor voltage contains six-time line-frequency ripples. To overcome the undesired influence of low frequency ripples, it is also suitable for 400–800 Hz medium frequency aircraft and vessel power supply system.

Top-gate organic field-effect transistors fabricated on paper with high operational stability

We report on top-gate organic field-effect transistors (OFETs) fabricated on specialty paper, PowerCoat™ HD 230 from Arjowiggins Creative Papers coated with a buffer layer composed of a polyvinyl alcohol (PVA) and polyvinylpyrrolidine (PVP) blend. OFETs operate at low voltages and display average carrier mobility values of 1.7 ± 1.1 × 10−1 cm2/Vs, average threshold voltage values of −1.4 ± 0.2 V, and average on/off current ratio of 105. OFETs also display excellent operational stability demonstrated by stable 1000 scans of the transfer characteristics and by stable on-currents displaying less than 6% change during a DC bias stress test at VDS = VGS = −10 V for 1 h. Furthermore, OFETs on paper display a decrease of only 7% in their on-state current during a bending test. The performance of these OFETs on paper is comparable to that displayed by top-gate OFETs with the same geometry fabricated on glass substrates.

DC voltage control strategy of chain star STATCOM with second‐order harmonic suppression

Chain static synchronous compensators (STATCOMs) with star structure produce second-order harmonic fluctuations on the DC side. This effect is often ignored and only the average voltage value is taken into consideration when describing this system for control purpose. In this study, the unbalance of per-phase DC voltages caused by active power absorbed and consumed by the chain is analysed. The steady-state expressions regarding the average capacitor voltage balancing between phase clusters as well as the suppression of second-order harmonic fluctuation are obtained, respectively, based on the injection of fundamental and third-order harmonic zero-sequence voltages. Although the expressions are helpful to understand the essence of DC capacitor voltage control, this method has complicated calculation process and the calculation results may be beyond the modulation limit. Therefore, it is not conducive in real-time control. For this reason, a new control strategy based on the instantaneous zero-sequence voltage injection is proposed. The evaluation function with the transient variables is established to get the instantaneous value of the zero-sequence voltage including fundamental and third-order harmonic components. The fundamental and third-order harmonic zero-sequence voltages are automatically allocated to fully use the remaining modulation capacity. Finally, simulation and experimental results are provided, which verifies the correctness of the theoretical analysis and the high performance of the proposed method.

The Surface Polarized Graphene Oxide Quantum Dot Films for Flexible Nanogenerators.

Abundant disorderly-distributed surface functional groups, such as hydroxyl, carboxyl, ether and amino groups, endow an isolated graphene oxide quantum dot (GOQD) the polar property due to the symmetry breaking, although the aggregated counterparts present no polarization owing to the random orientation. Here, flexible polarized films were fabricated using aggregated GOQDs with the assistance of external electric fields and their polarization was confirmed with the electrostatic force microscopy and polarization-electric field hysteresis loop. Such polarized GOQD films may induce charges under externally applied deformation. Here, we fabricated nanogenerators based on the films, which gave out an average current value of 0.12 μA and an average voltage value of 12 V under a mechanical force of 60 N. This work has proposed a convenient electric-field-assisted method to give the nanomaterials new functions, which can be generalized to other materials and found applications in various fields.

A Pulse Voltage Application in Electrochemical Reduction of Solid CaWO4 Powder

Among more than thirty known tungsten containing minerals, only scheelite (CaWO4) and wolframite ((Fe, Mn)WO4) are industrially important [1]. Scheelite is the most abundant mineral of tungsten, but wolframite is used more than scheelite due to easier dissolution in alkaline solutions used in present processing methods [2]. An alternative method based on electrochemical reduction of CaWO4by direct current applications in molten salt solutions was recently reported [3-5]. In this study, pulse voltage and constant voltage reduction mechanisms were compared and an optimization of reduction kinetics was achieved. Studies have shown that faster reduction rates could be achieved during pulse voltage applications compared to constant voltage applications, when average voltage value of pulse voltage application was the same as its constant counterpart. Furthermore, analysis of charge, energy and theoretical reduction graphs showed that reduction of calcium tungstate occurs at higher potential differences than 2.2 V, between calcium tungstate and graphite.

세라믹막을 이용한 미생물연료전지의 전기화학적 특성 연구

단일챔버 미생물연료전지에 분리막으로 세라믹막과 나피온막을 적용하여 전기발생특성을 분석함으로써 세라믹막의 적용가능성을 구명하고자 하였다. 또한 환원전극으로서 백금촉매가 도포된 탄소천과 일반 탄소천을 사용하여 백금촉매 효과 및 전기발생특성을 비교하였다. 회분식 실험에서 전기발생특성이 가장 안정적인 것은 acetate를 기질로 사용하였을 때였다. Formate는 전기발생특성이 acetate보다 다소 높았으나 불안정하였고 propionate와 butyrate는 acetate에 비하여 전기발생량이 상대적으로 낮았다. 환원전극으로서 백금촉매가 도포되어 있는 탄소천과 일반 탄소천을 비교한 결과 백금촉매가 도포된 탄소천의 전력발생량이 일반 탄소천에 비하여 1.2배 높게 나타났지만 약 5배 정도 비용 차이가 있음을 고려하면 미생물연료전지의 적용에 있어 효율성과 경제성은 함께 고려되어야 할 것으로 판단된다. 분리막으로서 세라믹막과 나피온막을 적용한 미생물 연료전지에서 발생한 평균 전압은 합성폐수를 이용한 실험에서 각각 <TEX>$523.67mV{\pm}49.41mV$</TEX>, <TEX>$424.09mV{\pm}79.95mV$</TEX>이었다. 미생물연료전지에 분리막으로 세라믹막과 나피온막을 적용하여 전력발생 및 유기물제거효율을 비교한 결과, 세라믹막이 나피온막의 대안이 될 수 있음을 확인하였다. This study attempts to verify the applicability of ceramic membrane as a separator by comparing the power generation characteristics in single-chamber MFCs using ceramic membranes to those in the MFCs using nafion membrane. The generated power in MFCs by using acetate as a substrate was more stable than that by using formate, propionate and butyrate, respectively. It was shown that the generated power by using formate substrate in MFCs was unstable and a little higher than that by using acetate, and the power generated by using propionate and butyrate were lower than that by using acetate. In order to find out the Pt catalyst effect, it was compared the power generated in MFCs using Pt-coated carbon cloth as electrode to that power using normal carbon cloth. The power generated in MFCs using Pt-coated carbon cloth as electrode was 1.2 times higher than that using normal carbon cloth. The Pt-coated carbon cloth was about 5 times more expensive than normal carbon cloth. It is suggested that both power generation efficiency and cost together should be considered in selecting electrodes of MFCs. It was found that the ceramic membrane was superior to nafion membrane by comparing to the power generation characteristics obtained. It was shown that average voltage values were <TEX>$523.67mV{\pm}49.41mV$</TEX> by using synthetic wastewater, in MFCs of ceramic membrane as a separator. While average voltage values were <TEX>$424.09mV{\pm}79.95mV$</TEX> by using synthetic wastewater, in MFCs of nafion membrane as a separator. The organic removal efficiency, 41.7% by using ceramic membrane was a little bit higher than 40.8% by using nafion membrane. This research implies ceramic membrane can be a valid alternative to nafion membrane as a separator when considering the power generation and the efficiency of organics removal.