Safe Voltage Research Articles

Capacitor Voltage Balancing Control for a Novel 5-Level Dual Active Bridge Converter

Multilevel technology is an attractive solution to increase the cost effectiveness and power density of dc solid state transformers. In this article, a novel five-level (5L) dual active bridge (DAB) converter topology is proposed. By stacking two neutral-point-clamped (NPC) converters at the primary side, the proposed topology could quadruple the input dc-bus voltage of a conventional two-level (2L) DAB converter. Besides, by analyzing the working principle of the 5L-DAB converter, a voltage balancing control method is carried out. With the aid of the voltage balancing method, voltages of the four series-connected dc-bus capacitors in the 5L-DAB converter can be actively balanced, guaranteeing safe operation voltage for all the semiconductor switches. After that, the operation range of the proposed voltage balancing method is derived by theoretical analysis. Finally, the performance of the proposed converter topology and voltage balancing method have been verified by experimental results.

Sosialisasi Peralatan Kelistrikan dan Pengambilan Keterangan untuk Mengungkapkan Sebuah Kasus di Kepolisian Resort Pidie Sebagai Ahli Elektro

Electricity is very useful for human life. However, if an error in use results in a danger to the safety of humans, livestock and property. Sometimes electricity is also used for special purposes for which there are no guidelines, this will be very risky to safety. As in the case that occurred recently in the Pidie Resort Police area, the Head of the Pidie Resort Police assigned his members for the benefit of the police service in the context of the task of carrying out an examination of electrical experts to obtain information regarding the discovery of a body in the mountain river of Gampong Lhok Broh, Meureudu District, District Pidie Jaya. The expected objectives of this activity are; So that participants can understand the benefits of electrical energy and the basic principles, operation, and maintenance of electrical equipment, Provide participants with knowledge (in general) about how to work and maintain electrical equipment that may be designed and used in a community environment, Demonstrate directly the dangers of some related electrical equipment cases currently being handled by the police. This activity was carried out from October 1 to November 30 2019 and consisted of 3 stages namely; Preparation, Execution, and Compilation of Reports. Based on inspections and field trials in two places, the following conclusions can be drawn; Electric current is dangerous for the human body depending on the amount of current and duration. The effect of electric current on humans starts with tingling/numbness to effect the heart which can cause death. Water is a conductor that can carry electric current properly. The safe voltage limit for humans is 50 Volt AC assuming the human body is 1000 Ohm resistant, the safe current limit for humans is 30 mA. The dedicated team also as electrical experts discusses scientific about matters related to electrical hazards and their effects on the human body.

ANALISIS ELECTRIC GROUNDING SYSTEM UNTUK KEANDALAN DAN KESELAMATAN DALAM INSTALASI KELISTRIKAN

Electrical installations need to be installed correctly by referring to the basic guidelines, namely the General Guidelines for Electrical Installation (PUIL) for the country of Indonesia, or referring to other guidelines with international standards, namely the International Electrotechnical Commission (IEC) and IEEE. Electrical installations must have a protection system, high reliability when operating, and the ability to respond to installation disturbances quickly. The protection system provides safety for living things, property, and the electrical installation itself. The grounding system is one of the protections to maintain the reliability of the installation and protect the safety of personnel, the grounding system serves to ensure a stable and safe power supply voltage. This study discusses the grounding system, namely grounding resistance (GR), and its relation to the grounding rod material and soil resistivity (SR). The writing of the paper used a qualitative descriptive method, the basic supporting material was carried out with a literature review and references to previous research. The assessment of the two components aims to produce a good grounding system with economical design and maintenance costs, it is stated that the grounding rod material and soil resistivity are important factors for the grounding installation system.

Axial Flux Permanent Magnet Synchronous Generators for Pico Hydropower Application: A Parametrical Study

A pico hydropower plant is an energy harvesting system that allows energy production using the power of the water flowing in small watercourses, and in water distribution network. Axial Flow Flux Permanent Magnet Synchronous Generator (AFPMSG) are particularly suitable for this application, being efficient machines that achieve high power with small dimensions. This paper presents a parametrical study of several configurations and topologies of three-phase and single-phase AFPMSG, for pico hydropower application, to assess the most suitable dimensional characteristics for the most energy production using a safe voltage of 25 V. The AFPMSGs here considered has a simple single stator and rotor configuration, commercial-type permanent magnets, and concentric windings, to facilitate their cost-effective construction and the spread of their use also in developing countries. For each AFPMSG considered, the power output was calculated using 3-D modelling and Finite Element Analysis; besides, the different parameters and features that affect the power output were evaluated at different rotational speeds. The results achieving a power density up to 100 W/cm3, at 1000 rpm with energy produced to 1.7 kWh/day.

Effect of Disorder and Doping on Electronic Structure and Diffusion Properties of Li3V2O5

V2O5 in its ω phase (Li3V2O5) with excess lithium is a potential alternative to the graphite anode for lithium-ion batteries at low temperature and fast charging conditions owing to its safer voltage (0.6 V vs Li+/Li(s)) and high lithium transport rate. In-operando cationic disorder, as observed in most ordered materials, can produce significant changes in charge compensation mechanisms, anionic activity, lithium diffusion, and operational voltages. In this work, we report the variation in structural distortion, electronic structure, and migration barrier accompanied by disorder using first-principles calculations. Owing to the segregation of lithium atoms in the disordered state, we observe greater distortion, emergence of metallic behavior, and potential anionic activity from nonbonding oxygen states near the Fermi level. Redox capacity can be tuned by doping with 3d metals, which can adjust the participating cationic states, and by fluorine substitution, which can stabilize or suppress anionic states. Moreover, the suppression of anionic activity is found to decrease structural distortion, which is crucial for mitigating voltage fade and hysteresis. Diffusion barrier calculations in the presence of disorder indicate the activation of the remaining 3D paths for lithium hopping which are unavailable in the ordered configuration, explaining its fast-charging ability observed in experiments.

Effects of thiol‐ene click reaction on morphology and electro‐optical properties of polyhedral oligomeric silsesquioxane nanostructure‐based polymer dispersed liquid crystal film

AbstractPolymer dispersed liquid crystals (PDLCs) have lit a flash of interest due to the distinctive property of electrically controlled switching. However, too high‐driving voltage associated with porous polymer networks always limit their wider range of applications. Herein, we reported a PDLC system containing LCs, 2,2′‐(Ethylenedioxy)diethanethiol (DET) with thiol groups, cage‐like nanostructure acrylic polyhedral oligomeric silsesquioxane (KH570‐POSS) and KH570‐SiO2 nanoparticle modified by acrylic groups. The cage‐like KH570‐POSS microstructure was injected to the polymer matrix when KH570‐POSS reacted with DET via thiol‐ene click reaction. The morphological results demonstrated that the droplet size increased with the higher content of DET due to the decrease of the crosslink between the acrylic groups in KH570‐POSS, which results in a less dense of polymer network and thus make the LC droplets easier to be driven in the electric filed. Then, a silica‐based nanoparticle KH570‐SiO2 modified by acrylic groups was introduced into the system. The results indicated that KH570‐SiO2 could replace partial KH570‐POSS to form the polymer network via thiol‐ene click reaction, which increased the compatible ability of SiO2 nanoparticles in the as‐made film. The contrast ratio was increased to 165 when there was nearly 5 wt% content of KH570‐SiO2. Besides, the driving voltage was reduced by almost 60% and the sample could be fully driven by 30 V which is lower than the safe voltage (36 V). This study opens a route for the preparation of commercial PDLC films by thiol‐ene click reaction, enabling the creation of low‐voltage‐driven smart windows.

High‐performance electric heating yarns based on graphene‐coated cotton fibers

AbstractGraphene and graphene‐based materials can emit far‐infrared light with a wavelength of 6–14 μm that are beneficial to the human body when subjected low voltage, which have attracted much attention. However, the most previously reported heating devices based on graphene materials are thin films; therefore, there are a series of problems such as poor air permeability, difficulty in integration with clothing, and uncomfortable wearing. In this work, a simple ultrasonic dip‐coating method is used to prepare the electric heating yarns based on graphene‐coated cotton fibers, where the high‐performance hybrid yarns can be driven at a safe voltage. The number of ultrasonic dip‐coating and the linear density of the yarns have shown the great influence on electric heating performance. After three ultrasonic dip‐coatings, the temperature of the hybrid yarn with 3.5 mm diameter and 10 cm length can reach ~70°C at a voltage of 20 V, while the heating power is only ~2.5 W. Our studies have demonstrated the potential of hybrid yarns which can be used in the field of heating clothing or medical care.

Nanotomographic observation and statistical analysis of overcharging induced cracks in LiCoO2 single crystalline particles

Particle fracture represents an important mode of battery electrode degradation. Extensive cracking occurs in the layered oxide cathodes of lithium-ion rechargeable batteries when they are charged beyond safe operational voltages. In this paper, we analyze the morphology and distribution of cracks in over 100 overcharged LiCoO2 (LCO) single-crystalline particles imaged via X-ray nanotomography. We observe a strong particle size dependence in both nucleation and growth of cracks, with percentage of cracked particles, crack size, and crack surface area per unit volume all increasing significantly with particle volume. Increasing the cutoff voltage above 4.6V is found to trigger much more pronounced crack growth, which we attribute to the large misfit stress caused by the H1-3 to O1 phase transition. This study offers valuable statistical insights into the fracture behavior of layered oxide cathodes and reveals the importance of particle size control on electromechanical degradation of battery electrodes.

Model-based degradation prediction on impedance data and artificial neural network for high-temperature polymer electrolyte membrane fuel cells after hydrogen starvation

Degradation caused by H2 starvation is a typical reason for a limited lifetime in high-temperature polymer electrolyte membrane fuel cells (HT-PEM FC). Here, a long short-term memory (LSTM) artificial neural network (ANN), trained on experimental electrochemical data from a long-term H2 starvation/regeneration routine, was used to predict the effect of H2 starvation.In a first application, different voltage decreases were simulated, which FCs typically exhibit during starvation/regeneration routines. The results of three simulation scenarios (3, 5 and 10 mV decrease per regeneration step) showed that critical resistances appeared at output voltages of 0.51, 0.49 and 0.48 V, respectively (compared to the reference voltage of 0.6 V).In a second application, the same FC was virtually set to continue to operate normally (i.e., under regeneration conditions) at certain degrees of starvation, after which voltage was virtually kept constant at 0.48, 0.50 and 0.51 V. For 0.48 and 0.50 V, all simulated resistances fluctuated critically, which corresponded well to experimental data. However, for 0.51 V all simulated resistances never reached critical values. Hence, a safe operational voltage range between 0.6 and 0.51 V is suggested for stable continued FC cycling, which would prevent the occurrence of more severe (irreversible) degradation.

An effective and cleaner discharge method of spent lithium batteries

The rapid development of new energy vehicles has exponentially increased the output of spent lithium-ion batteries (LIBs). The extraction and recovery of valuable metals from spent LIBs are expected to alleviate the shortage of battery materials. However, the spent LIBs to be recycled may still have certain amount of usable output power. If the battery is disassembled and crushed directly, the residual electricity may be hazardous. Therefore, discharge pretreatment should be carried out before disassembling and crushing spent LIBs. To date, electrochemical discharge in conducting solutions has been widely investigated and applied to discharge pretreatment, but there is no convincing evidence of its effectiveness. At the same time, non-electrochemical discharge in conducting powders has been investigated as a possible cleaner and more effective discharge method. Therefore, our current article reports the results of a series of experiments performed with spent LIBs to explore electrochemical discharge in conducting solutions and non-electrochemical discharge in conducting powders. We also systematically discuss the advantages and disadvantages of different discharge media in terms of their discharge efficiency, the potential existence of solid/liquid/gas phase contaminants, and their effectiveness. The experimental results obtained showed that battery discharge reached the safe voltage of 2 V and that the voltage rebound behavior occurs after 48 h standing. This is called the voltage relaxation phenomenon in an electrical field, which could cause certain safety risks during battery disassembly and crushing. Therefore, the effect of voltage rebound was also studied, and the obtained results showed that the voltage was over-discharged after flake-graphite discharge, which would cause irreversible damage to the anode material of the batteries and lead to battery failure. This is of great significance for the discharge pretreatment of spent LIBs. Therefore, flake-graphite discharge is an cleaner and effective discharge method for spent LIBs.

Highly Dispersed Antimony-Bismuth Alloy Encapsulated in Carbon Nanofibers for Ultrastable K-Ion Batteries.

Antimony-based alloys have appealed to an ever-increasing interest for potassium ion storage due to their high theoretical capacity and safe voltage. However, sluggish kinetics and the large radius of K+ lead to limited rate performance and severe capacity fading. In this Letter, highly dispersed antimony-bismuth alloy nanoparticles confined in carbon fibers are fabricated through an electrospinning technology followed by heat treatment. The BiSb nanoparticles are uniformly confined into the carbon fibers, which facilitate rapid electron transport and inhibit the volume change during cycling owing to the synergistic effect of the BiSb alloy and carbon confinement engineering. Furthermore, the effect of a potassium bis(fluorosulfonyl)imide (KFSI) electrolyte with different concentrations has been investigated. Theoretical calculation demonstrates that the incorporation of Bi metal is favorable for potassium adsorption. The combination of delicate nanofiber morphology and electrolyte chemistry endows the fiber composite with an improved reversible capacity of 274.4 mAh g-1, promising rate capability, and cycling stability upon 500 cycles.

Electrocution Risk of Capacitive Discharge Shocks: Application to Electric Vehicle Charging.

It is difficult to electrocute (induce ventricular fibrillation) with capacitive discharge shocks. With small capacitance values, the high voltages required for the necessary charge are rarely seen in industrial situations (e.g. electric vehicle charging stations). On the other hand, with large capacitance values, the discharge time is so great that the shock couples inefficiently with the cardiac cells. The update to IEC 60479-2 sets the C1 "mostly-safe" charge limit of 3 mC for a short "impulse function" pulse. We calculated the equivalent capacitor stored charge for an arbitrary capacitance value using the simple single membrane time constant model for the cardiac response. The peak membrane response was set equal to that of the 3 mC impulse function response to calculate the safe values for stored charge, voltage, and energy. The total stored charge, per se, cannot be used simplistically to estimate the danger of a capacitive discharge shock. A capacitive-discharge shock cannot be accurately compared to a rectangular shock with a duration equal to the shock time constant. The greater the capacitance, the larger the fraction of wasted charge in coupling to the heart and thus the shorter equivalent duration compared to the shock time constant. For a capacitive discharge shock this translates to a stored charge of 3 mC increasing up to 9 mC for a 10 capacitor using the assumed 575 load for an electric-vehicle (EV) charging station. In the area of interest for 1 - 10 the safe voltage ranges from 1300 to 4700 V, which includes the 1500-VDCscope of EV charger standard IEC 61851-23. For C > 100 the voltage asymptote is 700 V.

Sn-, Sb- and Bi-Based Anodes for Potassium Ion Battery.

Owing to the abundant resources of potassium resources, potassium ion batteries (PIBs) hold great potential in various energy storage devices. However, the poor lifespan of PIBs anodes limit their merchant applications. The exploitation of anode materials with high performance is one of the critical factors to the development of PIBs. Metallic Sn-, Sb-, and Bi-based materials, show promising future thanks to their high theoretical capacities and safe working voltage. However, the rapid capacity decay caused by the large K+ is still a pivotal challenge. In this review, recent progresses on alloying anodes were summarized. Schemes, such as ultra-small nanoparticles, hetero-element doping, and electrolyte optimization are effective strategies to improve their electrochemical properties. This review provides an outlook on the nanostructures and their synthesis methods for the alloying-type materials, and will stimulate their intensive study for practical application in the near future.

The regulation of electro-optical properties of the polymer dispersed liquid crystal films doped ZnO whiskers under applied pre-orientation voltage

ABSTRACT This study demonstrates a simple and effective method for the fabrication of PDLC films with low driving voltage by applying a pre-orientation voltage during the photoinitiated polymerisation process. The results indicated that the electro-optical performances of PDLC films have been regulated successfully with the pre-orientation voltage method, in which the voltage could pre-orient the LC molecules and change the interface between the LC molecules and the polymer matrix. By manipulating the proportion of liquid crystal and polymer monomers and introducing ZnO whiskers as the dopant, the driving voltage was dramatically reduced and the sample could be fully driven by an electric field with a voltage of 32 V below the safe voltage. The results indicated that the polymer meshes were broadened by the addition of ZnO whiskers due to their excellent UV-absorbing properties that result in a slower polymerisation rate, while the contrast ratio could maintain a good value of 31. It has been found that both application of pre-orientation voltage and doped ZnO whiskers can optimise the electro-optical performance of the PDLC and reduce the driving voltage. Therefore, this experiment is expected to provide certain research value to fabricate the low-driven PDLC films for practical applications.

Low Resistance Hot-Spot Diagnosis and Suppression of Photovoltaic Module Based on I-U Characteristic Analysis

In the hot-spot fault of photovoltaic modules, there is a low resistance hot-spot fault caused by crystal defects, such as internal crack and PN junction failure. When the faulty area is partially shaded, it will produce severe temperature rise, accelerate the aging of battery unit, and even cause fire, which will affect the safe operation of the photovoltaic system. In this paper, the low resistance hot-spot fault endangering the safe operation of photovoltaic modules is taken as the research object; the shunt effect of equivalent low resistance caused by crystal defects under local shadow occlusion is explained by using the reverse characteristic of PN junctions of battery units, and its failure mechanism is analyzed. The three working states of the power generation system and the formation conditions of hot-spots in the process of power generation are analyzed in detail. By building a simulation model, the heating power distribution characteristics of hot-spots under different external local shadow occlusions are simulated, and finally, the fault characteristics and the fault diagnosis criterion of low resistance hot-spots are obtained. A control algorithm for low resistance hot-spot diagnosis and suppression based on I-U characteristic analysis is designed, and verified by simulation and experiment. The experimental results show that the control algorithm proposed in this paper can use the I-U characteristics of photovoltaic modules to determine whether there is a low resistance hot-spot fault, and carry out real-time control according to the judgment results. If it is judged that a low resistance hot-spot module is partially shaded, actively fixing the working point of the system near the safe voltage will protect the safety of the photovoltaic module. Otherwise, performing global MPPT will ensure the maximum power output of the system.

Multichannel pulse high-current driver of magnetic actuator

Magnetic linear actuators have a wide range of applications. Their main advantage is the ease with which they can be controlled by regulating the current. However, high electrical power is required for obtaining a large continuous force, acceleration, and stroke from a device with small dimensions. In this study, we developed a comprehensive open-source system consisting of simple movable iron magnetic actuators, a four-channel controller, and dedicated software. The graphical user interface facilitates the designing of the sequence of piston strokes, including the start time, duration of movement, and force for each stroke separately. The controller generates a high current of pulses, which allows achieving a high force, acceleration, and stroke from small-sized coils while maintaining a relatively safe voltage. The system was originally designed as a reagent syringe driver to control the rapid mixing process used for studying the kinetics of enzymatic reactions. However, this driver may also be applied in various other scientific as well as nonscientific applications.

Synergistic flame retardant weft-knitted alginate/viscose fabrics with MXene coating for multifunctional wearable heaters

Flexible wearable heaters have received increasing attention in energy-saving, diverse personal thermal requirements, and healthcare management. Herein, considering the fire safety application of wearable heaters, the biodegradable alginate fibers and flame retardant (FR) viscose fibers are attempted to mix and weft-knit into the fabric, which interestingly exhibits synergetic flame retardancy with low afterflame time, afterglow time, and peak heat release rate. Further, assisted by the highly conductive Ti3C2Tx (MXene) nanosheets on the surface of the fabric and the periodic nested loops of the knitted fabric, the integrated fabrics possess excellent electrical performance (2Ω sq−1) with the MXene content of 9.13 wt%, electromagnetic interference (EMI) shielding efficiency of 55 dB in the X band, preferable Joule heating performance under safe low voltage (123 °C at 3.5 V) and sunlight/far-infrared heating performance. The superior flame retardancy and multifunctional properties arose from the high-temperature induced well-constructed char layer, unique functionality of interconnected MXene network and multiple scattering of light or wave. Combined with the superior flame retardancy and multifunctional properties, the weft-knitted alginate/FR viscose fabrics with MXene coating become the ideal candidate materials in the fields of wearable heaters with high safety.

Silk-Waste-Derived Porous Carbon for Fast Electric Heating under Safe Voltage

Fast and safe electric heating is highly needed in extreme climates or thermal therapy. Herein, porous activated carbon derived from silk waste is prepared by a simple method. Various porous activated carbons are obtained using different types and concentrations of activator (KOH, KCl, and KHCO3). The effect of the microstructure on the electric heating performance of these carbons is investigated carefully. The type, activator concentration, and carbonization temperature play key roles in the regulation of electric heating properties. The porous carbon activated by 0.05 M KHCO3 at 800 °C demonstrates larger specific surface area (3077 m2 g-1), higher graphitization degree, and lower resistance (2.4 Ω cm), which synergistically contribute greatly to its higher electrothermal efficiency and better electric heating performance. The equilibrium temperature could reach 73 °C in 2 min under a safe voltage of 12 V, proving the better pore-forming capacity and activating function of KHCO3. An electric heating cotton@carbon composite fabric with quite good electric heating property and stability is also prepared, which could reach 38 °C in 2 min under 12 V safe voltage and maintain a temperature 10 °C higher than the ambient temperature even when bent at an angle of 55°. This activated carbon derived from waste protein using a simple and cheap process has great potential in practical applications.

Effects of nanostructuration on the electrochemical performance of metallic bioelectrodes.

The use of metallic nanostructures in the fabrication of bioelectrodes (e.g., neural implants) is gaining attention nowadays. Nanostructures provide increased surface area that might benefit the performance of bioelectrodes. However, there is a need for comprehensive studies that assess electrochemical performance of nanostructured surfaces in physiological and relevant working conditions. Here, we introduce a versatile scalable fabrication method based on magnetron sputtering to develop analogous metallic nanocolumnar structures (NCs) and thin films (TFs) from Ti, Au, and Pt. We show that NCs contribute significantly to reduce the impedance of metallic surfaces. Charge storage capacity of Pt NCs is remarkably higher than that of Pt TFs and that of the other metals in both morphologies. Circuit simulations of the electrode/electrolyte interface show that the signal delivered in voltage-controlled systems is less filtered when nanocolumns are used. In a current-controlled system, simulation shows that NCs provide safer stimulation conditions compared to TFs. We have assessed the durability of NCs and TFs for potential use in vivo by reactive accelerated aging test, mimicking one-year in vivo implantation. Although each metal/morphology reveals a unique response to aging, NCs show overall more stable electrochemical properties compared to TFs in spite of their porous structure.

A Hybrid Model for Reliability Aware and Energy-Efficiency in Multicore Systems

Recently, Multicore systems use Dynamic Voltage/Frequency Scaling (DV/FS) technology to allow the cores to operate with various voltage and/or frequencies than other cores to save power and enhance the performance. In this paper, an effective and reliable hybrid model to reduce the energy and makespan in multicore systems is proposed. The proposed hybrid model enhances and integrates the greedy approach with dynamic programming to achieve optimal Voltage/Frequency (Vmin/F) levels. Then, the allocation process is applied based on the available workloads. The hybrid model consists of three stages. The first stage gets the optimum safe voltage while the second stage sets the level of energy efficiency, and finally, the third is the allocation stage. Experimental results on various benchmarks show that the proposed model can generate optimal solutions to save energy while minimizing the makespan penalty. Comparisons with other competitive algorithms show that the proposed model provides on average 48% improvements in energy-saving and achieves an 18% reduction in computation time while ensuring a high degree of system reliability.