Safe Voltage Research Articles

Facile Synthesis of NiMoO4 Nanorod Electrode for Aqueous Hybrid Supercapacitor with High Energy Density

NiMoO4 nanorods (NRs) were successfully fabricated on Ni foam with robust adhesion via a simple and cost-effective hydrothermal treatment, followed by a calcined process. In a three-electrode configuration with 3 mol L−1 KOH aqueous solution. The NiMoO4 NRs supported on Ni foam as working electrodes achieve a high specific capacity of 1320 C g−1 at a charge and discharge current density of 2 mA cm−2, and a desirable rate capability (884 C g−1 even at 10 mA cm−2) and a superior cycling ability with 88% capacity retention after 4000 cycles at 10 mA cm−2. To enhance the energy density and enlarge the voltage window, the aqueous hybrid supercapacitor has subsequently been constructed by employing the NiMoO4 and activated carbon electrodes as positive and negative electrodes, respectively, which delivered a high energy density of 52 Wh kg−1 at a power density of 725 W kg−1. Impressively, the device indicates a long-term cycling stability with capacitance retention of 123% even after 9000 cycles in aa safe voltage range from 0 V to 1.45 V. These results definitely imply the promising prospect of NiMoO4 NR electrodes for application in supercapacitors.

Constructing Safe and Durable High‐Voltage P2 Layered Cathodes for Sodium Ion Batteries Enabled by Molecular Layer Deposition of Alucone

AbstractSodium ion batteries are a promising next‐generation energy storage device for large‐scale applications. However, the high voltage P2–O2 phase transition (>4.25 V vs Na/Na+) and metal dissolution of P2 layered cathodes into the electrolyte result in severe capacity fading, which is a major setback to fabricate high energy devices. Hence, it is essential to design an appropriate strategy to enhance interfacial behaviors to obtain safe and stable high voltage sodium ion batteries. Herein, an ultrathin alucone layer deposited through molecular layer deposition (MLD) is employed to stabilize the structure of a P2‐type layered cathode cycled at a high cut‐off voltage (>4.45 V) for the first time. The alucone coated P2‐type Na0.66Mn0.9Mg0.1O2 (NMM) cathode exhibits an 86% capacity retention after 100 cycles between 2 and 4.5 V at 1 C, demonstrating substantial improvement compared to pristine (65%) and Al2O3‐coated (71%) NMM cathodes. Furthermore, the mechanically robust and conductive nature of the organometallic thin film enhances the rate capability relative to the pristine NMM electrode. This work reveals that the MLD of alucone on cathodes is a promising approach to improve the cycle stability of sodium ion batteries at high cut‐off voltages.

Characterization of Li Diffusion and Solid Electrolyte Interface for Li4Ti5O12 Electrode Cycled with an Organosilicon Additive Electrolyte

The use of lithium titanate (Li4Ti5O12, LTO) for the negative electrode in lithium ion batteries has attracted enormous attention owing to its fast charging capability, high power, safe operating voltage window and stable structure (“zero strain”) during cycling. Researchers have investigated the formation of the solid electrolyte interface (SEI) of the LTO electrode, which prevents gassing issue and leads to longer cycle life. In this study, the solid-state diffusion property of LTO at room temperature was characterized using AC impedance spectroscopy at different states of charge (SOC) during charge and discharge to reveal the dependency of the lithium diffusion coefficient on SOC. Meanwhile the formation and growth of the solid electrolyte interface (SEI) on the LTO electrode using an electrolyte containing Silatronix OS3® additive were investigated using X-ray photoelectron spectroscopy (XPS). The composition of the SEI and its evolution due to cycling with the OS3® additive was compared to that with a commercial electrolyte. Half-cell coin cells of LTO vs lithium metal were formed and cycled at room temperature for over 200 cycles, where the resistance increase, as measured by impedance spectroscopy, is correlated to the SEI growth. Electrode samples were analyzed in the pristine state, after formation, and after 200 cycles. XPS results showed that a thin layer of SEI is formed during the first two formation cycles and the composition of the SEI on the surface of the LTO electrode varied with increasing cycle number. Based on the escape depths of Ti 3 s and Ti 2p regions, the SEI after formation is thicker than 5.5 nm but is less than 7.0 nm for both the OS3® and A7 electrolytes. Based on Ar-ion depth profiling, the SEI thickness in terms of the equivalent thickness of SiO2 after 200 cycles in coin cell configuration is estimated to be near 14 nm for both the OS3® and A7 electrolytes. A much higher fluorine content (F 1s peak) was found in the SEI formed with the OS3® electrolyte than the SEI formed with the commercial A7 electrolyte.

DC-Patch: A Microarchitectural Fault Patching Technique for GPU Register Files

The ever-increasing parallelism demand of General-Purpose Graphics Processing Unit (GPGPU) applications pushes toward larger and more energy-hungry register files in successive GPU generations. Reducing the supply voltage beyond its safe limit is an effective way to improve the energy efficiency of register files. However, at these operating voltages, the reliability of the circuit is compromised. This work aims to tolerate permanent faults from process variations in large GPU register files operating below the safe supply voltage limit. To do so, this paper proposes a microarchitectural patching technique, DC-Patch, exploiting the inherent data redundancy of applications to compress registers at run-time with neither compiler assistance nor instruction set modifications. Instead of disabling an entire faulty register file entry, DC-Patch leverages the reliable cells within a faulty entry to store compressed register values. Experimental results show that, with more than a third of faulty register entries, DC-Patch ensures a reliable operation of the register file and reduces the energy consumption by 47% with respect to a conventional register file working at nominal supply voltage. The energy savings are 21% compared to a voltage noise smoothing scheme operating at the safe supply voltage limit. These benefits are obtained with less than 2 and 6% impact on the system performance and area, respectively.

Effect of measuring distance error on working phase voltage at zero potential live working point

When the live working is carried out in the distribution network, the zero-potential charging operation is often used. The safety of zero-potential live working is closely related to the measurement distance error. The influence of the measurement error of the zero-potential live working point on the operating phase voltage needs to be studied. Based on the Floyd algorithm, a method for calculating the shortest electrical distance from the operating point to the substation is proposed. The sub-station is centered on the branch nodes of the line to form the distance matrix, and the Floyd algorithm is used to calculate the shortest electrical distance from the working point to the substation. The working phase injection voltage is further calculated based on the zero phase potential characteristics of the operating phase. Finally, based on the PSCAD, the system model is established. The simulation concludes that the distance between the substation and the working point is less than 20m, and the operating point voltage can still be below the safe voltage.

A Novel Modularizing Design Method of 10 kV High Voltage Switchgear for Live Maintenance

Due to imperfect manufacturing technology, design defects and environmental impact, the failure rate of 10 kV switchgear is very high. For this reason, based on taken present situation of traditional switchgear and the current technical requirements for switchgear into account, a new reliable and safe modular high voltage switchgear design method is presented in this paper, which can reduce the failure rate of switchgear and improve the reliability of power supply. The electric field and temperature rise simulation model are established to check the reasonability and validity. By using the finite element software, the simulation results show that the design in this paper has a maximum temperature rise of 55 K for the main cabinet and a maximum temperature rise of 45 K for the deputy cabinet, which is far below the international standard of 70 K. The areas where the partial discharge is likely to occur within the switchgear are places such as the connection between bus-bar and cabinet, bus-bar joint and bus-bar corner. In order to avoid potential dangers, the discharge point must be located in time to prevent insulation fault of electrical equipment of the high voltage switchgear. The simulation results demonstrate that the design method in this paper greatly improve the reliability of switchgear and meets the demands of power system.

Safety Analysis of Offshore Platform Power System Considering Low Voltage Crossing Capability

In the face of increasingly serious energy and environmental problems, the safety of offshore oil drilling and production platform, as a natural gas development platform, is of great significance. For offshore platforms, the offshore power system serves for oil and gas production, and the interruption or shutdown of oil and gas production caused by electric power is intrinsically unsafe; In addition, due to the weak interconnection between the offshore platform systems, with the characteristics of small unit, large load, wide application of frequency conversion equipment and poor environment, the security analysis of the offshore platform power system must take the power grid and gas network as a whole to analyze and take into account the low-voltage crossing capacity. For the coupling of power grid and gas network of offshore platform, multi-stage compression system and the “power to gas” system are proposed. For these voltage sag sensitive systems, the safe critical voltage and critical cut-off time are used to characterize the low-voltage crossing capability. The operation constraints considering the low-voltage crossing capability are also proposed, and the impact of voltage sag is taken into account in the safety analysis. The simulation results show the correctness of the safety analysis method considering the low voltage crossing capability, and the necessity of the safety analysis considering the gas network and the low crossing capability.

Designing and Fabrication of Switching High Voltage Power Supply for Nuclear Medicine Imaging Systems

This paper describes design considerations of the High voltage (HV) module with low ripple and good stability in order to improve the efficiency of nuclear imaging systems consist of Single Photon Emission Computed Tomography (SPECT). In the design of the current HV module, push-pull topology is preferred, due to the fact; it has a better efficiency in comparison with other technologies. The module receives a positive continuous voltage about 5-8 V as input, and provides a programmable positive or negative continuous voltage from 800-2500 V as output for a total load of 200-KΩ. The ripple of the output voltage is 10 mV that it is measured by laboratory equipment’s and safe high voltage (SHV) probe. The measured output power in the designed module is 25 W. Experiment results show that minimum efficiency at full load is around 65%. The proposed HV module shows a good stability, low ripple (noise), fast rise time. So, it can be used in SPECT or gamma camera imaging system to provide the constant voltage for PMTS.

Transparent Electrothermal Film Defoggers and Antiicing Coatings based on Wrinkled Graphene.

Fog, frost, ice, and other natural phenomena can inevitably affect human life and the function of equipment. Therefore, removal or prevention is an urgent problem to be solved. As a new type of 2D material, graphene possesses great application potential in defogging and antiicing. In this work, a graphene film with intentionally increased defects and uniformly distributed wrinkles is synthesized on copper-zinc alloy substrates by chemical vapor deposition, and transparent electrothermal film defoggers are prepared based on such material. The defoggers can completely remove fog within 5 s when supplying a safe voltage of 28 V. The surface resistance of the defoggers is sensitive to humidity and it can monitor the defogging process in real time. Such outstanding performance is attributed to the ultrafast evaporation mechanism, which can prevent excessive water accumulation. The antiicing performance of wrinkled graphene (WG) is further studied. The antiicing coatings can delay freezing for 1.25 h at -15 °C or 2.8 h at -10 °C. The superior performance of WG can be explained by its unique surface structure and nanoscale roughness. Taken together, WG is expected to be used in antifog glass, rearview mirror defogging, aircraft surface deicing, and other applications.

Influence of cut-off voltage on the lithium storage performance of Nb12W11O63 anode

The niobium tungsten oxide Nb12W11O63 is synthesized by a simple solid-state method and studied as an anode for lithium-ion batteries. By comparing with graphite anode, Nb12W11O63 with orthorhombic structure has higher safe working voltage (˃1.70 V) and tap density (∼2.57 g cm−3). The effect of cut-off voltage on the electrochemical property is also analyzed in detail. X-ray diffraction results reveal the mechanism of performance deterioration in Nb12W11O63 under deep discharge, which is caused by the collapse of crystal structure due to the transformation of pentagonal bipyramid to octahedron induced by excessive Nb3+. At the cut-off voltage of 1.3 V, Nb12W11O63 electrode delivers excellent electrochemical performances with high initial coulombic efficiency of 94.7%, improved cycling stability of 146 mAh g−1 after 404 cycles at 113 mA g−1 (78.8% of capacity retention) and good rate capacity of 100 mAh g−1 at 4520 mA g−1. These results indicate that Nb12W11O63 is a promising anode for lithium-ion batteries, and also provide the insight into the performance optimization of such materials.

A Series Stacked IGBT Switch Based on a Concentrated Clamp Mode Snubber for Pulsed Power Applications

Clamp mode snubbers are very well suited for the series structure of the insulated-gate bipolar transistors (IGBTs) in pulsed power applications. They properly meet the necessities expected from them such as the fast operating of the series IGBTs since they have no effect on the gate side. In addition, they can provide safe voltage condition for the IGBTs in short circuit faults, which are very probable in pulsed applications. The clamp mode snubber can perform its voltage balancing task whenever the power capacity of the snubber can support the injected powers due to the voltage unbalancing factors. This paper initially introduces the main factors injecting power to the snubbers. Then, it will be illustrated that the exact injected power to each predetermined snubber cannot be determined due to the uncertainties about the effect of the voltage unbalancing factors. Although it is impossible to determine the exact value of the power injected to each snubber, the total injected powers to the snubbers can be calculated. Therefore, as an effective remedy, this paper proposes a concentrated snubber. Using the proposal, all the injected powers are conducted to a centralized circuit and can be easily managed. In addition, analytical expressions are provided for proper dimensioning of the proposed concentrated snubber elements. Furthermore, the performance of the proposed concentrated snubber is evaluated using simulations and experimental prototyping.

Computational Investigation of the Binding Energy and Electrochemical Stability of Poly(ethylene oxide) with Li-Ion Salts

The increasing awareness to maximize the use of energy resources has led to exploration in effective energy storage viz. high energy density batteries which are reliable, cost-effective and have low energy losses. This has spearheaded the development of solid polymer electrolytes for safer lithium-ion batteries with comparable properties to conventional liquid electrolyte-based lithium-ion batteries. Since the polymer functions as the electrolyte as well as the separator, they must possess a number of critical properties to seamlessly function in the battery. The electrochemical stability window (ESW) is a critical consideration which determines the safe operational voltage outside which the electrolyte degrades. Another factor is the Li-binding energy of the ions to the polymer which is a prelude to the Li-ion migration in the electrolyte and provides an estimate of the solubility of the salt in the polymer matrix. An optimal binding energy is desired where it is high enough for the Li-ion to bind to the polymer but not high enough to prevent its migration through the electrolyte. In this work, molecular dynamics (MD) and density functional theory (DFT) calculations are performed to determine the ESW and the binding energy of polyethylene oxide (PEO), an excellent inflammable and stable polymer electrolyte with multiple Li salts namely, LiBr, LiCl, LiI, LiClO4, LiSCN, LiCH3COO, LiNO3, LiBH4, LiCF3SO3 and LiBF4 to ascertain realistic ESW and binding energy values. We establish a relationship between the effects of the salt anion on the ESW and the binding energy. The ESW decreases in the presence of a salt in the polymer host, and we explore the effects of the salt anion size on the ESW. We also determine an optimal binding energy range for PEO with the salts which successfully propagates polymer-salt solvation as well as Li-ion migration. We believe this study should be able to guide the experimental design of stable and safe solid polymer electrolytes in the future.

Modeling of Dynamic Current Distribution in REBCO Insulated Coils Using a Volume Integral Formulation for Protection Purpose

Dynamic current distribution in HTS coils submitted to current ramps induces a varying inductive voltage, which can be problematic for safe quench detection as its order of magnitude may hide the increasing dissipative voltage appearing at the beginning of a transition. In order to estimate the transient voltage component, which depends on the coil geometry as well as the current profile and the coil magnetization state, we developed a model using a Volume Integral formulation based on a generalization of the Partial Element Equivalent Circuit method. The objective is to split the coil's voltage end-to-end value into an inductive and a dissipative component so as to evaluate a safe voltage threshold value to implement in the detection system, enabling early transition detection to prevent the coil from major damages. The model is compared to experimental data and its application to coil's protection is detailed on a small-scale test coil.

Sinusoidal alternating current heating strategy and optimization of lithium-ion batteries with a thermo-electric coupled model

In order to solve the application bottleneck of electric vehicles in alpine-cold regions, sinusoidal alternating current heating becomes a competitive method. A novel thermo-electric coupled model for lithium-ion power batteries at low temperatures is proposed in this paper. The model combines the thermal model with the electrochemical impedance model. Model parameters are identified by genetic algorithm through programming in MATLAB. Plenty of experiments have validated the model and explored the influence factors of the heat generation effect. It is found that as the battery temperature increases, the optimal current amplitude increases gradually, whereas the optimal current frequency decreases. Therefore, an original temperature dependent control approach of sinusoidal alternating current heating is proposed and the strategy is optimized by sequential quadratic programming algorithm, considering safe operating voltage constraints. The optimal frequency range is distributed in the high frequency region, which makes the allowable safe current larger and thus gives a larger heat generation rate, and lithium ion deposition does not occur. Finally, the optimized heating strategy is verified by experiments. Results show that the battery module can achieve a temperature rise from −20 °C to 0 °C in 520 s, with an average temperature-rise 2.31 °C/min.

Power management improvement of hybrid energy storage system based on H [formula omitted] control

This paper deals with the real-time implementation of a robust control for electric vehicles, supplied by a battery/capacitor super capacitor hybrid energy storage system (HESS) and piloted via a permanent magnet synchronous motor (PMSM). The main goals are to monitor the motor using the back-stepping control and to provide an efficient power management. This has been implemented by means of the DC bus regulation using an H∞ regulator, while a classical regulator is used to ensure a super capacitor (SC) voltage allowing a maximal availability during repetitive peak power, in order to ensure an optimal power flow to the load as well as to keep the SC operation in a safe voltage range. This original algorithm has been validated through experimental results provided by a tailor made test bench including both the HESS and the vehicle emulation controlled via two dSPACE 1104 cards. Furthermore, the back-stepping controller shows good dynamic performances, where the system reaches to track perfectly the speed profile, under tolerable torque and flux ripples.

Fuzzy-Super twisting control implementation of battery/super capacitor for electric vehicles

The present paper deals with a real-time implementation of a novel Fuzzy logic energy management strategy (EMS), applied to a battery–super capacitor hybrid energy system and associated with a permanent magnet synchronous motor (PMSM) which emulates the traction part of an electric vehicle (EV). On the sources side, the fuzzy logic supervisor acts in a smart way to permute smoothly between the various operations modes via an efficient power frequency splitting. In addition, it permits a quite regulation of both the DC bus and the super-capacitor (SC) voltages regardless of the speed profile variations to ensure an optimal power flow to the load and to keep the SC operation in a safe voltage range while providing or absorbing power in transients. On the traction side, a second order sliding mode control called ‘super-twisting’ (ST), associated with a space vector modulation (SVM) strategy is applied to ensure both decoupled torque and flux control under low torque and flux ripples. The assessment of the proposed control techniques is conducted on a small-scale battery/SC/PMSM system, controlled via two dSPACE1104 cards. The obtained experimental results show a smooth operation of the whole system, where the proposed Fuzzy logic supervisor succeeds to provide fast and high performances under different speed levels and ensures the proper functioning of each source while respecting its dynamics. Furthermore, the second order sliding mode controller shows good dynamic performances, where the system arrives to track perfectly the speed profile, under tolerable torque and flux ripples.

Effect of Proton Irradiation on Breakdown Field of Hexagonal Boron Nitride

Hexagonal boron nitride (h-BN) is widely used as a two-dimentional (2D) insulating material. Owing to its high breakdown field (8-12 MV/cm), wide band gap (5.2-5.9 eV), and thermal⋅chemical stability, h-BN is employed as a dielectric layer of 2D integrated electronic device. Unlike to other insulating materials, h-BN has an atomically flat surface free from the dangling bond at the interface. Therefore, it is less affected by trap charges and mismatch of the lattice structure. Without any complicated process, it is possible to obtain an atomically thin flake by mechanical exfoliation and is easy to apply to extremely thin electronic device application such as field effect transistor and complementary metal-oxide semiconductor. Dielectric layer of semiconductor device must maintain its insulating property in extreme condition. It is of great importance to find out the breakdown field to ensure the stability of the device. However, the atoms constituting the lattice of the insulator can be damaged by protons, heavy ions and cosmic rays. These rays make an irreversible degradation on the insulating materials, and the destruction of the lattice structure can be accompanied. It poses a critical hazard on the performance of the device in that degradation of insulator lead to lower the breakdown field of dielectric layer. Measurement of changes of the breakdown field by radiation can define the safe operating voltage range of the device. H-BN is a next-generation insulating material, but the effect of radiation on h-BN has not been fully studied. In this work, we quantitatively analyzed the damage on h-BN and effect on breakdown field from varying proton-ray irradiation conditions. We fabricated pre-patterned source/drain electrode of Ti/Au on a Si/SiO2 wafer. A thin h-BN flake was mechanically exfoliated from the high-crystalline h-BN bulk crystal. Prepared flakes were transferred to the substrate by dry transfer method. We employed atomic force microscope to measure the thickness of h-BN. H-BN flakes were proton-irradiated under varying condition of power (5MeV, 10MeV) and fluence (1×1013, 5×1013). To measure breakdown field, graphene was used as a top electrode on h-BN to creat a vertical structure. We proceeded a electrical measurement to find out the hard breakdown field of pristine and irradiated h-BN flakes respectively. Mean value of the breakdown field of pristine h-BN flakes is 10.532 MV/cm, comparable with value of reported exfoliated h-BN. Whereas the breakdown field of proton-irradiated h-BN flakes ranged from 1 to 7 MV/cm. We used density functional theory and molecular dynamics simulation to estimate the mechanism of damaging on the lattice structure of h-BN. Proton irradiation causes irreversible degradation on atomic structure of h-BN, such as interstitial or vacant defects. This triggered a sudden current jump and failure at a lower voltage. We can enable more stable operation by considering the expected breakdown field of the device under the condition of radiation. Details of our work will be discussed in the presentation.

Rational design of Sn-Sb-S composite with yolk-shell hydrangea-like structure as advanced anode material for sodium-ion batteries

To circumvent the poor cycling stability of 2D layered metal sulfide, a novel yolk-shell hydrangea-like Sn-Sb-S microflower composite self-assembled by nanosheets, was successfully designed and fabricated as anode material for sodium-ion batteries. Without any introduction of carbonaceous materials, the Sn-Sb-S microflower composite could possess prominent sodium-ion storage properties through constructing Sb-rich phase with superior cycling stability as the protective shell to envelop the higher-capacity yolk Sn-rich phase. The yolk-shell Sn-Sb-S microflower composite exhibits a first discharge capacity of 1601.1 mAh/g. A highly reversible capacity of >600 mAh/g with a favorable and safe average voltage of ∼0.6 V was achieved, constituting a promising anode material for sodium-ion batteries.

Joining together theory and practice in the classroom for electrical engineering undergraduates: The large-scale portable laboratory

Teaching electrical engineering requires a combination of theoretical and practical lessons to acquire knowledge and develop skills. However, in general, laboratory sessions are conducted separately from theoretical lessons for practical reasons. We shall describe a proposal to bridge the gap between theoretical explanation or exercises and practical application in a laboratory: the large-scale portable laboratory. This temporary laboratory can be set up and then collected again in a conventional classroom in just a few minutes. By using safe voltages and currents it allows us to illustrate and immediately apply theoretical concepts or to discover some phenomena, which can then be explained theoretically. It is a tool to connect experimental observations and theoretical explanations during student learning. This laboratory has some physical limitations and does not replace practical sessions in an electrical engineering laboratory. A full session with this laboratory will be described and the results obtained will subsequently be presented. As a result, student involvement dramatically increases. It provided good results in learning and helped the electric laboratory sessions. Some difficulties such as preparation time and time spent during the session are also discussed.

Material stiffness control of compliant tools by using electromagnetic suction

Variable rigidity materials that are safe, controllable, reversible, and repeatable have potentially widespread implications in robotic technologies. This paper presents a method for controlling the stiffness of materials for compliant tools, such as grippers, soft robots, and endoscopes. The force of electromagnetic suction transforms two structures from their relaxed-state into a more rigid state. The system presented here has the ability of quickly increasing the stiffness with increased current in the coils that create electromagnetic suction, wherein the stiffness can be controlled by the variation of supply current. The process of controlling stiffness variation is reversible and repeatable under the safe voltage of human body. The system can lead to the production of tools that are small, flexible, dexterous, and safe. Suction force, friction force, and rotational stiffness were calculated to evaluate the performance of the system. Experiments were carried out to verify the proposed concept and the calculations.