Showing papers on "Voltage published in 2016"

Guanidinium: A Route to Enhanced Carrier Lifetime and Open-Circuit Voltage in Hybrid Perovskite Solar Cells

Abstract: Hybrid perovskites have shown astonishing power conversion efficiencies owed to their remarkable absorber characteristics including long carrier lifetimes, and a relatively substantial defect tolerance for solution-processed polycrystalline films. However, nonradiative charge carrier recombination at grain boundaries limits open circuit voltages and consequent performance improvements of perovskite solar cells. Here we address such recombination pathways and demonstrate a passivation effect through guanidinium-based additives to achieve extraordinarily enhanced carrier lifetimes and higher obtainable open circuit voltages. Time-resolved photoluminescence measurements yield carrier lifetimes in guanidinium-based films an order of magnitude greater than pure-methylammonium counterparts, giving rise to higher device open circuit voltages and power conversion efficiencies exceeding 17%. A reduction in defect activation energy of over 30% calculated via admittance spectroscopy and confocal fluorescence intensi...

Voltage Stability Of Electric Power Systems

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Modular battery powered handheld surgical instrument with energy conservation techniques

Abstract: A method of conserving energy in a surgical instrument that includes a segmented circuit having a plurality of independently operated circuit segments, a voltage control circuit, an energy source, a memory, and a processor coupled to the memory. The processor is configured to control a state of a circuit segment of the plurality of circuit segments. The state can be an energized state or a deenergized state. The method includes transmitting an energizing signal from the processor to a voltage control circuit, receiving the energizing signal by the voltage control circuit to apply a voltage to a circuit segment of the plurality of circuit segments, applying the voltage to the circuit segment by the voltage control circuit to cause the circuit segment to transition from the deenergized state to the energized state in accordance with an energization sequence that is different from a deenergization sequence.

The Effect of Distributed Parameters on Conducted EMI from DC-Fed Motor Drive Systems in Electric Vehicles

Abstract: The large dv/dt and di/dt outputs of power devices in DC-fed motor drive systems in electric vehicles (EVs) always introduce conducted electromagnetic interference (EMI) emissions and may lead to motor drive system energy transmission losses. The effect of distributed parameters on conducted EMI from the DC-fed high voltage motor drive systems in EVs is studied. A complete test for conducted EMI from the direct current fed(DC-fed) alternating current (AC) motor drive system in an electric vehicle (EV) under load conditions is set up to measure the conducted EMI of high voltage DC cables and the EMI noise peaks due to resonances in a frequency range of 150 kHz–108 MHz. The distributed parameters of the motor can induce bearing currents under low frequency sine wave operation. However the impedance of the distributed parameters of the motor is very high at resonance frequencies of 500 kHz and 30 MHz, and the effect of the bearing current can be ignored, so the research mainly focuses on the distributed parameters in inverters and cables at 500 kHz and 30 MHz, not the effect of distributed parameters of the motor on resonances. The corresponding equivalent circuits for differential mode (DM) and common mode (CM) EMI at resonance frequencies of 500 kHz and 30 MHz are established to determine the EMI propagation paths and analyze the effect of distributed parameters on conducted EMI. The dominant distributed parameters of elements responsible for the appearing resonances at 500 kHz and 30 MHz are determined. The effect of the dominant distributed parameters on conducted EMI are presented and verified by simulation and experiment. The conduced voltage at frequencies from 150 kHz to 108 MHz can be mitigated to below the limit level-3 of CISPR25 by changing the dominant distributed parameters.

Power and Voltage Balance Control of a Novel Three-Phase Solid-State Transformer Using Multilevel Cascaded H-Bridge Inverters for Microgrid Applications

Abstract: This paper presents a new application of power and voltage balance control schemes for the cascaded H-bridge multilevel inverter (CHMI)-based solid-state transformer (SST) topology. To reduce load on the controller and simplify modulation algorithm, a master–slave control (MSC) strategy is designed for the dual active bridge (DAB) stage. The master controller executes all control and modulation calculations, and the slave controllers manage only device switching and protection. Due to the inherent power and dc-link voltage unbalance in cascaded H-bridge-based SST, this paper presents a compensation strategy based on three-phase dq decoupled current controller. An optimum zero-sequence component is injected in the modulation scheme so that the three-phase grid currents are balanced. Furthermore, to tightly regulate the output voltage of all the DAB modules to target value, a dynamic reference voltage method is also implemented. With this proposed control method, the three-phase grid currents and dc-link voltage in each module can be simultaneously balanced. Finally, simulation and experimental results are presented to validate the performance of the controller and its application to microgrid SST.

Centralized Charging Strategy and Scheduling Algorithm for Electric Vehicles Under a Battery Swapping Scenario

Abstract: Centralized charging of electric vehicles (EVs) based on battery swapping is a promising strategy for their large-scale utilization in power systems. The most outstanding feature of this strategy is that EV batteries can be replaced within a short time and can be charged during off-peak periods or on low electric price and scheduled in any battery swap station. This paper proposes a novel centralized charging strategy of EVs under the battery swapping scenario by considering optimal charging priority and charging location (station or bus node in a power system) based on spot electric price. In this strategy, a population-based heuristic approach is designed to minimize total charging cost, as well as to reduce power loss and voltage deviation of power networks. We introduce a dynamic crossover and adaptive mutation strategy into a hybrid algorithm of particle swarm optimization and genetic algorithm. The resulting algorithm and several others are executed on an IEEE 30-bus test system, and the results suggest that the proposed one is effective and promising for optimal EV centralized charging.

Hole‐Transporting Materials in Inverted Planar Perovskite Solar Cells

Abstract: Hybrid organic–inorganic halide-perovskite-based solar cells have achieved notable progress. A hot topic in this field is exploring inexpensive, stable and effective hole-transporting materials (HTMs) in order to improve the device performance and be favorable for large-scale production in the future. The HTMs have been proven to be an important component of perovskite solar cells, which can form selective contact being favorable for reducing charge recombination and effective hole collection, thus resulting in the enhancement of the open-circuit voltage and the fill factor. Here, an overview of the design and development of HTMs is given, mainly divided into conductive polymers, inorganic p-type semiconductors in inverted-structure-based planar perovskite solar cells. The influences of their mobility, work function and film property on device performance are discussed.

A New Cascaded Switched-Capacitor Multilevel Inverter Based on Improved Series–Parallel Conversion With Less Number of Components

Abstract: The aim of this paper is to present a new structure for switched-capacitor multilevel inverters (SCMLIs) which can generate a great number of voltage levels with optimum number of components for both symmetric and asymmetric values of dc-voltage sources. The proposed topology consists of a new switched-capacitor dc/dc converter (SCC) that has boost ability and can charge capacitors as self-balancing by using the proposed binary asymmetrical algorithm and series–parallel conversion of power supply. The proposed SCC unit is used in new configuration as a submultilevel inverter (SMLI) and then, these proposed SMLIs are cascaded together and create a new cascaded multilevel inverter (MLI) topology that is able to increase the number of output voltage levels remarkably without using any full H-bridge cell and also can pass the reverse current for inductive loads. In this case, two half-bridge modules besides two additional switches are employed in each of SMLI units instead of using a full H-bridge cell that contribute to reduce the number of involved components in the current path, value of blocked voltage, the variety of isolated dc-voltage sources, and as a result, the overall cost by less number of switches in comparison with other presented topologies. The validity of the proposed SCMLI has been carried out by several simulation and experimental results.

Operation Modes for the Electric Vehicle in Smart Grids and Smart Homes: Present and Proposed Modes

Abstract: This paper presents the main operation modes for an electric vehicle (EV) battery charger framed in smart grids and smart homes, i.e., present-day and new operation modes that can represent an asset toward EV adoption are discussed and proposed, respectively. Apart from the well-known grid-to-vehicle (G2V) and vehicle-to-grid (V2G) operation modes, this paper proposes two new operation modes: home-to-vehicle (H2V), where the EV battery charger current is controlled according to the current consumption of the electrical appliances of the home (this operation mode is combined with G2V and V2G), and vehicle-for-grid (V4G), where the EV battery charger is used for compensating current harmonics or reactive power, simultaneously with the G2V and V2G operation modes. The vehicle-to-home (V2H) operation mode, where the EV can operate as a power source in isolated systems or as offline uninterruptible power supply to feed priority appliances of the home during power outages of the electrical grid, is presented in this paper and framed with the other operation modes. These five operation modes were validated through experimental results using a developed 3.6-kW bidirectional EV battery charger prototype, which was specially designed for these operation modes. This paper describes the developed EV battery charger prototype, detailing the power theory and the voltage and current control strategies used in the control system. This paper also presents experimental results for the various operation modes, both in steady state and during transients.

Inverted Current–Voltage Hysteresis in Mixed Perovskite Solar Cells: Polarization, Energy Barriers, and Defect Recombination

Abstract: Organic-inorganic metal halide perovskite solar cells show hysteresis in their current-voltage curve measured at a certain voltage sweep rate. Coinciding with a slow transient current response, the hysteresis is attributed to a slow voltage-driven (ionic) charge redistribution in the perovskite solar cell. Thus, the electric fi eld profi le and in turn the electron/hole collection effi ciency become dependent on the biasing history. Commonly, a positive prebias is benefi cial for a high power-conversion effi ciency. Fill factor and open-circuit voltage increase because the prebias removes the driving force for charge to pile-up at the electrodes, which screen the electric fi eld. Here, it is shown that the piled-up charge can also be benefi cial. It increases the probability for electron extraction in case of extraction barriers due to an enhanced electric fi eld allowing for tunneling or dipole formation at the perovskite/electrode interface. In that case, an inverted hysteresis is observed, resulting in higher performance metrics for a voltage sweep starting at low prebias. This inverted hysteresis is particularly pronounced in mixed-cation mixed-halide systems which comprise a new generation of perovskite solar cells that makes it possible to reach power-conversion effi ciencies beyond 20%.

Beyond Bulk Lifetimes: Insights into Lead Halide Perovskite Films from Time-Resolved Photoluminescence

Abstract: In the quest for better solar panels, we continue to refine our understanding of the physics of photovoltaic absorbers, such as hybrid metal-organic perovskites By scrutinizing photoluminescence transients, the authors explain how to determine fundamental semiconductor properties and estimate the potential open-circuit voltage of perovskite thin films Additionally, they highlight the impacts of photon recycling, doping, and bulk and surface recombination of charge carriers on device performance

Ultra-low switching energy and scaling in electric-field-controlled nanoscale magnetic tunnel junctions with high resistance-area product

Abstract: We report electric-field-induced switching with write energies down to 6 fJ/bit for switching times of 0.5 ns, in nanoscale perpendicular magnetic tunnel junctions (MTJs) with high resistance-area product and diameters down to 50 nm. The ultra-low switching energy is made possible by a thick MgO barrier that ensures negligible spin-transfer torque contributions, along with a reduction of the Ohmic dissipation. We find that the switching voltage and time are insensitive to the junction diameter for high-resistance MTJs, a result accounted for by a macrospin model of purely voltage-induced switching. The measured performance enables integration with same-size CMOS transistors in compact memory and logic integrated circuits.

Bulk-Type All Solid-State Batteries with 5 V Class LiNi0.5Mn1.5O4 Cathode and Li10GeP2S12 Solid Electrolyte

Abstract: All solid-state batteries are of key importance in the development of next-generation energy storage devices with high energy density. Herein, we report the fabrication and operation of bulk-type 5 V-class all solid-state batteries consisting of LiNi0.5Mn1.5O4 cathode, Li10GeP2S12 solid-electrolyte, and Li metal anode. The 1st discharge capacity is about 80 mAh g–1 with an average voltage of 4.3 V. The discharge capacity gradually decreases during the subsequent cycles. X-ray diffraction and electrochemical impedance spectroscopy measurements reveal that the capacity fading results from the growth of a resistive interfacial layer on the cathode composite. The development of suitable conductive additive and sulfide solid electrolyte materials is essential for the development of high-voltage all solid-state batteries.

CH3 NH3 PbBr3 -CH3 NH3 PbI3 Perovskite-Perovskite Tandem Solar Cells with Exceeding 2.2 V Open Circuit Voltage.

Abstract: Perovskite-perovskite tandem solar cells with open-circuit voltages of over 2.2 V are reported. These cost-effective, solution-processible perovskite hybrid tandem solar cells with high open-circuit voltages are fabricated by the simple lamination of a front planar MAPbBr3 perovskite cell and a back MAPbI3 planar perovskite solar cell.

A Bidirectional Nonisolated Multi-Input DC–DC Converter for Hybrid Energy Storage Systems in Electric Vehicles

Abstract: To process the power in hybrid energy systems using a reduced part count, researchers have proposed several multiinput dc–dc power converter topologies to transfer power from different input voltage sources to the output. This paper proposes a novel bidirectional nonisolated multi-input converter (MIC) topology for hybrid systems to be used in electric vehicles composed of energy storage systems (ESSs) with different electrical characteristics. The proposed converter has the ability to control the power of ESSs by allowing active power sharing. The voltage levels of utilized ESSs can be higher or lower than the output voltage. The inductors of the converter are connected to a single switch; therefore, the converter requires only one extra active switch for each input, unlike its counterparts, hence resulting in reduced element count. The proposed MIC topology is compared with its counterparts concerning various parameters. It is analyzed in detail, and then, this analysis is validated by simulation and through a 1-kW prototype based on a battery/ultracapacitor hybrid ESS.

Neuromorphic Learning and Recognition With One-Transistor-One-Resistor Synapses and Bistable Metal Oxide RRAM

Abstract: Resistive switching memory (RRAM) has been proposed as an artificial synapse in neuromorphic circuits due to its tunable resistance, low power operation, and scalability. For the development of high-density neuromorphic circuits, it is essential to validate the state-of-the-art bistable RRAM and to introduce small-area building blocks serving as artificial synapses. This paper introduces a new synaptic circuit consisting of a one-transistor/one-resistor structure, where the resistive element is a HfO2 RRAM with bipolar switching. The spike-timing-dependent plasticity is demonstrated in both the deterministic and stochastic regimes of the RRAM. Finally, a fully connected neuromorphic network is simulated showing online unsupervised pattern learning and recognition for various voltages of the POST spike. The results support bistable RRAM for high-performance artificial synapses in neuromorphic circuits.

A High-Current, Stable Nonaqueous Organic Redox Flow Battery

Abstract: Nonaqueous redox flow batteries are promising in pursuit of high energy density storage systems owing to the broad voltage windows (>2 V) but currently are facing key challenges such as limited cyclability and rate performance. To address these technical hurdles, here we report the nonaqueous organic flow battery chemistry based on N-methylphthalimide anolyte and 2,5-di-tert-butyl-1-methoxy-4-[2′-methoxyethoxy]benzene catholyte, which harvests a theoretical cell voltage of 2.30 V. The redox flow chemistry exhibits excellent cycling stability under both cyclic voltammetry and flow cell tests upon repeated cycling. A series of Daramic and Celgard porous separators are evaluated in this organic flow battery, which enable the cells to be operated at greatly improved current densities as high as 50 mA cm–2 compared to those of other nonaqueous flow systems. The stable cyclability and high-current operations of the organic flow battery system represent significant progress in the development of promising nonaqu...

Dual-Space Vector Control of Open-End Winding Permanent Magnet Synchronous Motor Drive Fed by Dual Inverter

Abstract: This paper proposes a dual-space vector control scheme for the open-end winding permanent magnet synchronous motor (OEW-PMSM) drive fed by the dual inverter with a single dc supply. Potential zero-sequence current in the open-end winding drive system has to be considered since it causes circulating current in the winding and leads to high current stress of power semiconductor devices and high losses. Zero-sequence current in open-end winding ac motor drives is usually caused by the zero-sequence voltage, and therefore switching combinations which do not produce zero-sequence voltage are used to synthesize the reference voltage in existing methods. But even so, the zero-sequence voltage can also be produced by the dead time of the inverter. In order to suppress zero-sequence current in the OEW-PMSM drive, a dual-space vector control scheme is proposed and a novel dual-inverter space vector pulse width modulation (PWM) with the zero-sequence voltage reference is employed to regulate system zero-sequence voltage in this paper. Compared with existing dual inverter PWM strategies, the novel algorithm build a regulation mechanism for the zero-sequence voltage. The proposed method is compared with the conventional vector control by simulations and experiments, and the results shown that the proposed scheme can suppress zero-sequence current effectively.

Improved performance low-cost incremental conductance PV MPPT technique

Abstract: Variable-step incremental conductance (Inc.Cond.) technique, for photovoltaic (PV) maximum power point tracking, has merits of good tracking accuracy and fast convergence speed. Yet, it lacks simplicity in its implementation due to the mathematical division computations involved in its algorithm structure. Furthermore, the conventional variable step-size, based on the division of the PV module power change by the PV voltage change, encounters steady-state power oscillations and dynamic problems especially under sudden environmental changes. In this study, an enhancement is introduced to Inc.Cond. algorithm in order to entirely eliminate the division calculations involved in its structure. Hence, algorithm implementation complexity is minimised enabling the utilisation of low-cost microcontrollers to cut down system cost. Moreover, the required real processing time is reduced, thus sampling rate can be improved to fasten system response during sudden changes. Regarding the applied step-size, a modified variable-step size, which depends solely on PV power, is proposed. The latter achieves enhanced transient performance with minimal steady-state power oscillations around the MPP even under partial shading. For proposed technique's validation, simulation work is carried out and an experimental set up is implemented in which ARDUINO Uno board, based on low-cost Atmega328 microcontroller, is employed.

Ab Initio Study of Phosphorus Anodes for Lithium- and Sodium-Ion Batteries

Abstract: Phosphorus has received recent attention in the context of high-capacity and high-rate anodes for lithium- and sodium-ion batteries. Here, we present a first-principles structure prediction study combined with NMR calculations, which gives us insights into its lithiation/sodiation process. We report a variety of new phases found by the ab initio random structure searching (AIRSS) and the atomic species swapping methods. Of particular interest, a stable Na5P4–C2/m structure and locally stable structures found less than 10 meV/f.u. from the convex hull such as Li4P3–P212121, NaP5–Pnma, and Na4P3–Cmcm. The mechanical stability of Na5P4–C2/m and Li4P3–P212121 has been studied by first-principles phonon calculations. We have calculated average voltages, which suggest that black phosphorus (BP) can be considered as a safe anode in lithium-ion batteries due to its high lithium insertion voltage, 1.5 V; moreover, BP exhibits a relatively low theoretical volume expansion compared with other intercalation anodes, 2...

A Review of Galvanically Isolated Impedance-Source DC–DC Converters

Abstract: Impedance-source converters, an emerging technology in electric energy conversion, overcome limitations of conventional solutions by the use of specific impedance-source networks. Focus of this paper is on the topologies of galvanically isolated impedance-source dc–dc converters. These converters are particularly appropriate for distributed generation systems with renewable or alternative energy sources, which require input voltage and load regulation in a wide range. We review here the basic topologies for researchers and engineers, and classify all the topologies of the impedance-source galvanically isolated dc–dc converters according to the element that transfers energy from the input to the output: a transformer, a coupled inductor, or their combination. This classification reveals advantages and disadvantages, as well as a wide space for further research. This paper also outlines the most promising research directions in this field.

Coil Design and Measurements of Automotive Magnetic Resonant Wireless Charging System for High-Efficiency and Low Magnetic Field Leakage

Abstract: For wireless charging of electric vehicle (EV) batteries, high-frequency magnetic fields are generated from magnetically coupled coils. The large air-gap between two coils may cause high leakage of magnetic fields and it may also lower the power transfer efficiency (PTE). For the first time, in this paper, we propose a new set of coil design formulas for high-efficiency and low harmonic currents and a new design procedure for low leakage of magnetic fields for high-power wireless power transfer (WPT) system. Based on the proposed design procedure, a pair of magnetically coupled coils with magnetic field shielding for a 1-kW-class golf-cart WPT system is optimized via finite-element simulation and the proposed design formulas. We built a 1-kW-class wireless EV charging system for practical measurements of the PTE, the magnetic field strength around the golf cart, and voltage/current spectrums. The fabricated system has achieved a PTE of 96% at the operating frequency of 20.15 kHz with a 156-mm air gap between the coils. At the same time, the highest magnetic field strength measured around the golf cart is 19.8 mG, which is far below the relevant electromagnetic field safety guidelines (ICNIRP 1998/2010). In addition, the third harmonic component of the measured magnetic field is 39 dB lower than the fundamental component. These practical measurement results prove the effectiveness of the proposed coil design formulas and procedure of a WPT system for high-efficiency and low magnetic field leakage.

Electric-Field-Induced Degradation of Methylammonium Lead Iodide Perovskite Solar Cells.

Abstract: Perovskite solar cells have great potential for high efficiency generation but are subject to the impact of external environmental conditions such as humidity, UV and sun light, temperature, and electric fields. The long-term stability of perovskite solar cells is an important issue for their commercialization. Various studies on the stability of perovskite solar cells are currently being performed; however, the stability related to electric fields is rarely discussed. Here the electrical stability of perovskite solar cells is studied. Ion migration is confirmed using the temperature-dependent dark current decay. Changes in the power conversion efficiency according to the amount of the external bias are measured in the dark, and a significant drop is observed only at an applied voltage greater than 0.8 V. We demonstrate that perovskite solar cells are stable under an electric field up to the operating voltage.