Ex situ bismuth doping for efficient CdSeTe thin-film solar cells with open-circuit voltages exceeding 900 mV
We dope CdTe solar cells with Bi after the device structure is completed using a solution process.
CdTe solar cell↗
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Results for “voltage exceedance”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Temperature control system with a pulse width modulated bridge
A temperature control system, which includes a modified wheatstone bridge with a resistive-capacitive (RC) circuit in one leg of the bridge, is disclosed. The RC circuit includes a resistor which provides an effective resistance as a function of its absolute resistance and the on-time to off-time ratio of pulses supplied to a switch connected across it. A sawtooth voltage is produced across the RC circuit. The voltage is compared with the voltage across a temperature sensor with heat being applied during each pulse period portion when the sawtooth voltage exceeds the voltage across the temperature sensor.
Heyser, R. C.↗
Voltage monitoring system
A description is given of a system for monitoring the voltage at a remote location and determining when the voltage exceeds upper and lower levels. The system includes transmission lines for transmitting the voltage back to a central station and applying such to an amplifier having a pair of outputs. One of the outputs of the amplifier is applied to an oscillograph. The other output is fed through an isolation transformer, a full wave rectifier, to a pair of unijunctional transistor circuits for producing pulses when the voltage exceeds or drops below a predetermined level. These pulses, in turn, energize a relay which turns on the oscillograph for recording the voltages being monitored.
Canicatti, C. L.↗
Hybrid circuit achieves pulse regeneration with low power drain
Hybrid tunnel diode-transistor circuit provides a solid-state, low power drain pulse regenerator, frequency limiter, or gated oscillator. When the feedback voltage exceeds the input voltage, the circuit functions as a pulse normalizer or a frequency limiter. If the circuit is direct coupled, it functions as a gated oscillator.
Cancro, C. A.↗
High-Voltage Photogeneration Exclusively via Aggregation-Induced Triplet States in a Heavy-Atom-Free Nonplanar Organic Semiconductor
The electron–hole recombination kinetics of organic photovoltaics (OPVs) are known to be sensitive to the relative energies of triplet and charge-transfer (CT) states. Yet, the role of exciton spin in systems having CT states above 1.7 eV—like those in near-ultraviolet-harvesting OPVs—has largely not been investigated. Here, aggregation-induced room-temperature intersystem crossing (ISC) to facilitate exciton harvesting in OPVs having CT states as high as 2.3 eV and open-circuit voltages exceeding 1.6 V is reported. Triplet excimers from energy-band splitting result in ultrafast CT and charge separation with nonradiative energy losses of <250 meV, suggesting that a 0.1 eV driving force is sufficient for charge separation, with entropic gain via CT state delocalization being the main driver for exciton dissociation and generation of free charges. This finding can inform engineering of next-generation active materials and films for near-ultraviolet OPVs with open-circuit voltages exceeding 2 V. Contrary to general belief, this work reveals that exclusive and efficient ISC need not require heavy-atom-containing active materials. Molecular aggregation through thin-film processing provides an alternative route to accessing 100% triplet states on photoexcitation.
25 ENERGY STORAGE↗
Transient Voltage Recorder
A voltage transient recorder can detect lightning induced transient voltages. The recorder detects a lightning induced transient voltage and adjusts input amplifiers to accurately record transient voltage magnitudes. The recorder stores voltage data from numerous monitored channels, or devices. The data is time stamped and can be output in real time, or stored for later retrieval. The transient recorder, in one embodiment, includes an analog-to-digital converter and a voltage threshold detector. When an input voltage exceeds a pre-determined voltage threshold, the recorder stores the incoming voltage magnitude and time of arrival. The recorder also determines if its input amplifier circuits clip the incoming signal or if the incoming signal is too low. If the input data is clipped or too low, the recorder adjusts the gain of the amplifier circuits to accurately acquire subsequent components of the lightning induced transients.
Pedro J Medelius↗
Simulation-Based Analysis of Feeder Operation with Different PV Smart Inverter Functions on an Actual Distribution System: Preprint
High penetration of photovoltaics (PV) in distribution feeders can cause problems, such as overvoltage, reverse power flow, and large net load changes. Traditional voltage regulation devices, such as capacitors and voltage regulators, can solve some of these problems but might have some delays. Today, smart inverters are gradually being used to provide voltage regulation and frequency support in distribution systems. Different smart inverter settings have been recommended in various rules and standards; however, the potential benefits and their impacts on distribution system operation are not well compared and studied. This paper presents a comparison of different smart inverter settings as applied to a distribution system. An actual feeder model from San Diego Gas & Electric Company is used to conduct the simulation. Additionally, a load disaggregation method is proposed to disaggregate the load and PV profile for each load location using advanced metering infrastructure net load measurements. Then, different smart inverter settings are applied to the PV systems in the feeder, and the simulation results are compared. The results show that the implementation of specific functions of smart inverters can reduce voltage exceedances, and the utility can determine the specific inverter setting based on its operational requirements.
distribution system↗
A data-driven sensor placement approach for detecting voltage violations in distribution systems
Stochastic fluctuations in power injections from distributed energy resources (DERs) combined with load variability can cause constraint violations (e.g., exceeded voltage limits) in electric distribution systems. To monitor grid operations, sensors are placed to measure important quantities such as the voltage magnitudes. Here, in this paper, we consider a sensor placement problem which seeks to identify locations for installing sensors that can capture all possible violations of voltage magnitude limits. We formulate a bilevel optimization problem that minimizes the number of sensors and avoids false sensor alarms in the upper level while ensuring detection of any voltage violations in the lower level. This problem is challenging due to the nonlinearity of the power flow equations and the presence of binary variables. Accordingly, we employ recently developed conservative linear approximations of the power flow equations that overestimate or underestimate the voltage magnitudes. By replacing the nonlinear power flow equations with conservative linear approximations, we can ensure that the resulting sensor locations and thresholds are sufficient to identify any constraint violations. Additionally, we apply various problem reformulations to significantly improve computational tractability while simultaneously ensuring an appropriate placement of sensors. Lastly, we improve the quality of the results via an approximate gradient descent method that adjusts the sensor thresholds. We demonstrate the effectiveness of our proposed method for several test cases, including a system with multiple switching configurations.
24 POWER TRANSMISSION AND DISTRIBUTION↗
Acceleration Factors for Reliability Assessment of Polymer Tantalum Capacitors
Using polymer tantalum capacitors in Hi-Rel systems requires an assessment of the reliability characteristics of the parts. For this assessment, tantalum capacitors are typically subjected to reliability testing at temperatures and voltages exceeding their specified values, and the failure rate (FR) — or the probability of failure during use conditions — is calculated based on voltage and temperature acceleration factors. In this work, various types and lots of polymer tantalum capacitors have been tested at highly accelerated life test (HALT) conditions and the acceleration factors have been determined using different techniques. It has been shown that the behavior of capacitors under HALT conditions can be described based on the time-dependent dielectric breakdown (TDDB) model, which explains the presence of infant mortality (IM) and wear-out failures using the same failure mechanisms and allows for an assessment of the acceleration factors. The difference in acceleration factors obtained using exponential and power models is discussed. Analysis shows that with proper derating, screening, and qualification testing, the reliability of frameless Hi-Rel COTS polymer tantalum capacitors is adequate for space missions.
Alex Eidelman↗
Acceleration Factors for Reliability Assessment of Polymer Tantalum Capacitors
Using polymer tantalum capacitors in Hi-Rel systems requires an assessment of the reliability characteristics of the parts. For this assessment, tantalum capacitors are typically subjected to reliability testing at temperatures and voltages exceeding their specified values, and the failure rate (FR) — or the probability of failure during use conditions — is calculated based on voltage and temperature acceleration factors. In this work, various types and lots of polymer tantalum capacitors have been tested at highly accelerated life test (HALT) conditions and the acceleration factors have been determined using different techniques. It has been shown that the behavior of capacitors under HALT conditions can be described based on the time-dependent dielectric breakdown (TDDB) model, which explains the presence of infant mortality (IM) and wear-out failures using the same failure mechanisms and allows for an assessment of the acceleration factors. The difference in acceleration factors obtained using exponential and power models is discussed. Analysis shows that with proper derating, screening, and qualification testing, the reliability of frameless Hi-Rel COTS polymer tantalum capacitors is adequate for space missions.
Alex Eidelman↗
Development of a multiplexed bypass control system for aerospace batteries
A breadboard bypass control system was developed to control a battery comprised of 26 JPL-developed negative limited Ni-Cd cells. The system was designed to automatically remove cells from the circuit when their voltages exceeded a fixed limit on charge and fell below a fixed limit on discharge. Major components of the system consisted of a cell voltage monitor, a multiplexing circuit, and individual electromechanical relays for each cell. The system was found to function well in controlling the battery during a simulated 10-month MM-71 mission and a 2-month simulated low earth orbit cycling mission. A flight version of the bypass system was estimated to have a total parts count of 150 and total weight of 1.63 kg. When fully developed, the system shows promise for improving life and reliability of spacecraft batteries.
Frank, H. A.↗
Model Quality and Measurement Density Impact on Volt/Volt Ampere Reactive Optimization Performance
The operation of the utility grid is being reshaped by the continuous addition of distributed energy resources and advanced metering infrastructure, which challenge existing grid control strategies. Some utilities deploy advanced distribution management systems (ADMS) to assist with the consolidation of various applications and to augment situational awareness in response to the new power delivery dynamics. An ADMS is an integrated software platform that provides utilities with a way to enhance their reliability, control, and optimization with advanced applications, such as volt/VAR optimization (VVO). A VVO application could serve as a vehicle to deliver cost savings by providing the utility with a method to reduce rates by controlling the voltage and decreasing the energy usage in their service territory. Some utilities are reluctant to integrate an ADMS, because it is a significant investment that requires approval from the public regulatory commission and/or their customers. This paper evaluates the impact on VVO performance when using a lower-quality network model supplemented with additional measurements, which could provide an implementation for cost savings. The results show that a better model quality would provide the highest energy savings; however, some level of telemetry is necessary in all scenarios to prevent voltage exceedances.
24 POWER TRANSMISSION AND DISTRIBUTION↗
Mild pH-decoupling aqueous flow battery with practical pH recovery
Establishing a pH difference between the two electrolytes (pH decoupling) of an aqueous redox flow battery (ARFB) enables cell voltages exceeding the 1.23 V thermodynamic water-splitting window, but acid–base crossover penalizes efficiency and lifetime. Here we employ mildly acidic and mildly alkaline electrolytes to mitigate crossover, achieving high round-trip energy efficiency with open circuit voltage >1.7 V. We implemented an acid–base regeneration system to periodically restore electrolytes to their initial pH values. The combined system exhibited capacity fade rate <0.07% per day, round-trip energy efficiency >85% and approximately 99% Coulombic efficiency during stable operation for over a week. Cost analysis shows that the tolerance of acid–base crossover could be increased if the pH-decoupling ARFB achieved a higher voltage output and lower resistance. Finally, this work demonstrates principles for improving lifespan, rate capability and energy efficiency in high-voltage pH-decoupling ARFBs and pH recovery concepts applicable for pH-decoupling systems.
25 ENERGY STORAGE↗
Arsenic doped Cd-rich CdTe: equilibrium doping limit and long lifetime for high open-circuit voltage solar cells greater than 900 mV
The combination of group-V element doping and Cd-rich composition is the most promising current strategy for maximizing p-type doping while preserving long lifetime. In this study, we carefully measure the equilibrium p-type doping limit for As-doped Cd-rich CdTe single crystals and demonstrate a doping limit in the low 10 17 cm –3 range upon slow cooling. Here, we present evidence for self-compensation with rapidly decreasing doping efficiency per added As above 5 × 10 16 cm –3 , yet we also demonstrate CdTe with >10 17 cm –3 hole concentration and bulk lifetime >30 ns. Such crystals allow As-doped CdTe photovoltaic devices with open-circuit voltage exceeding 900 mV.
14 SOLAR ENERGY↗
Enabling Stable High‐Voltage LiCoO 2 Operation by Using Synergetic Interfacial Modification Strategy
Abstract Structural and interfacial instability of the LiCoO 2 cathode under a voltage exceeding 4.5 V (vs Li/Li + ) severely hinders its practical applications for high‐energy‐density lithium batteries. Herein, a modified electrolyte with nitriles (suberonitrile or 1,3,6‐hexanetricarbonitrile) and fluoroethylene carbonate (FEC) coadditives is demonstrated to form an ultrathin and uniform interface layer on LiCoO 2 cathode under a synergetic effect. As such, LiCoO 2 /Li cells display excellent cyclability at a cutoff voltage of 4.6 V with a capacity retention over 72% after 300 cycles and 60% after 200 cycles at 30 and 55 °C, respectively, even achieving operation at a high current rate (10 C) upon 500 cycles as compared to the controls with fast‐falling capacity to zero. Furthermore, an adsorption‐coordination mechanism between nitriles and cobalt and synergetic effect of coadditives are explored by the alliance of spectroscopic analysis and theoretical calculations. The contributed lone‐pairs on the N 2p orbital of nitriles in coordination lowers the real oxidation state of Co 3+/4+ so that it decreases its catalysis on electrolytes, and the synergy from nitrile‐derived species regulates FEC to form an LiF‐containing electron‐insulated interface layer. This work shares a new insight to nitriles with the synergy of coadditives and paves a way to refine (ultra)high‐voltage LiCoO 2 cathode for high‐energy‐density energy storages.
Yang, Xuerui↗
Environmental Testbed Development to Evaluate Power Distribution Materials in Electrified Aircraft (EA)
NASA is pursuing the development of electrified propulsion (EP) technologies to improve air transportation in terms of efficiency, affordability, and sustainability. The power requirements are expected to reach 20 megawatts for large EP commercial airliners. A key challenge is transmission and distribution of the high voltage (20 kilovolts) needed for some EP systems. This is a challenge because the risk of electrical failure in aircraft at high altitude (low pressure) due to corona discharge and other forms of partial discharge increases significantly when voltages exceed 327 V. Corona discharge is a form of partial discharge in which gaseous molecules are ionized by strong electric fields. Corona discharge leads to aging in power transmission lines. Aging is a leading cause of electrical failure in electrical insulation materials. In particular, aging from electrical, vibrational, and thermal stresses decrease the performance life of insulation materials. There are currently no test standards or equipment that can effectively age materials under high altitude, voltage and frequency conditions. This poster proposes a design for a test system including an environmental chamber that can simulate the environment of future EP systems for material and component aging tests.
Materials Test chamber Design↗
High-voltage AlN Schottky barrier diodes on bulk AlN substrates by MOCVD
Abstract This letter reports the demonstration of Aluminum nitride (AIN) Schottky barrier diodes on bulk AlN substrates by metalorganic chemical vapor phase deposition with breakdown voltages exceeding 3 kV. The devices exhibited good rectifying characteristics with ON/OFF ratios of 10 6 –10 8 and excellent thermal stability from 298 to 623 K. The device Schottky barrier height increased from 0.89 to 1.85 eV, and the ideality factor decreased from 4.29 to 1.95 with increasing temperature, ascribed to the inhomogeneous metal/AlN interface. This work demonstrates the potential of AlN as an ultra-wide bandgap semiconductor for developing multi-kV AlN high-voltage and high-power devices.
Physics↗
20 kV Gallium Nitride pn Diode Electro-Magnetic Pulse Arrestor for Grid Reliability (Final Scientific/Technical Report)
This project developed vertical Gallium Nitride (GaN) pn diodes under two main thrusts: (1) A focus on relatively higher-voltage devices for use as fast EMP arrestors to protect the electric grid; and (2) A focus on a Foundry effort to establish the manufacturability of relatively lower voltage devices. For the first thrust, the aim was to develop devices that go into avalanche breakdown to clamp the voltage across sensitive grid equipment subject to voltage transients induced by electromagnetic pulses (EMPs). Devices with breakdown voltages exceeding 6.5 kV were achieved, and breakdown times shorter than 1 ns were demonstrated, which is sufficiently fast to protect against the fast component of an EMP-induced signal. Key challenges included the epitaxial growth of thick (50 µm or more), low-doped (low 10 15 cm -3 range) GaN layers comprising the drift regions of the diodes, as well as the design and fabrication of edge termination structures (step-etched junction termination extensions) to prevent premature breakdown. Midway through the project, an additional emphasis was put on large-area, high-current devices, and forward currents of approximately 400 A were achieved in composite devices towards the end of the project. Experimental and theoretical studies of impact ionization and avalanche ruggedness were also conducted. For the second thrust (the Foundry), the focus was primarily on 1.2-kV-class devices, although towards the end of the project outstanding results on 3.3-kV class devices were also achieved. The aim of the Foundry was to develop a high-yield, reliable, and economic vertical GaN pn diode process. The Foundry conducted characterization of incoming epitaxial material and correlated this information with the yield and performance of fully processed devices. Wafer maps of diode characteristics such as forward and reverse current as well as capacitance-voltage curves were measured using auto-probing. Several mask sets comprising different-area devices as well as multiple edge termination designs (implanted junction termination extensions, guard rings, and combinations thereof) were studied, and machine-learning-based approaches were utilized to analyze the data. Packaging and reliability efforts were also undertaken for the Foundry diodes, which are necessary for a viable commercial process.
20KV↗