SEARCH · Engineering Papers

Results for “voltage limit”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18

All sources NASA NTRS DOE OSTI

DOE OSTI2025

Unified Model of Current-Limiting Grid-Forming Inverters for Large-Signal Analysis

Grid-forming (GFM) inverters can hardly withstand any overloading. As such, GFM inverters need a current limiter in their control system to avoid hardware damage during overloading or grid disturbances. When the current limiter is engaged for inverter protection, however, it dynamically changes the inverter output impedance, which can significantly affect the system behavior against large disturbances. For example, when the current limiter curtails the output power, the primary controller of the GFM inverter-which generates the voltage and angle reference-is prone to losing synchronization with the grid. This can cause large-signal instability in the network. This paper presents a unified GFM current-limiter model to gain a deeper understanding of the impact of the GFM inverter current limiting on large-signal instability and other system behaviors. The unified model captures several well-known current limiters for GFM inverters, and it reveals their large-signal equivalence characterized by the limiter angle. We use the unified model to present in-depth insights into the driving forces that cause large-signal instability in GFM inverter-driven grids. Further, this paper illustrates that the unified model can be used as a tool for assessing the system-level impacts of various GFM current-limiter designs during grid disturbances. Using numerical, analytical, electromagnetic transient models, and a hardware setup, the validity of the unified model is evaluated.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2026

Small-Signal Stability of Grid-Forming Converters Under Fault Conditions

Threshold virtual impedance (TVI)-based current limiting for grid-forming converters (GFMs) has gained great interest due to its ability to maintain voltage source behaviour during faults. However, sequence component extraction (SCE) and negative-sequence control (NSC) are often overlooked in small-signal stability assessments during faults. This paper develops small-signal sequence impedance models for GFMs under four well-known SCE methods based on TVI current limiting control during symmetrical fault conditions. Using the developed impedance models, the impacts of SCE and NSC, and the voltage and current control loop bandwidths, on system stability during faults are investigated. Additionally, since negative-sequence TVI (TVI-) is typically added along with its positive-sequence counterpart, which is often inductive, inductive and resistive TVI- are examined. The findings suggest that a higher voltage or current control loop bandwidth has a negative impact on system stability, while SCE and NSC largely reduce the stable range for voltage and current control loop bandwidth during faults, and that the severity of such impacts is determined by the particular SCE method. Furthermore, it is observed that inductive TVI- significantly degrades system stability, while resistive TVI- can enhance stability when suitable SCE methods are appropriately selected and designed. Matlab/Simulink electromagnetic transient simulations validate these analytical results.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2026

Interfacial and Kinetic Origins of Voltage Loss in Neutral Zinc‐Air Batteries

Rechargeable zinc-air batteries are promising candidates for grid-scale energy storage; however, their practical deployment is limited by oxygen electrocatalysis inefficiencies and interfacial instabilities, particularly outside conventional alkaline electrolytes. Here, in this work, zinc-air batteries operating under neutral electrolyte conditions using ZnCl 2 soaked KC-PAA-PAM gel polymer electrolytes and electrochemically synthesized Ni/Fe layered double hydroxide electrocatalysts is investigated. Ni/Fe-LDH is intentionally employed as an OER-biased benchmark catalyst to diagnose electrolyte and interface driven limitations rather than as a bifunctional ORR/OER solution. Full cells exhibit highly stable cycling over hundreds of hours, yet operate at substantially suppressed charge and discharge voltages relative to the thermodynamic value. Electrochemical impedance analysis shows that ohmic losses contribute only minimally to this voltage suppression. Post-mortem X-ray photoelectron spectroscopy reveals metallic zinc accumulation on the air cathode and chloride-containing species on the anode, indicating parasitic interfacial processes. Synchrotron-based soft X-ray absorption spectroscopy confirms stable Ni 2+ and Fe 3+ oxidation states during cycling, consistent with OER-biased catalytic behavior, while neutral-electrolyte oxygen evolution measurements demonstrate strong electrolyte-induced suppression of oxygen kinetics. Together, these results show that electrolyte chemistry and cathode-side parasitic processes, rather than catalyst identity alone, dominate voltage losses in neutral zinc-air batteries, providing mechanistic insight into the fundamental challenges associated with neutral electrolyte operation.

Long duration energy storage↗

DOE OSTI2021

Probabilistic Voltage Sensitivity based Preemptive Voltage Monitoring in Unbalanced Distribution Networks

With increasing penetration of renewable energy and active consumers, control and management of power distribution networks has become challenging. Renewable energy sources can cause random voltage fluctuations as their output power depends on weather conditions. Conventional voltage control schemes such as tap changers and capacitor banks lack the foresight required to quickly alleviate voltage violations. Thus, there is an urgent need for effective approaches for predicting and mitigating voltage violations as a result of random fluctuations in power injections. This work proposes a novel voltage monitoring approach based on low-complexity, data-driven probabilistic voltage sensitivity analysis. The usefulness of this work is not only in predicting voltage violations in unbalanced distribution grids, but also in opening up the door for optimal voltage control. Using system data and forecasts, the proposed approach predicts the distribution of system node voltages which is then used to to identify nodes that may violate the nominal operational limits with high probability. The method is tested on the IEEE 37 node distribution system considering integrated distributed solar energy sources. The method is validated against the classic load flow based method and offers over 95% accuracy in predicting voltage violations.

Abujubbeh, Mohammad↗

DOE OSTI2021

Studies of a modulated Hall thruster

A typical Hall thruster is powered from a DC power supply and operates with a constant discharge voltage. In operation, the discharge current is subject to strong low frequency oscillations (so-called breathing oscillations). Recent studies have shown that not only can these breathing oscillations be correlated with improved performance, but these oscillations can be induced and controlled by modulating the anode voltage. In this work, a systematic experimental study of the plasma flow in a modulated cylindrical Hall thruster was performed to characterize the effect of natural and modulated breathing oscillations on thruster performance. Measurements suggest that modulating the anode voltage in resonance with the natural breathing frequency does increase the thrust, but a corresponding phase alignment of discharge current and discharge voltage causes the efficiency gains to be insignificant. In addition, the outward shift of the acceleration region causes the plasma plume divergence to increase at the resonance condition and thereby, limit the thrust increase. Further, mechanisms underlying the relative phase between discharge current, ion current, and discharge voltage are investigated experimentally and corroborated with one-dimensional hybrid simulations of the thruster discharge.

modelling↗

DOE OSTI2025

LLM-Based Adaptive Distribution Voltage Regulation Under Frequent Topology Changes: An In-Context MPC Framework

This paper proposes a large language model (LLM) based adaptive inverter control for distribution voltage regulation under frequent topology changes. We leverage the ability of the LLM to perform in-context learning and create a topology-adaptive surrogate model for power flow calculation. The surrogate model is then integrated with a long short-term memory-based load forecaster and a model predictive control (MPC) scheme to achieve the optimal inverter control that adapts to frequent topology changes. Unlike many existing works that assume fixed-topology grids or require the knowledge of all possible topologies when training a model, the proposed in-context MPC method tackles the distribution voltage control problem under various topologies and adapts to unknown topologies with limited data requirement for fine-tuning. The effectiveness of our method is demonstrated on a modified IEEE 123-bus test system.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2021

F and N Rich Solid Electrolyte for Stable All-Solid-State Battery

We report the instability of sulfide solid electrolytes to Li anode and high-voltage LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathodes limits the cyclic performance of all-solid-state lithium battery (ASSLB). Herein, the stability of Li 6 PS 5 Cl against Li anode is enhanced by mixing a small amount (0.32 wt%) of CuF 2 -LiNO 3 (CL) into Li 6 PS 5 Cl electrolyte layer to in-situ form a mixed-conductive-lithiophobic and self-healing LiF-Li 3 N-Cu solid electrolyte interphase (SEI) at Li 6 PS 5 Cl-CL/Li interface. The critical current density (CCD) of Li 6 PS 5 Cl-CuF 2 -LiNO 3 increases to 1.4 mA cm –2 /1.4 mAh cm –2 at room temperature, which is much higher than that of pristine Li 6 PS 5 Cl (0.4 mA cm –2 /0.4 mAh cm –2 ) even though mixing 0.32 wt% CL into Li 6 PS 5 Cl slightly reduces the ionic conductivity from 2.9 × 10 –3 to 1.5 × 10 –3 S cm –1 . The compatibility of Li 6 PS 5 Cl-CL electrolyte to single-crystalline NMC811 (S-NMC811) is further enhanced by adding a small amount (0.02 wt%) of AlF 3 into Li 6 PS 5 Cl-CL forming Li 6 PS 5 Cl-CuF 2- LiNO 3 -AlF 3 (Li 6 >PS 5 Cl-CLA) as a cathode electrolyte and by doing Cl – on S-NMC811 (Cl@S-NMC811) surface. The Cl@S-NMC811-Li 6 PS 5 Cl-CLA|Li 6 PS 5 Cl-CL|Li cells with areal capacity of 2.55 mAh cm -2 achieve a capacity retention of 69.4% after 100 cycles at 1C (1C = 200 mAh g -1 ). Adding a small amount of SEI and cathode/electrolyte interphase (CEI) former into the sulfide electrolytes with minimal reduction (48.3%) of ionic conductivity is an effective method to enhance the performance of ASSLB.

36 MATERIALS SCIENCE↗

DOE OSTI2023

A theoretical thrust density limit for Hall thrusters

Abstract Hall Thrusters typically operate at thrust densities on the order of 10 N/m $$^2$$ 2 , which appear to be orders of magnitude below the thrust density limits suggested in previous literature. These limits have been considered here and each component of thrust density is analyzed to demonstrate the relative contribution to the total thrust density. Dependencies of the thrust density limits upon the thruster geometry, electron mobility, and the applied magnetic field are revealed and compared with experimental measurements of thrust density. This analysis reveals that with conventional applied magnetic field strengths, Hall thruster thrust density appears to be on the order of 1000 N/m $$^2$$ 2 . It is shown that this limit can be further increased through higher applied magnetic fields, applied voltage, and suppression of anomalous electron transport. This suggests Hall thrusters can be made much more compact and operated at higher power densities, given improvements to the thermal management and materials.

33 ADVANCED PROPULSION SYSTEMS↗

DOE OSTI2020

Eliminating dissolution of platinum-based electrocatalysts at the atomic scale

Deployment of proton-exchange membrane fuel cells is limited by the durability of Pt-nanoscale catalysts during cathodic oxygen reduction reactions. Dissolution processes on single crystalline and thin film surfaces are now correlated leading to the design of PtAu catalysts with suppressed dissolution. A remaining challenge for the deployment of proton-exchange membrane fuel cells is the limited durability of platinum (Pt) nanoscale materials that operate at high voltages during the cathodic oxygen reduction reaction. In this work, atomic-scale insight into well-defined single-crystalline, thin-film and nanoscale surfaces exposed Pt dissolution trends that governed the design and synthesis of durable materials. A newly defined metric, intrinsic dissolution, is essential to understanding the correlation between the measured Pt loss, surface structure, size and ratio of Pt nanoparticles in a carbon (C) support. It was found that the utilization of a gold (Au) underlayer promotes ordering of Pt surface atoms towards a (111) structure, whereas Au on the surface selectively protects low-coordinated Pt sites. Finally, this mitigation strategy was applied towards 3 nm Pt 3 Au/C nanoparticles and resulted in the elimination of Pt dissolution in the liquid electrolyte, which included a 30-fold durability improvement versus 3 nm Pt/C over an extended potential range up to 1.2 V.

36 MATERIALS SCIENCE↗

DOE OSTI2023

The Role and Value of Interregional Transmission in a Decarbonized U.S. Electricity System

Decarbonizing the U.S. energy system entails a significant expansion of wind and solar power and electrification of end-use applications. Achieving both is more efficient and less costly when interregional transmission capacity is expanded, but the fractured nature of grid planning in the United States is often a barrier to such expansion. Here, we explore the role of interregional transmission under a variety of decarbonization scenarios, using a capacity-expansion model to generate co-optimized portfolios of generation, storage, and transmission that meet decarbonization targets and electrification-driven demand. We explore portfolio and cost differences across 92 scenarios, from scenarios with limited transmission expansion to those that include a meshed high-voltage direct current (HVDC) network. In the core decarbonization scenarios, wind capacity expands by ~10x and solar by ~20x compared to 2020, hundreds of gigawatts of battery storage are deployed, and interregional transmission expands by 3-6x. Transmission expansion occurs nationwide but is concentrated between the central "wind belt" and eastern load centers. The HVDC scenarios result in hundreds of billions of dollars of savings in total system cost, demonstrating the economic benefits of interregional transmission in support of rapid decarbonization.

capacity expansion↗

DOE OSTI2021

Revealing Micro-Scale Doping Variations in Thin-Films via Simultaneous Luminescence and Current Collection Measurements

Doping thin films used for photovoltaic absorbers is both critical to maximize device voltage and challenging due to complex interactions between point defects in these materials. Such interactions can result in compensation of the intended dopant species, meaning that the active charge-carrier concentration is lower than the concentration incorporated dopants. Charge-carrier compensation is directly related to the open-circuit voltage (VOC) deficit, or magnitude of VOC relative to the theoretical limit. Understanding how the carrier concentration varies within thin-films is necessary to design material processing schedules to minimize this VOC deficit and produce more efficient devices. Unfortunately, measurements of the free carrier concentration are generally relevant at the device level and cannot resolve local differences. Resolving local doping differences in thin-films such as Cd(Se,Te), CZTS, and CIGSe requires techniques with micron or sub-micron spatial resolution due to the polycrystalline structure as well as intended and unintended composition variations in these materials. In this contribution, we show how simultaneous measurement of cathodoluminescence (CL) and electron-beam-induced current (EBIC) can be used to expose doping variations in Cd(Se,Te) thin-films. Simultaneous collection of these signals reveals unexpected differences in the electric field strength through the device thickness due to spatial variation in the carrier concentration.

41 EE - Solar Energy Technologies Office (EE-4S)↗

DOE OSTI2022

2022 Peer Review Project Summary: Advanced Protection for Microgrids and DER in Secondary Networks and Meshed Distribution Systems

Although there are increasing numbers of distributed energy resources (DERs) and microgrids being deployed, current IEEE and utility standards generally strictly limit their interconnection inside secondary networks. Secondary networks are low-voltage meshed (non-radial) distribution systems that create redundancy in the path from the main grid source to each load. This redundancy provides a high level of immunity to disruptions in the distribution system, and thus extremely high reliability of electric power service. There are two main types of secondary networks, called grid and spot secondary networks, both of which are used worldwide. In the future, primary networks in distribution systems that might include looped or meshed distribution systems at the primary-voltage (mediumvoltage) level may also become common as a means for improving distribution reliability and resilience. The objective of this multiyear project is to increase the adoption of microgrids in secondary networks and meshed distribution systems by developing novel protection schemes that allow for safe reliable operation of DERs in secondary networks. We will address these challenges by working with the appropriate stakeholders of secondary network operators, protection vendors, and standards committee. The outcomes of this project include: a) development and/or demonstration of candidate methods for enabling protection of secondary networks containing high levels of DER; b) development of modeling and testing tools for protection systems designed for use with secondary networks including DERs; and c) development of new industrial partnerships to facilitate widespread results dissemination and eventual commercialization of results as appropriate.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2023

City and Borough of Sitka, Alaska: Modeling and Controls Assistance and Renewable Energy Resource Assessment [Slides]

This project develops the dynamic modeling of hydro plants and wind generation in Sitka, Alaska. A dynamic penetration of renewables was evaluated under various conditions. The impact of altering hydro generation control to synchronous condenser control was evaluated. While the existing hydro generations are sufficient to address voltage instability, a detailed study of the active-reactive capability limits of hydro generation operation should be conducted to uptake at various wind penetration levels.

14 SOLAR ENERGY↗

DOE OSTI2024

Advanced Protection for Microgrids and DER in Secondary Networks and Meshed Distribution Systems

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2026

Revealing the Roles of CuF 2 /NiF 2 Incorporation in the Electrochemical Performance of FeF 3 Cathodes in Solid‐State Batteries

Mixed metal fluorides have been considered as a promising candidate to lower the voltage hysteresis of conversion-type iron fluoride cathodes, but their cycling stability is limited due to transition metal dissolution and interphase growth in liquid electrolyte batteries. Here, we study the role of incorporating CuF 2 and NiF 2 in the electrochemical performance of FeF 3 cathode in halide-based solid-state batteries to test whether we can transfer the kinetic benefit of low voltage hysteresis to solid-state batteries while using solid electrolyte to eliminate transition metal dissolution and stabilize the interphase. Synchrotron X-ray absorption spectroscopy results indicated the redox reactions are attributed to Cu 0 /Cu + and Fe 0 /Fe 2+ in 25CuF 2 -75FeF 3 and Ni 0 /Ni 2+ and Fe 0 /Fe 3+ in 10NiF 2 -90FeF 3 . While no apparent improvement in electrode kinetics can be observed, the incorporation of CuF 2 and NiF 2 can largely improve the cycling stability of FeF 3 cathodes. In conclusion, the results demonstrate the advantages of using solid-state concept to improve the cycling stability of conversion-type cathodes.

25 ENERGY STORAGE↗

DOE OSTI2024

A Simplified Method for Predicting Shaker Voltage in IMMATs

Impedance Matched Multi-Axis Tests (IMMATs) can replicate in-service vibration induced stress more accurately than single axis shaker table tests as they can better match a part’s operational boundary conditions and excite it in multiple degrees of freedom simultaneously. Here, the shakers used in IMMATs are less powerful than shaker tables, so shaker force limits can be exceeded during tests if they are not placed adequately for the desired environment. The ability to predict shaker voltage and force before performing a test is, therefore, helpful in selecting shaker locations so that their limits are not exceeded. In this study, electrodynamic shakers were modeled as discrete electromechanical systems, and the shaker parameters were chosen to match experimentally obtained acceleration/voltage frequency response functions (FRFs). These models were coupled to a finite element model of the device under test (DUT) via dynamic substructuring, and the substructured model was demonstrated to accurately predict shaker voltage as well as the error in reproducing the environment at multiple accelerometer locations. A simple method called the FRF Multiplication method, in which the FRF of the substructured system is approximated as the product of two separate FRFs of the shaker and DUT respectively, was proposed and applied to the same system, yielding similar voltage and error predictions to those obtained using substructuring. Simple case studies were presented to explore the applicability of the proposed method, and it was demonstrated to have similar accuracy to the substructuring method in a range of cases. Additionally, we showed that while it was not possible to derive a unique model of the shakers from acceleration/voltage FRFs alone, the models that could be obtained were sufficient to predict test error almost perfectly and shaker voltage with less than 40 percent error.

42 ENGINEERING↗

DOE OSTI2021

23.4% monolithic epitaxial GaAsP/Si tandem solar cells and quantification of losses from threading dislocations

A 2-terminal, dual-junction, epitaxially integrated, GaAsP/Si tandem solar cell with an 3rd party certified efficiency of 23.4 % was fabricated via MOCVD growth on an ex-situ produced Si sub cell. The drastic efficiency improvement over the authors previous peer-reviewed demonstration of such a device architecture is examined. Critical advancements in top cell design to maximize short wavelength response were critical in enabling improved top cell response. An in-depth analysis of this champion tandem cell has identified key loss mechanisms which elucidate the pathway for further efficiency gains. First, voltage dependent collection efficiency in the GaAsP top cell is the primary cause of fill factor losses currently limiting efficiency. Analysis of spectrally resolved I–V measurements and analytical device modeling and indicate poor diffusion length due to elevated dislocation densities as the likely cause for the voltage dependent collection efficiency. Second, modeling for the GaAs 0.75 P 0.25 top cell, using experimental data at multiple dislocation densities, provides quantitative understanding of the current and voltage losses associated with threading dislocations providing a clear efficiency pathway with reduction in dislocation density. Finally, Si subcell modeling identifies the pathway for further Si subcell advances over the present, simplistic design, which has yet to employ the known benefits of rear surface texture or dielectric passivation.

14 SOLAR ENERGY↗

DOE OSTI2023

Constraints on OPF Surrogates for Learning Stable Local Volt/Var Controllers

We consider the problem of learning local Volt/Var controllers in distribution grids (DGs). Our approach starts from learning separable surrogates that take both local voltages and reactive powers as arguments and predict the reactive power setpoints that approximate optimal power flow (OPF) solutions. We propose an incremental control algorithm and identify two different sets of slope conditions on the local surrogates such that the network is collectively steered toward desired configurations asymptotically. Our results reveal the trade-offs between each set of conditions, with coupled voltage-power slope constraints allowing an arbitrary shape of surrogate functions but risking limitations on exploiting generation capabilities, and reactive power slope constraints taking full advantage of generation capabilities but constraining the shape of surrogate functions. AC power flow simulations on the IEEE 37-bus feeder illustrate their guaranteed stability properties and respective advantages in two DG scenarios.

asymptotic stability↗