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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Stability Analysis of Power Systems with High Penetration of State-of-the-Art Inverter Technologies

With the increasing level of inverter-based resources (IBRs) in modern power systems, this paper presents a small-signal stability analysis for power systems comprising synchronous generators (SGs) and IBRs. Four types of inverter controls are considered: two grid-following (GFL) controls, with or without grid support functions; droop-based grid-forming (GFM) controls; and virtual oscillator control-based GFM. We also analyze the impact of STATCOM and synchronous condensers on system stability to assess their role in the energy mix transition. With the small-signal dynamic behavior of the major technologies modeled, this paper provides stringent stability assessments using the IEEE 39-bus benchmark system modified to simulate future power systems. The exhaustive test cases allow for (a) assessing the impacts of different types and controls of generation and supplementary grid assets, as well as system inertia and line impedance on grid stability, and (b) elucidating pathways for the stabilization of IBR-dominated power systems. The analysis also indicates that future power systems can be stabilized with only a fraction of the total generation as voltage sources without SGs or significant system inertia if they are well distributed. This study provides insights into future power system operations with a high level of IBRs that can also be used for planning and operation studies.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2024

Assessing cathode–electrolyte interphases in batteries

The cathode-electrolyte interphase plays a pivotal role in determining the usable capacity and cycling stability of electrochemical cells, yet it is overshadowed by its counterpart, the solid-electrolyte interphase. This is primarily due to the prevalence of side reactions, particularly at low potentials on the negative electrode, especially in state-of-the-art Li-ion batteries where the charge cutoff voltage is limited. However, as the quest for high-energy battery technologies intensifies, there is a pressing need to advance the study of cathode-electrolyte interphase properties. Here, we present a comprehensive approach to analyse the cathode-electrolyte interphase in battery systems. We underscore the importance of employing model cathode materials and coin cell protocols to establish baseline performance. Additionally, we delve into the factors behind the inconsistent and occasionally controversial findings related to the cathode-electrolyte interphase. In conclusion, we also address the challenges and opportunities in characterizing and simulating the cathode-electrolyte interphase, offering potential solutions to enhance its relevance to real-world applications.

25 ENERGY STORAGE↗
DOE OSTI2024

Thermodynamic, Kinetic, and Transport Contributions to Hydrogen Evolution Activity and Electrolyte-Stability Windows for Water-in-Salt Electrolytes

Concentrated water-in-salt electrolytes (WiSEs) are used in aqueous batteries and to control electrochemical reactions for fuel production. The hydrogen evolution reaction is a parasitic reaction at the negative electrode that limits cell voltage in WiSE batteries and leads to self-discharge, and affects selectivity for electrosynthesis. Mitigating and modulating these processes is hampered by a limited fundamental understanding of HER kinetics in WiSEs. Here, in this study, we quantitatively assess how thermodynamics, kinetics, and interface layers control the apparent HER activities in 20 m LiTFSI. When the LiTFSI concentration is increased from 1 to 20 m, an increase in proton activity causes a positive shift in the HER equilibrium potential of 71 mV. The exchange current density, i o , derived from the HER branch for 20 m LiTFSI in 98% purity (0.56 ± 0.05 μA/cm Pt 2 ), however, is 8 times lower than for 20 m LiTFSI in 99.95% (4.7 ± 0.2 μA/cm Pt 2 ) and 32 times lower than for 1 m LiTFSI in 98% purity (18 ± 1 μA/cm Pt 2 ), demonstrating that the WiSE's impurities and concentration are both central in significantly suppressing HER kinetics. The ability and applicability of the reported methods are extended by examining additional WiSEs formulations made of acetates and nitrates.

25 ENERGY STORAGE↗
DOE OSTI2024

Grid-Forming Inverters for Stability Improvements in Bulk Power Systems with High Inverter-Based Resources Penetration

The grid-forming inverter (GFM) has been considered recently as a means to enhance grid stability in areas with Inverter-based Resources (IBRs) concentration. This paper assesses the potential improvements the GFM can bring to Bulk-power Systems (BPS) through two distinct studies. The first study was conducted on West Texas in ERCOT with presence of more than 35GW of IBRs, the Grid-Following (GFL) batteries were replaced with GFM batteries. The results demonstrate that the GFM significantly improved the voltage profile and active power injection during and after a fault. The second study focused on a local area within ERCOT grid. In this case, a battery operating as GFL within the local study area was replaced with a GFM battery. The findings clearly illustrate that GFM can strengthen the area and allow a higher IBRs power generation and a higher power export from the local study area.

Quedan, Amro↗
DOE OSTI2025

Oscillation Risks of Grid-Following and Grid-Forming Inverter-Based Resources in Series-Compensated Networks

Here, this paper investigates the dynamic behavior of a grid-connected inverter-based resource (IBR) when connected radially to a series compensated line. Potential interactions between the series compensation and the IBR have been identified for both types: grid-following (GFL) or grid-forming (GFM). The study begins with electromagnetic transient (EMT) simulations to demonstrate stability issues. Subsequently, nonlinear analytical models are formulated in the dq frame, validated against the EMT simulation, and leveraged to assess eigenvalues and participation factors. Influencing factors of the dominant oscillation modes have been identified. The analysis results show that series compensation may make a mode associated with the synchronization unit unstable. Furthermore, customized feedback systems are built for the synchronizing loop. Series compensation can increase the sensitivity of the voltage phase angle towards the synchronizing angle, and introduce phase lag in the real power response towards the synchronizing angle. These factors may cause interactions with the phase-locked loop in GFL-IBR systems and with power-based synchronization in GFM-IBR systems, potentially leading to instability.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2026

Transient Stability Study of IEEE 2800-2022 Standard Negative-Sequence-Current Compliant GFM IBRs

The primary function of grid-forming (GFM) inverter-based resources (IBRs) is to maintain voltage and fre- quency/phase angle stability; however, during unbalanced grid faults, IEEE Std. 2800-2022 requires IBRs to inject both positive- and negative-sequence reactive current. Enforcing compliance with this standard could compromise the stability of GFM IBRs under such fault conditions. This paper presents a preliminary transient stability study focused on the power angle stability of GFM IBRs operating in compliance with IEEE Std. 2800 during unbalanced faults. The goal is to assess potential stability issues associated with the standard's current injection requirements under fault ride-through conditions. The results show that injecting positive-sequence current with d-axis priority during unbalanced faults better preserves the power angle stability than the q-axis priority while still enabling negative-sequence current injection. These findings suggest that, to ensure stability, GFM IBRs might need to partially comply with IEEE Std. 2800 by prioritizing positive-sequence current injection along the d-axis.

14 SOLAR ENERGY↗
DOE OSTI2025

Field Testing of PID-p Susceptible Bifacial PERC Modules: Impact of Light, Voltage and Module History ​

This work investigates the potential induced degradation-polarization (PID-p) of bifacial passivated emitter and rear contact (PERC) modules installed in the field at the Florida Solar Energy Center. 22 modules were stressed over 1 year under various voltage (-1500V, -3500, +1500V) and mounting configurations (close to ground, 2 meters from ground, close to roof). The positively stressed modules were anticipated to have experiences PID-p on their front side. However, no degradation was observed, as the light-induced recovery effect effectively counteracted the degradation. The negatively stressed modules experienced Pmax drops during 2 weeks before stabilizing at 5-6% loss. I-V and EL characteristics suggest a PID-p degradation on the rear side. Lower degradation rates are observed with lower voltage and when the mounting configuration allows more albedo light on the rear side to compensate for the degradation. PID-p is observed to stabilize at similar level for the voltage and mounting configuration tested with slightly lower Pmax in winter. EL imaging reveals that cells are not degrading at the same rate across a module. Some cells get darker and then brighter which corresponds to the silicon/passivation interface going through depletion and then inversion when enough positive charges are accumulated. After full light-recovery, the modules were tested again along with 22 brand-new ones to assess the impact of the module history. Results confirmed the trends observed in the first year with PID-p occurring at voltage as low as -600V and recovered modules degrading faster than brand-new ones.

14 SOLAR ENERGY↗
DOE OSTI2025

Toward 100% Renewable Power Grids: A Review

The transition to a 100% renewable power grid remains beset by significant technical challenges. This paper critically examines the obstacles arising from the variability and unpredictability of renewable energy sources (RES), which complicate the real-time balancing of power generation and load demand. In addition to traditional stability concerns (e.g., rotor angle, voltage, and frequency stability), the increasing penetration of inverter-based resources (IBRs) introduces novel challenges, including resonance stability issues and converter-driven dynamics. Moreover, the dynamic behavior and fault response of IBRs diverge markedly from those of conventional synchronous generators, rendering traditional protection schemes increasingly inadequate. This paper reviews state-of-the-art solutions in power balancing, grid flexibility, stability enhancement, and advanced protection strategies, discussing their implications for future grid design. The analysis provides a comprehensive assessment of recent technological advancements, thereby outlining critical research directions essential for achieving a resilient, 100% renewable power grid.

100% renewable power grid↗
DOE OSTI2024

Effects of open circuit immersion and vertex potential on potentiodynamic polarization scans of metallic biomaterials

Abstract Electrodes made of commercially pure titanium (CP-Ti) and a CoCrMo alloy are immersed at an open circuit in a phosphate buffer saline electrolyte at room temperature for different durations prior to electrochemical analyses. Open circuit potential measurements, electrochemical impedance spectroscopy measurements, and cyclic potentiodynamic polarization (CPP) scans are used to assess the impact of the immersion time on derived property values. Stable passivation layers formed on both materials during immersion. The corrosion potentials determined from the anodic legs of CPP scans become more cathodic, and the corrosion currents decrease to lower values after longer immersion times. Measured currents indicate the layers formed on CP-Ti stabilize during forward anodic scans and persist to the vertex potential, whereas passivation breakdown occurs during anodic scans with CoCrMo with active corrosion at voltages up to the vertex potential. The characteristics of the return cathodic legs of CPP scans represent the surface conditions at the vertex potential: characteristic corrosion property values derived from the test responses represent passive surfaces on CP-Ti and leached surfaces on CoCrMo rather than intrinsic properties of those materials.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Quantifying System Strength From Grid-Forming Resources Using Frequency Scan Approach: Preprint

Current industry practices for quantifying the system strength contribution from grid-forming (GFM) resources to ensure stability of power systems dominated by inverter-based resources (IBRs) are primarily based on iterative electromagnetic transient (EMT) time-domain simulation studies. While feasible, these approaches are resource-intensive, lack scalability and intuition, and might not evaluate the system strength contribution over the entire frequency range of interest. This paper introduces a novel, frequency-domain approach to quantify system strength support provided by a GFM resource using frequency scans. The proposed method uses transfer functions from the grid voltage magnitude (V) and phase (?), respectively, to the reactive (Q) and active power (P) output of a GFM resource for quantifying its contribution to system strength. These transfer functions provide a direct measure of the ability of a GFM resource to behave as a stiff voltage source behind a reactance over a specified frequency range, enabling robust quantification of its system strength contribution. The key innovation of this work is the development of a frequency domain system strength metric called the dynamic short-circuit ratio (dSCR) that is suitable for IBR-dominated power systems and is directly related with the familiar short circuit ratio (SCR) metric. The new metric, dSCR, enables the assessment of system strength contributions from both synchronous machines and converter-based GFM resources using a unified benchmark, which is not possible with the traditional SCR metric. The paper also demonstrates how impedance scans could identify if an unstable condition observed during weak grid conditions is a result of the lack active or reactive power support or both. By leveraging the proposed frequency-domain dSCR metric for quantifying system strength contribution from GFM IBRs, the paper demonstrates targeted mitigation strategies for weak grid instabilities without resorting to repeated, time-consuming time-domain simulations. The result is a scalable and efficient approach to remediate stability challenges in power systems with high shares of IBRs and accelerating the integration of GFM technologies for system strength support in power systems.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS2010

Characterization of Low Noise, Precision Voltage Reference REF5025-HT Under Extreme Temperatures

The performance of Texas Instruments precision voltage reference REF5025-HT was assessed under extreme temperatures. This low noise, 2.5 V output chip is suitable for use in high temperature down-hole drilling applications, but no data existed on its performance at cryogenic temperatures. The device was characterized in terms of output voltage and supply current at different input voltage levels as a function of temperature between +210 C and -190 C. Line and load regulation characteristics were also established at six load levels and at different temperatures. Restart capability at extreme temperatures and the effects of thermal cycling, covering the test temperature range, on its operation and stability were also investigated. Under no load condition, the voltage reference chip exhibited good stability in its output over the temperature range of -50 C to +200 C. Outside that temperature range, output voltage did change as temperature was changed. For example, at the extreme temperatures of +210 C and - 190 C, the output level dropped to 2.43 V and 2.32 V, respectively as compared to the nominal value of 2.5 V. At cryogenic test temperatures of -100 C and -150 C the output voltage dropped by about 20%. The quiescent supply current of the voltage reference varied slightly with temperature but remained close to its specified value. In terms of line regulation, the device exhibited excellent stability between -50 C and +150 C over the entire input voltage range and load levels. At the other test temperatures, however, while line regulation became poor at cryogenic temperatures of -100 C and below, it suffered slight degradation at the extreme high temperature but only at the high load level of 10 mA. The voltage reference also exhibited very good load regulation with temperature down to -100 C, but its output dropped sharply at +210 C only at the heavy load of 10 mA. The semiconductor chip was able restart at the extreme temperatures of -190 C and +210 C, and the limited thermal cycling did not influence its characteristics and had no impact on its packaging as no structural or physical damage was observed.

Patterson, Richard↗
NASA NTRS1991

Assessment of a prototype sunphotometer for network applications, phase 1

Data taken in Tucson, AZ, for comparing the CE sunphotometer's results against the Univ. of Arizona's no. 3 solar radiometer are in very good agreement. The spectral voltage intercepts obtained on 15 different days taken with the CE instrument during a seven week period are stable and follow the same daily trends as the voltage intercepts for similar wavelengths contained in the Univ. of Arizona's no. 3 radiometer. The spectral optical depths obtained from both instruments are also in very good agreement and follow the same trends. The only problem that exists in the CE instrument does not have a heater to stabilize the detector temperature which is important around 1000 nm. Zenith sky radiance scans are in good agreement, but both instruments are biased by direct solar rays entering the instrument's respective entrance apertures. All diffuse light data shown were, therefore, taken with the instruments shielded from the direct sun. The CE sunphotometer results pertaining to the water vapor wavelength's are also in good agreement with the Univ. of Arizona's no. 3 and should prove useful for water vapor retrieval.

Reagan, J. A.↗
NASA NTRS1977

Photovoltaic, gravitationally-stabilized solid-state, satellite solar power station /GSS4PS/

The salient feature of a gravitationally-stabilized satellite solar power system (SSPS) for a photovoltaic system is that the large solar array is separated into smaller segments or subunits, joined together in a linear array oriented along the local vertical. Applicability of gravitational stabilization to the design of photovoltaic SSPS is demonstrated. Both actively controlled systems using multiple solar panels oriented to the sun and passively controlled systems requiring no sun orientation are considered and determined to be feasible. Expressions for gravity-gradient induced tension and restoring torques about the local vertical are assessed. Particular attention is directed to the applicability of solid-state approaches to the design of SSPS. It is shown that an all solid-state SSPS utilizing the LITOMIC (light-to-microwave conversion) concept is feasible but that a hybrid system employing a combination of both solid-state and cryogenic cooled low-voltage techniques to the design of the power management and distribution subsystem may also provide a solution.

Cantafio, L. J.↗
DOE OSTI2025

Performance assessment after long-term irradiation of ATLAS Micromegas detectors using 120 GeV muons at the Gamma Irradiation Facility at CERN

The ATLAS muon spectrometer will face an increased particle rate as a result of the increased instantaneous luminosity expected during the High-Luminosity LHC (HL-LHC) upgrade. The HL-LHC will provide a luminosity of $\mathscr{L}$ = 7.5 × 10 34 cm −2 s −1 and 3000 fb −1 of integrated luminosity in 10 years, about 9 times more data of the ones so far collected by the ATLAS experiment. Micromegas chambers are used in the New Small Wheel(s), the first forward muon spectrometer station, to provide tracking and triggering at the intense particle rates expected. The detectors are operated with a ternary gas mixture composed of Ar + 5%CO 2 + 2%iC 4 H 10 , providing good high voltage stability and a large pulse height, important for inclined track reconstruction of particles crossing the detector. To ensure the long-term stable operation of the detector during the whole HL-LHC period, and due to the hydrocarbon content in the mixture, an extensive aging campaign has been ongoing since 2021 at the CERN Gamma Irradiation Facility, where spare production chambers are long-term exposed to a 14 TBq 137 Cs 𝛾-source, accumulating so far, a charge equivalent to five years of HL-LHC operations under the highest expected background rate. This paper describes the results of the Micromegas chamber performance studies after two years of gamma irradiation and using the SPS/H4 120 GeV muon beams at CERN.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Impedance Scan of Inverter-Based Resources and Diesel Generator for Stability Analysis

Impedance-based methods are widely used for power system stability analysis with inverter-based resources (IBRs), e.g., assessing dynamic interactions between the power grid and an IBR, control interactions between multiple IBRs, and the sub-synchronous oscillation and damping phenomenon. Since it is difficult to get a numerical model 100% matching with the hardware IBR, using the hardware inverter directly to obtain its output impedance has become a prominent approach nowadays. Therefore, this article presents the impedance scan using hardware IBRs, and also a hardware diesel generator as it still stays with the grid before the grid completely goes to renewable. The devices under test (DuTs) for the impedance scan includes two 3-..phi.., 480 V, 60 Hz commercial grid-forming IBRs (one of 250 kVA and another of 125 kVA rating) in series with ..delta..-Y transformers, one 3-..phi.., 480 V, 60 Hz commercial grid-following IBR (of 125 kVA rating), and a 3-..phi.., 480 V, 60 Hz commercial diesel generator (of 187.5 kVA rating). Using voltage signals perturbed with sub-, inter-, and higher harmonic components, and measuring the current response, the positive-sequence impedances are computed via an offline-based post-analysis. Moreover, best-fit transfer functions are estimated that closely resemble the measured data points of the positive-sequence impedances. Based on the observations from various outcomes of the hardware experiments, this article also provides some fundamental insights on the equivalent positive-sequence impedance of a combination of multiple hardware components by comparing the estimated and the empirically computed impedances. A comparative insight on the damping capability of the DuTs using the positive-sequence impedances of the hardware is also discussed.

current measurement↗
DOE OSTI2023

Assessing the Intrinsic Roles of Key Dopant Elements in High–Nickel Layered Oxide Cathodes in Lithium–Based Batteries

A rational compositional design is critical for utilizing LiNiO 2 -based cathodes with Ni contents > 90% as promising next-generation cathode materials. Unfortunately, the lack of a fundamental understanding of the intrinsic roles of key elements, such as cobalt, manganese, and aluminum, makes the rational compositional design of high-Ni cathodes with a limited range of dopants (<10%) particularly challenging. Here, with 5% single-element doped cathodes, viz., LiNi 0.95 Co 0.05 O 2 , LiNi 0.95 Mn 0.05 O 2 , and LiNi 0.95 Al 0.05 O 2 , along with undoped LiNiO 2 (LNO), the influences of the dopants are systematically examined through a control of cutoff charge energy density and a common practice of cutoff charge voltage. Comprehensive investigations into the electrochemical properties, combined with in-depth analyses of the structural and interfasial stabilities and electrolyte decomposition pathways through advanced characterizations, unveil the following: i) the intrinsic role of dopants regulates the cathode energy density or state-of-charge and, more critically, the occurrence of H2–H3 phase transition, which essentially dictates cyclability; ii) undoped LNO can be stabilized well with the avoidance of H2–H3 phase transition; and iii) Co provides more merits overall with an optimized electrochemical operating condition. Finally, this work provides guidance for the compositional design of high-energy-density high-Ni cathodes and sheds light on the challenges of removing Co.

25 ENERGY STORAGE↗
DOE OSTI2025

Characterization of Impedance and Stability for Doubly-Fed Induction Generator Based on Voltage-Modulated Direct Power Control

Voltage-modulated direct power control (VM-DPC) applied to the doubly-fed induction generator (DFIG) offers superior steady-state and transient performance but remains underexplored for suppressing wideband oscillations. Here, this article proposes a comprehensive impedance for the VM-DPC-based DFIG, analyzing its impedance characteristics and stability mechanisms compared with the DFIG based on vector-oriented control (VOC). The unified power transfer function is defined for DFIGs employing VM-DPC or VOC to ensure consistent comparison benchmarks. The comprehensive impedance of VM-DPC-based DFIG, incorporating mechanical and grid-side converter (GSC) dynamics, is derived using complex vector modeling in the αβ -frame. Furthermore, the influence of VM-DPC parameters and grid strength on the stability of grid-connected DFIG systems is assessed through eigenvalue trajectory analysis. Impedance analysis reveals the significant contributions of mechanical and GSC dynamics to DFIG impedance, as well as the narrower frequency range of negative resistance in the VM-DPC-based DFIG compared to the VOC-based DFIG. Stability analysis identifies the VM-DPC parameters of the rotor-side converter as dominant factors affecting system stability and confirms that the VM-DPC-based DFIG achieves better stability under weak grid conditions than its VOC-based counterpart. These findings are validated through simulations and experiments.

42 ENGINEERING↗
DOE OSTI2023

Maritime Fuel Cell Generator Project: 2018 – 2023

This report summarizes activity in the Maritime Fuel Cell (MarFC) Generator Project from 2018 – 2023. FY 2018 saw the implementation of upgrades and repairs, making the unit more reliable and operator friendly. In FY2019 the team engaged the Scripps Institution of Oceanography (SIO) to use the MarFC to provide zero-emission shore power to the research vessel R/V Robert Gordon Sproul while in port at the Nimitz Marine Facility in San Diego, CA. In FY2020, the MarFC unit was shipped to San Diego, CA. A fueling contract with IGX was established to support MarFC operations at SIO, with renewable hydrogen provided by the California State University Los Angeles (CSULA) hydrogen station. The project team (Sandia, Cummins/Hydrogenics) provided training to SIO staff on the technical details of the MarFC, the safe use of hydrogen in general and the MarFC in particular. The first fueling of the unit at the SIO pier was successfully completed by IGX. The first powering of a vessel with fuel-cell shore power was conducted with the R/V Robert Gordon Sproul. While the mechanical systems (lights, AC, ventilation, hydraulics, pumps and cranes) were powered without incident, problems arose when powering the computer systems. Inspections carried out in FY2021 revealed the MarFC needed routine maintenance. Maintenance was performed and the unit was upgraded. The MarFC was turned on after the year pause, and initial test data on power levels and stability were collected. FY2022 was a year spent repairing, upgrading and testing the MarFC unit. Spikes in power and voltage were observed above 60 kW that could potentially extend below 60 kW with time. Such spikes could cause problems with the Sproul electrical systems. These age-related problems, the extended time for the Sproul spent in dry dock for scheduled upgrades, and the associated need to reschedule the vessel’s high-priority science missions made it no longer possible to deploy the unit at SIO. After due consideration, the decision was made by DOE, MARAD and the project team to cease the deployment, remove the MarFC from SIO, and not pursue further deployment activities. On December 2, 2022, the MarFC unit was removed from the Scripps Nimitz Marine Facility and shipped to Fridley, Michigan. The Cummins/Hydrogenics plan for the unit is to assess the condition of the MarFC subcomponents, and then use it as a training/learning system for technical employees new to hydrogen fuel-cell technology. After summarizing project activity from 2018 – 2023, this report provides a review of lessons learned. This report provides next steps in contemplating a follow-on project that would further advance the use of fuel-cell-based shore power in a marine setting. A comparison is made of the project results to the original objectives. This report ends with an accounting of presentations stemming from the project, and a list of references.

08 HYDROGEN↗