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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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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Grid Forming Inverter: Laboratory-Scale Hardware Test Bed Setup and Weak Grid Operation

In recent times, the concept of grid forming inverters has gained popularity. Grid forming inverters have proven to be a promising alternative to the grid following inverters. In this paper, we present the hardware test bed implementation of grid forming inverter in islanding mode as well as in grid connected mode. The control structure includes inverter-level inner current control and outer voltage control, and plant-level P - f and Q - V droop control. The Q - V droop provides the voltage command, whereas P - f droop provides the frequency command and is also key for the synchronization process. While it is straightforward to set up the test bed for the islanded operation, it is a challenging process to set up the grid-forming inverter in the grid-connected mode. We present the key technologies and demonstrate the start-up process and weak grid operation using the hardware experiment results. Results from EMT model developed in MATLAB/SimPowerSystems are also presented for side-by-side comparison.

Mittal, Ratik↗
DOE OSTI2024

Performance Evaluation of Multi-Vendor Grid-Forming Inverters for Grid-Connected Operation Through Hardware Experimentation: Preprint

Existing real-world projects of GFM inverters that operate in parallel to power grids typically are sized between dozens and a few hundreds Megawatt (MW) scale according to a recent NERC GFM inverter white paper. These large systems are often difficult to evaluate prior to deployments because of their large size. The performance of smaller GFM inverters (dozens to a few hundreds MW) that operate parallel with power grids (distribution systems) is even less understood. There is an opportunity to better understand these systems through hardware testing under controlled laboratory conditions. Therefore, this paper presents the functional performance evaluation tests of multiple (three) commercial GFM inverters when they operate in parallel with the grid through hardware experiments. The goal of these tests is to explore the GFM inverters' functionalities and dynamic response when in parallel with power grids to eventually develop universal specifications for GFM inverters. Both steady state (changing the inverter's frequency and voltage droop) and transient (adding step change in grid's frequency/voltage) tests are performed for each GFM inverter with the same testing circuit and testing protocol. The experimental results indicate the bench-marked performance that: 1) the GFM inverters can be dispatched through frequency and voltage droop intercepts to output the target power when paralleled to the grid; 2) the GFM inverters automatically respond to system frequency and voltage events to output the needed power, however, the GFM inverters all show stability issues when absorbing reactive power from the grid.

grid-forming inverters↗
DOE OSTI2026

Small-Signal Analysis of Current-Limiting Grid-Forming Inverters

Grid-forming (GFM) inverters are equipped with a current limiter to protect the device during grid disturbances. Because the intervention of the current limiter can compromise the transient stability of the GFM inverter, various types of current limiter designs and additional frequency-stabilization control methods have been proposed in recent literature to aid in transient GFM inverter stability; however, the small-signal stability implications of adding these additional control blocks during, in particular, off-nominal conditions are not fully understood. To address this challenge, this paper presents a generic small-signal model of a GFM inverter that incorporates various types of current limiters and frequency stability-enhancing controls. With the proposed model, we analyze the root causes of inverter instability, which reveals two critical design trade-offs. First, due to current-limiter engagement caused by a disturbance, the GFM inverter dynamics are altered, which can lead to voltage oscillations. Second, additional frequency-stabilization controls can improve the small-signal stability of the GFM inverter, but at the cost of reduced power and voltage support to the grid. Comprehensive hardware experiments validate the theoretical concept and analysis. The findings in this work underscore the importance of incorporating both transient-response and small-signal dynamics requirements into the design procedure of GFM current limiters and frequency-stabilization controls.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2023

Seamless Transition of Critical Infrastructures using Droop Controlled Grid-forming Inverters

Seamless recovery of power to critical infrastructures, after grid failure, is a crucial need arising in scenarios that are increasingly becoming more frequent. Here, this article proposes a seamless transition strategy using a single and unified mode-dependent droop controlled grid-forming inverters. The control strategy achieves the following objectives: 1) regulates the output active and reactive power by the droop-controlled inverters to a desired value while operating in on-grid mode; 2) seamless transition and recovery of power injections into the load after grid failure by inverters that operates in grid-forming mode all the time; 3) requires only a single bit of information on the grid/network status for the mode transition. A framework for assessing the stability of the system and to guide the choice of parameters for controllers is developed using control-oriented modeling. A controller hardware-in-the-loop-based real-time simulation study on a test system based on the realistic electrical network of a commercial-scale medical center is conducted for initial prototyping of the control strategy. A hardware experiment is conducted with two 3 - $\phi$, 480 -V, 125 -kVA grid-forming inverters, a 3 - $\phi$, 480 -V, 270 -kVA grid simulator, a physical grid switch, and a physical load bank. The experimental data establishes the effectiveness of the always grid-forming operation and control of inverters in meeting power delivery objectives when on-grid and off-grid under various kinds of loads and scenarios while minimizing transients during transitions. Furthermore, performance comparison with existing strategies showcases the advantage of the proposed strategy.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2023

Model-Based Detection Scheme for Spoofed Sensor Data in Grid-Connected Inverters

In this article, a novel method to detect spoofed sensor data (SSD) for grid-connected inverters is proposed. First, a Kalman filter is used to estimate the inverter status in the proposed method. Then, the impact of SSD on the residual between estimation and control reference is analyzed. By leveraging the standard error of residual, an adaptive cumulative sum (CUSUM) chart is developed to achieve fast SSD detection and improve robustness. In addition, the proposed SSD detection method is verified by the hardware experiment. A comparative experiment with a conventional method also demonstrates the rapidity and robustness of the proposed method. Lastly, the performance of the proposed method under different noise covariance matrices is analyzed. Comprehensive analysis shows that the proposed method meets the detection requirement in IEEE 1547 Standard.

42 ENGINEERING↗
DOE OSTI2022

Laminated Permanent Magnets Enable Compact Magnetic Components in Current-Source Converters

Magnetic components have become one of the primary barriers to high power density converters, especially to current-source converters (CSCs). In CSCs, the inductors/transformers have a predominantly dc flux to store energy, which can be offset by standard permanent magnets (PMs). However, eddy currents in standard PMs induce significant losses and thermal stress for medium-frequency applications. This article proposes using laminated PMs to offset the dc flux while reducing eddy currents, leading to significant reductions in the size, cost, and losses of inductors/transformers. Furthermore, the laminated PMs’ optimal location, orientation, and distribution are investigated to generalize this approach for maximum benefits. Here, three-dimensional finite-element analysis simulation and hardware experiments are presented to validate the effectiveness of the proposed approach in a medium-frequency transformer (MFT) for CSCs. Compared with standard PMs, the proposed use of laminated PMs reduces aggregate core-plus-PM losses by 85% in experiments, and thus, relaxes the MFT thermal design. Finally, the proposed approach is experimentally validated in a 40 kVA flyback-type MFT for a soft-switching solid-state transformer. Compared to the traditional design without any PMs, the proposed design increases the saturation current by 46% while inducing only 5% more losses, leading to significant savings in magnetics cost and size.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2022

Virtual Dynamic Grid Impedance and Its Impacts on Harmonics and Stability of Inverter Based Resources Plant

Nowadays, a large number of inverter-based resources (IBRs) are integrated into the grid at a single connection point as an IBR plant. In this article, a virtual dynamic grid impedance concept is introduced to evaluate the harmonics and stability for grid integration of an IBR plant containing multiple IBRs. First, a detailed theoretical study is conducted to build a foundation of the virtual grid impedance concept, which is a dynamic impedance that changes with the number of IBRs added into an IBR plant. Then, based on the new virtual dynamic grid impedance concept, frequency spectrum analysis is performed to explore harmonic impact at the interconnection point for an IBR plant with IBRs having L, LC, and LCL filters, respectively. An electromagnetic transient (EMT) simulation model of a grid-connected IBR plant is developed to explore the harmonics and stability of the IBR plant connected to the grid as well as the reliable operation of IBRs within the plant from the novel virtual equivalent dynamic grid impedance point of view. Hardware experiments are conducted to validate the EMT simulation evaluation. The results show that the number of IBRs added into an IBR plant influences the grid impedance, i.e., grid strength, and the grid impedance variation has multiple impacts on the IBR plant and IBRs within the plant depending on the grid-connected filters of the IBRs.

grid impedance↗
DOE OSTI2026

Small Hydro Power Plants with Integrated BESS for Enhance Resiliency

Battery energy storage systems (BESS) are an important asset for power systems with high integration levels of renewable energy, and they can be controlled to provide various services to the grid. This paper presents the hardware demonstration and characterization of using a utility-scale BESS with grid-following (GFL) and grid-forming (GFM) controls and a run-of-river (ROR) hydropower plant to perform a bottom-up power system black start that enhances power systems' resiliency. ROR hydropower plants are generally not used for power system restoration due to their frequency instability during islanded operation; however, BESS with droop control can provide critical damping to convert a ROR hydropower generator into a black start- capable unit. To demonstrate this, we carry out hardware experiments at the megawatt-scale integrating a synchronous generator driven by a dynamometer, an actual GFL/GFM BESS, a medium-voltage impedance network, and a load bank. The demonstration shows the different roles of BESS with GFL and GFM control in power system restoration. GFL BESS can suffer from high-frequency oscillations, even instability, depending on the droop control gain and loading condition. The results provide further insights for system operators on how GFL- or GFM controlled BESS can enhance grid stability and how hydro-BESS hybrids can operate as a black-start-capable unit. The presented experimental results are also a valuable resource to understand the different stability characteristics of real-world BESS with different control modes.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS1972

Manned versus unmanned space-based astronomy.

Discussion of the pros and cons of manned and unmanned space-based astronomical observatory systems. Rather than compete with one another, manned and unmanned systems, it is felt, should complement themselves mutually. The paramount factor inhibiting the growth of both manned and unmanned systems is shown to be the high cost per pound of payload equipment. The main hope for reducing this cost is the advent of a space station or shuttle sortie mode of operation in which the frequency of flights will reduce the necessity to guarantee experiment success. This, in turn, should reduce the complexity of experiment management and the cost of experiment hardware.

Henize, K. G.↗
NASA NTRS1973

A contaminant monitor for submarine atmospheres.

A requirement for monitoring selected atmospheric constituents on board nuclear powered submarines has been met by the development of the Central Atmosphere Monitoring System, Mark I. This system employs a mass spectrometer to monitor H2, H2O, N2, O2, CO2, Freon 11, Freon 12, and Freon 114, in addition to an infrared sensor for CO. The CAMS MKI development is discussed, including background, operating fundamentals, principal requirements, functional and physical descriptions, and summarized test results. Each of two prototype units has successfully completed over 9000 hr of operational sea trails, providing the necessary ground work for the manufacture of production units. At the same time, these units, which have benefited extensively from NASA hardware experience, may in turn provide useful data for the development of a new class of maintainable atmospheric monitoring instrumentation for manned spacecraft.

Ruecker, M. R.↗
NASA NTRS1973

Skylab medical experiments altitude test crew observations.

The paper deals with the crew's observations during training and the SMEAT 56-day test. Topics covered include the crew's adaptation to the SMEAT environment and medical experiments protocol. Personal observations are made of daily activities surrounding the medical experiments hardware, Skylab clothing, supplementary activities, recreational equipment, food, and waste management. An assessment of these items and their contributions to the Skylab flight program is made.

Bobko, K. J.↗
NASA NTRS1974

Skylab medical operational support

To support the medical research and the maintenance of crew health during the three Skylab missions, a medical operational support team was organized. The functions of this team ranged from medical data management to medical systems engineering monitoring during the flights. The capability to expand preflight and postflight medical research and analysis was supplied through the use of the Skylab mobile laboratories. These mobile laboratories were not only capable of being transported to the recovery ship for postflight use, but also served as a preflight test area for gathering crewman baseline data. The laboratories contained experiment hardware identical to that of the flight orbital workshop and a laboratory diagnostic facility that duplicated many of the capabilities of ground-based clinical laboratories.

Primeaux, G. R.↗
NASA NTRS1975

Evaluation of boron/aluminum tubes in compression

A brief analytical and experimental investigation was conducted to determine the compressive behavior of a limited number of boron/aluminum (B/Al) tubes. The purpose of the investigation was to gain hardware experience in a limited evaluation of the material for possible application to spacecraft truss structures. Specimen description, test procedures and results are presented as well as comparisons with theoretical predictions regarding local column stability. It is shown that the experimental results of full-scale tests are consistent with previously reported data and that the local stability of B/Al columns as determined through short column tests can best be predicted using large deflection theory.

Knoell, A. C.↗
NASA NTRS1975

Apollo Soyuz, mission evaluation report

The Apollo Soyuz mission was the first manned space flight to be conducted jointly by two nations - the United States and the Union of Soviet Socialist Republics. The primary purpose of the mission was to test systems for rendezvous and docking of manned spacecraft that would be suitable for use as a standard international system, and to demonstrate crew transfer between spacecraft. The secondary purpose was to conduct a program of scientific and applications experimentation. With minor modifications, the Apollo and Soyuz spacecraft were like those flown on previous missions. However, a new module was built specifically for this mission - the docking module. It served as an airlock for crew transfer and as a structural base for the docking mechanism that interfaced with a similar mechanism on the Soyuz orbital module. The postflight evaluation of the performance of the docking system and docking module, as well as the overall performance of the Apollo spacecraft and experiments is presented. In addition, the mission is evaluated from the viewpoints of the flight crew, ground support operations, and biomedical operations. Descriptions of the docking mechanism, docking module, crew equipment and experiment hardware are given.

Source record↗
NASA NTRS1977

Finite Element Stability Analysis for Coupled Rotor and Support Systems

The effects of fuselage motions on stability and random response were analytically assessed. The feasibility of adequate perturbation models from non-linear trim conditions was studied by computer and hardware experiments. Rotor wake-blade interactions were assessed by using a 4-bladed rotor model with the capability of progressing and regressing blade pitch excitation (cyclic pitch stirring), by using a 4-bladed rotor model with hub tilt stirring, and by testing rotor models in sinusoidal up or side flow.

Hohenemser, K. H.↗
NASA NTRS1978

Effects of exercise and excitement on mesenteric and renal dynamics in conscious, unrestrained baboons

Radiotelemetry was used to measure arterial pressure and mesenteric and renal blood flows from nine unrestrained, conscious baboons during periods of rest, moderate exercise, and extreme excitement. A description of the experiments hardware is presented, including artificial depressants phenylcyclidine hydrochloride, 0.5-1.0 mg/kg, and pentobarbital sodium, 15 mg/kg, and an ultrasonic telemetry flow meter. Results showed rising heart rate and arterial pressure coupled with a reduction of mesenteric and renal flows as the level of exercise was increased. These findings are compared with mesenteric and renal flows somewhat above control level, but relatively stable heart rate and arterial pressure, postprandially. Attention is given to a quantitative analysis of the experimental results.

Vatner, S. F.↗
NASA NTRS1980

Nighttime/daytime optical survey of lightning and convective phenomena experiment (NOSL)

The Nighttime/Daytime Optical Survey of Lightning experiment was selected for flight on Orbital Flight Test 2 of the Space Shuttle. The background and rationale for the experiment are presented and the experiment hardware, the operating procedures, and the data analysis technique are discussed. Some preliminary results from the prototype hardware development are also presented.

Vonnegut, B.↗
NASA NTRS1982

OSO-8 soft X-ray wheel experiment: Data analysis

The soft X-ray experiment hardware and its operation are described. The device included six X-ray proportional counters, two of which, numbers 1 and 4, were pressurized with on-board methane gas supplies. Number 4 developed an excessive leak rate early in the mission and was turned off on 1975 day number 282 except for brief (typically 2-hour) periods up to day 585 after which it as left off. Counter 1 worked satisfactorily until 1975 day number 1095 (January 1, 1978) at which time the on-board methane supply was depleted. The other four counters were sealed and all except number 3 worked satisfactorily throughout the mission which terminated with permanent satellie shut-down on day 1369. This was the first large area thin-window, gas-flow X-ray detector to be flown in orbit. The background problems were severe and consumed a very large portion of the data analysis effort. These background problems were associated with the Earth's trapped electron belts.

Kraushaar, W. L.↗