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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 73 records · Page 4

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NASA NTRS1993

Study of switching transients in high frequency converters

As the semiconductor technologies progress rapidly, the power densities and switching frequencies of many power devices are improved. With the existing technology, high frequency power systems become possible. Use of such a system is advantageous in many aspects. A high frequency ac source is used as the direct input to an ac/ac pulse-density-modulation (PDM) converter. This converter is a new concept which employs zero voltage switching techniques. However, the development of this converter is still in its infancy stage. There are problems associated with this converter such as a high on-voltage drop, switching transients, and zero-crossing detecting. Considering these problems, the switching speed and power handling capabilities of the MOS-Controlled Thyristor (MCT) makes the device the most promising candidate for this application. A complete insight of component considerations for building an ac/ac PDM converter for a high frequency power system is addressed. A power device review is first presented. The ac/ac PDM converter requires switches that can conduct bi-directional current and block bi-directional voltage. These bi-directional switches can be constructed using existing power devices. Different bi-directional switches for the converter are investigated. Detailed experimental studies of the characteristics of the MCT under hard switching and zero-voltage switching are also presented. One disadvantage of an ac/ac converter is that turn-on and turn-off of the switches has to be completed instantaneously when the ac source is at zero voltage. Otherwise shoot-through current or voltage spikes can occur which can be hazardous to the devices. In order for the devices to switch softly in the safe operating area even under non-ideal cases, a unique snubber circuit is used in each bi-directional switch. Detailed theory and experimental results for circuits using these snubbers are presented. A current regulated ac/ac PDM converter built using MCT's and IGBT's is evaluated.

Zinger, Donald S.↗

NASA NTRS1974

Load insensitive electrical device

A class of power converters is described for supplying direct current at one voltage from a source at another voltage. It includes a simple passive circuit arrangement of solid-state switches, inductors, and capacitors by which the output voltage of the converter tends to remain constant in spite of changes in load. The switches are sensitive to the current flowing in the circuit and are employed to permit the charging of capacitance devices in accordance with the load requirements. Because solid-state switches (such as SCR's) may be used with relatively high voltage and because of the inherent efficiency of the invention that permits relatively high switching frequencies, power supplies built in accordance with the invention, together with their associated cabling, can be substantially lighter in weight for a given output power level and efficiency of operation than systems of the prior art.

Schwarz, F. C.↗

NASA NTRS1977

Phase substitution of spare converter for a failed one of parallel phase staggered converters

Failure detection and substitution of a spare module is provided in a system having a plurality of phase staggered modules connected in parallel to deliver regulated voltage from an unregulated source. Phase control signals applied to the active converter modules are applied to the spare module through NOR gates associated with and disabled by the power output of respective modules such that failure of any one enables its phase control signal to be applied to the spare module, thus controlling the spare module to operate in the phase position of the failed module. A NAND gate detects when any one active module fails and enables a gate in the spare module, thus activating the spare module.

Mclyman, W. T.↗

DOE OSTI2022

Time series anomaly detection in power electronics signals with recurrent and ConvLSTM autoencoders

The anomalies in the high voltage converter modulator (HVCM) remain a major down time for the spallation neutron source facility, that delivers the most intense neutron beam in the world for scientific materials research. In this work, we propose neural network architectures based on Recurrent AutoEncoders (RAE) to detect anomalies ahead of time in the power signals coming from the HVCM. Bi-directional gated recurrent unit, bi-directional long-short term memory (LSTM), and convolutional LSTM (ConvLSTM) are developed, trained, and tested using real experimental signals from the HVCM module. The results show a good performance of the proposed RAE models, achieving precision up to 91%, recall up to 88%, false omission rate as low as 20% (i.e. 80% of the anomalies were detected), and area under the ROC curve up to 0.9. The three RAE models provide very comparable performance, with LSTM showing slightly better performance than GRU and ConvLSTM. The RAE models are benchmarked against other anomaly detection methods, including isolation forest, support vector machine, local outlier factor, feedforward and convolutional autoencoders, and others; showing a better performance. Here, the results of this study demonstrate the promising potential of RAE in anomaly detection for real-world power systems, and for increasing the reliability of the HVCM modules in the spallation neutron source.

42 ENGINEERING↗

NASA NTRS1991

System and component design and test of a 10 hp, 18,000 rpm AC dynamometer utilizing a high frequency AC voltage link, part 1

Hard and soft switching test results conducted with one of the samples of first generation MOS-controlled thyristor (MCTs) and similar test results with several different samples of second generation MCT's are reported. A simple chopper circuit is used to investigate the basic switching characteristics of MCT under hard switching and various types of resonant circuits are used to determine soft switching characteristics of MCT under both zero voltage and zero current switching. Next, operation principles of a pulse density modulated converter (PDMC) for three phase (3F) to 3F two-step power conversion via parallel resonant high frequency (HF) AC link are reviewed. The details for the selection of power switches and other power components required for the construction of the power circuit for the second generation 3F to 3F converter system are discussed. The problems encountered in the first generation system are considered. Design and performance of the first generation 3F to 3F power converter system and field oriented induction moter drive based upon a 3 kVA, 20 kHz parallel resonant HF AC link are described. Low harmonic current at the input and output, unity power factor operation of input, and bidirectional flow capability of the system are shown via both computer and experimental results. The work completed on the construction and testing of the second generation converter and field oriented induction motor drive based upon specifications for a 10 hp squirrel cage dynamometer and a 20 kHz parallel resonant HF AC link is discussed. The induction machine is designed to deliver 10 hp or 7.46 kW when operated as an AC-dynamo with power fed back to the source through the converter. Results presented reveal that the proposed power level requires additional energy storage elements to overcome difficulties with a peak link voltage variation problem that limits reaching to the desired power level. The power level test of the second generation converter after the addition of extra energy storage elements to the HF link are described. The importance of the source voltage level to achieve a better current regulation for the source side PDMC is also briefly discussed. The power levels achieved in the motoring mode of operation show that the proposed power levels achieved in the generating mode of operation can also be easily achieved provided that no mechanical speed limitation were present to drive the induction machine at the proposed power level.

Lipo, Thomas A.↗

NASA NTRS1987

A study of Schwarz converters for nuclear powered spacecraft

High power space systems which use low dc voltage, high current sources such as thermoelectric generators, will most likely require high voltage conversion for transmission purposes. This study considers the use of the Schwarz resonant converter for use as the basic building block to accomplish this low-to-high voltage conversion for either a dc or an ac spacecraft bus. The Schwarz converter has the important assets of both inherent fault tolerance and resonant operation; parallel operation in modular form is possible. A regulated dc spacecraft bus requires only a single stage converter while a constant frequency ac bus requires a cascaded Schwarz converter configuration. If the power system requires constant output power from the dc generator, then a second converter is required to route unneeded power to a ballast load.

Stuart, Thomas A.↗

NASA NTRS1987

A study of Schwarz converters for nuclear powered spacecraft

Stuart, Thomas A.↗

DOE OSTI2024

Distance preserving machine learning for uncertainty aware accelerator capacitance predictions

Abstract Accurate uncertainty estimations are essential for producing reliable machine learning models, especially in safety-critical applications such as accelerator systems. Gaussian process models are generally regarded as the gold standard for this task; however, they can struggle with large, high-dimensional datasets. Combining deep neural networks with Gaussian process approximation techniques has shown promising results, but dimensionality reduction through standard deep neural network layers is not guaranteed to maintain the distance information necessary for Gaussian process models. We build on previous work by comparing the use of the singular value decomposition against a spectral-normalized dense layer as a feature extractor for a deep neural Gaussian process approximation model and apply it to a capacitance prediction problem for the High Voltage Converter Modulators in the Oak Ridge Spallation Neutron Source. Our model shows improved distance preservation and predicts in-distribution capacitance values with less than 1% error.

43 PARTICLE ACCELERATORS↗

DOE OSTI2024

Machine Learning-Assisted Stability Boundary Determination of Multiport Autonomous Reconfigurable Solar Power Plants

The multiport autonomous reconfigurable solar (MARS) power plant is a promising solution to integrate renewable resources and energy storage systems into the alternating current (ac) power grid and an high-voltage direct current (HVdc) link. In the MARS system, various input power sources are connected to the individual submodules (SMs) through direct current (dc)–dc converters. However, the presence of external power sources can result in unbalanced capacitor voltages of SMs, thereby violating stability constraints under multiple/diverse operating conditions. This article aims to address the gap by accurately determining the stability boundary of the MARS system. As such, a novel machine learning (ML)-assisted energy balancing control (EBC) criterion is proposed. Further, in conjunction with a refined EBC, this approach ensures balanced capacitor voltages across various types of SMs, significantly enhancing the overall system efficiency. The proposed EBC criterion effectively controls EBC activation and deactivation, achieving remarkable accuracy. Both power systems computer aided design (PSCAD)/electromagnetic transients including direct current (EMTDC) simulations and control hardware-in-the-loop (cHIL) tests are conducted to validate the feasibility and efficiency of the proposed method. By combining the EBC and ML-assisted EBC criterion, efficient energy management is achieved for systems featuring multiple input power sources, such as MARS. This approach enables the system to fully exploit its potential across an expanded operational range while upholding high-efficiency standards.

14 SOLAR ENERGY↗

DOE OSTI2021

Preventing Voltage Divergence in Series-Stacked Bidirectional Battery Energy Storage DC-DC Converter under Asymmetrical Operating Conditions

DC stacked topologies have gained popularity for interfacing individual photovoltaic panels to a high-voltage DC bus. A similar approach can be used to interface individual battery packs to the same DC bus, which allows active balancing of battery substrings and the use of lower voltage switches. Any imbalance in battery current, however, can cause the converter output voltages to diverge. This paper describes the source of voltage divergence and demonstrates a solution that allows seamless stacking of multiple battery packs to be interfaced to a high voltage DC bus. To prevent the voltage divergence phenomenon and allow asymmetrical battery charging for efficient battery state of charge management, the PI-based decentralized voltage control enabling both capacitor voltage sharing and asymmetrical capacitor voltage control is proposed. The effectiveness of the decentralized voltage control strategy is demonstrated through controller hardware-in-the-loop test results.

Kim, Namwon↗

NASA NTRS2001

A Step Response Based Mixed-Signal BIST Approach for Continuous-time Linear Circuits

A new Mixed-Signal Built-in self-test approach that is based upon the step response of a reconfigurable (or multifunction) analog block is presented in this paper. The technique requires the overlapping step response of the Circuit Under Test (CUT) for two circuit configurations. Each configuration can be realized by changing the topology of the CUT or by sampling two CUT nodes with differing step responses. The technique can effectively detect both soft and hard faults and does not require an analog-to-digital converter (ADC) and/or digital-to-analog converter(DAC). It also does not require any precision voltage sources or comparators. This approach does not require any additional analog circuits to realize the test signal generator and sample circuits. The paper is concluded with the application of the proposed approach to a circuit found in the work of Epstein et al and two ITC 97 analog benchmark circuits.

Walker, Alvernon↗

NASA NTRS2001

A Step Response Based Mixed-Signal BIST Approach

A new Mixed-Signal Built-in Self-test approach that is based upon the step response of a reconfigurable (or multifunction) analog block is presented in this paper. The technique requires the overlapping step response of the Circuit Under Test (CUT) for two circuit configurations. Each configuration can be realized by changing the topology of the CUT or by sampling two CUT nodes with differing step responses. The technique can effectively detect both soft and hard faults and does not require an analog-to-digital converter (ADC) and/or digital-to-analog converter( DAC). It also does not require any precision voltage sources or comparators. The approach does not require any additional analog circuits to realize the test signal generator and a two input analog multiplexer for CUT test node sampling. The paper is concluded with the application of the proposed approach to a circuit found in the work of Epstein et a1 and two ITC 97 analog benchmark circuits.

Walker, Alvernon↗

DOE OSTI2026

PowerConverterDynamics.jl

SAND2026-22944O PowerConverterDynamics.jl is a Julia software package for differentiable DC power-conversion dynamics. It models a variable DC source, power converter, common DC bus, and battery module with current, voltage, loss, and state-of-charge dynamics. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Michelen Strofer, Carlos [Sandia National Lab. (SN↗

DOE OSTI2023

SiC Based Modular Transformer-less MW-Scale Power Conditioning System and Control for Flexible CHP System

This project aims at developing a SiC-based, modular, transformer-less (60-Hz-transformers-free), MW-scale, four-wire DC/AC power conditioning system (PCS) converter, and a corresponding control system for flexible-CHP (F-CHP) systems. With the help of an F-CHP controller and power electronics converters, different CHP sources, renewable sources, and batteries can be assembled to the DC grid, which is then connected to the medium voltage (MV) AC grid through the PCS converter. To meet grid support and performance requirements, the F-CHP controller design and PCS converter design follow IEEE 1547 and IEEE 2030.7 standards. Five main tasks, including PCS converter design, F-CHP controller development, PCS converter prototype building and testing, F-CHP controller testing, and PCS paralleling, have been carried out. In this project, the F-CHP controller testing has been completed in simulation, HIL and HTB, and the PCS converter prototypes have been successfully built and tested.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2021

A Novel Decentralized PWM Interleaving Technique for Ripple Minimization in Series-Stacked DC-DC Converters

Cascaded dc-dc converters are commonly used in applications where distributed energy sources or loads are connected to elevated voltage levels for power transfer. In such systems, it is advantageous to minimize the ripple on the bus current and voltage by proper phase shifting of the pulse-width modulation (PWM) pulses among the converters via a method known as interleaving. Existing approaches use either a centralized controller or separate communication lines among the stacked converters to control their relative PWM switch transitions. The key drawbacks are that these methods entail significant wiring, the central controller acts as a single point of failure, and implementation on very large numbers of units is impractical. In this paper, we introduce a decentralized interleaving control (DIC) strategy that acts on local current measurements at every converter and achieves communication-free PWM interleaving among the series-stacked converters. The proposed controller is simple in structure and is shown to converge asymptotically to the interleaved state irrespective of clock drifts among the digital signal processors. Experimental results are provided for a system of five series-connected converters showing a 10× reduction in the current ripple compared to normal operation.

cascaded converter↗

DOE OSTI2021

A Novel Decentralized PWM Interleaving Technique for Ripple Minimization in Series-Stacked DC-DC Converters: Preprint

Cascaded dc-dc converters are commonly used in applications where distributed energy sources or loads are connected to elevated voltage levels for power transfer. In such systems, it is advantageous to minimize the ripple on the bus current and voltage by proper phase shifting of the pulse-width modulation (PWM) pulses among the converters via a method known as interleaving. Existing approaches use either a centralized controller or separate communication lines among the stacked converters to control their relative PWM switch transitions. The key drawbacks are that these methods entail significant wiring, the central controller acts as a single point of failure, and implementation on very large numbers of units is impractical. In this paper, we introduce a decentralized interleaving control (DIC) strategy that acts on local current measurements at every converter and achieves communication-free PWM interleaving among the series-stacked converters. The proposed controller is simple in structure and is shown to converge asymptotically to the interleaved state irrespective of clock drifts among the digital signal processors. Experimental results are provided for a system of five series-connected converters showing a 10 times reduction in the current ripple compared to normal operation.

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

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 OSTI2022

Progress on Machine Learning for the SNS High Voltage Converter Modulators

The High-Voltage Converter Modulators (HVCM) used to power the klystrons in the Spallation Neutron Source (SNS) linac were selected as one area to explore machine learning due to reliability issues in the past and the availability of large sets of archived waveforms. Progress in the past two years has resulted in generating a significant amount of simulated and measured data for training neural network models such as recurrent neural networks, convolutional neural networks, and variational autoencoders. Applications in anomaly detection, fault classification, and prognostics of capacitor degradation were pursued in collaboration with the Jefferson Laboratory, and early promising results were achieved. This paper will discuss the progress to date and present results from these efforts.

Pappas, Chris↗