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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Thermoelectric power of Sachdev-Ye-Kitaev islands: Probing Bekenstein-Hawking entropy in quantum matter experiments

The Sachdev-Ye-Kitaev (SYK) model describes electrons with random and all-to-all interactions and realizes a many-body state without quasiparticle excitations and a nonvanishing extensive entropy $S_0$ in the zero-temperature limit. Its low-energy theory coincides with the low-energy theory of near-extremal charged black holes with Bekenstein-Hawking entropy $S_0$. Several mesoscopic experimental configurations realizing SYK quantum dynamics over a significant intermediate temperature scale have been proposed. We investigate quantum thermoelectric transport in such configurations and describe low-temperature crossovers out of SYK criticality into regimes either with Fermi liquid behavior, with a Coulomb blockade, or criticality associated with Schwarzian quantum gravity fluctuations. In this work, our results show that thermopower measurements can serve as a direct probe for $S_0$.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Quantum criticality in coupled hybrid metal-semiconductor islands

We show that the combined effects of a dynamical Coulomb blockade and integer quantum Hall effect in a coupled hybrid metal-semiconductor setup provide a pathway for realizing resonant tunneling in Luttinger liquids. This hybrid setup can be brought to the quantum critical regime by varying gate voltages and contact resistances. We explore the nature of quantum criticality, Kondo effect, charge fractionalization, and transport in such a hybrid setup, and verify their robust non-Fermi-liquid behaviors. In conclusion, our work opens a promising route for quantum simulating exotic zero-temperature quantum critical phenomena associated with Luttinger-liquid physics in a nanoengineered electronic circuit with well-defined quantum Hall channels.

Coulomb blockade↗
DOE OSTI2025

Virtual Agents-Based Attack-Resilient Distributed Control for Islanded AC Microgrid

Due to its dependence on a communication network, distributed secondary control of microgrids is susceptible to denial-of-service (DoS) attacks in channel shutdown mode, which may negatively impact the network connectivity and thus deteriorate the coordination and power sharing among distributed generators (DGs). Honeypot is a common method for cyber deception by introducing fake targets. However, in the context of microgrid, the misleading information spread by honeypots will also impact the system performance. This paper proposes an attack-resilient distributed control for AC microgrids utilizing virtual agents (VAs) to counteract both DoS edge and node attacks. The VAs are designed to not impact the system’s steady state during normal operation but to share information among neighboring real agents and serve as dummy targets for DoS attacks. The control with VAs is implemented by a primal-dual gradient based distributed algorithm to efficiently obtain a practical solution for voltage/frequency regulation and power sharing. The simulation results on a 4-DG test system and a modified IEEE 34-bus system show that 1) VAs do not impact the normal functionality of the test system, and 2) deploying VAs can enhance the resilience of the microgrid control against DoS edge and node attacks.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2022

Inrush Current Mitigation for Grid-Forming Inverters in Islanded Microgrids

Virtual-inertia and droop control methods are commonly used for grid-forming inverters. While the virtual inertia is used to emulate the equation of motion/frequency, if the inverter output voltage is emulated as in synchronous generators, then the method is known as the virtual synchronous generator. An inductive pulse-load, e.g., a relatively large induction motor, connection to a microgrid fed only by grid-forming inverters may lead to blackout due to high inrush currents. This article presents virtual reactance techniques to mitigate the inrush current effects and enhance the inverter’s robustness for the safe connection of inductive and dynamic loads. This article also compares the virtual inertia and droop control methods under switching inductive-dynamic loads while the proposed techniques are implemented. Experimental tests are performed considering the linear and nonlinear virtual reactance techniques, and the findings are discussed. The mitigation significantly suppresses the inrush currents while the inverters can perform a normal operation. Furthermore, the frequency and power response of the virtual inertia control with different inertia settings to a sudden change in the load is analyzed. The virtual reactance technique is tested in a laboratory-scale hardware setup of a 208V microgrid fed by 5kVA and 10kVA inverters, and the results are presented in this article.

Gursoy, Mehmetcan↗
DOE OSTI2022

Dynamic Load Inrush Current Mitigation in Islanded Microgrids Powered by Grid-Forming Inverters

Grid-forming inverters in a microgrid may trip due to high inrush current caused by a switched connection of an inductive load, e.g., a relatively large induction motor. The control scheme presented in this article includes virtual inertia control method superimposed on the cascaded controller. This article studies the impact of cascaded control scheme used for grid-forming inverter to mitigate the inrush current effects and enhance the inverter’s robustness for the safe connection of inductive and dynamic loads. Experimental tests are performed using the virtual inertia method for generating the reference angle for synchronous frame conversion. The experimental performance and sensitivity of the controller to different controller gain settings for a switched connection of an induction motor are discussed. The cascaded operation significantly mitigates the inrush currents while the inverters can perform a normal operation. The performance of the control method is tested in a laboratory-scale hardware setup of a 208V microgrid fed by 5kVA and 10kVA inverters, and the results are presented.

Gursoy, Mehmetcan↗