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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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9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Triple Phase-Shift Optimization of SiC-based Dual-Active Bridge DC/AC Converter

This paper presents a loss-optimized Triple Phase-Shift (TPS) switching strategy for Dual-Active Bridge (DAB) based converters. The proposed strategy considers minimizing total converter loss with respect to minimizing device rms cur-rents, enabling Zero-Voltage Switching (ZVS) turn-on of devices and accurate control of device turn-off current. A model for switching currents is presented, followed by a loss model and optimization strategy. A 1.3kV/100kW prototype based on SiC MOSFETs was used in this work and experimental results up to 10kW show the proposed TPS strategy to be more efficient for operation.

Vetrivelan, Adithyan↗
DOE OSTI2022

Benchmarking Real-Time Control Platforms Using a Matlab/Simulink Coder with Applications in the Control of DC/AC Switched Power Converters

In the control of DC/AC switched power converters (SPC), one of the most important aspects to be considered is the selection of the real-time control platform. The real-time control platform must be able to meet the high performance efficiency and regulation requirements of the DC/AC SPC, as these typically operate at switching frequencies in the order of kHz to MHz. For this reason, the hardware characteristics of the ADC and PWM, and the processing capacity of the real-time control platform are of vital importance when implementing advanced digital controllers that maintain voltage and current levels within regulatory standards. In this context, we aimed to perform a comparative study of the computation times of different real-time control platforms when implementing different control strategies for DC/AC switched power converters. We also analyzed the impact of the real-time control platforms on the THD of the voltages generated by the DC/AC switched power converters. With the help of this paper, researchers and developers will have criteria to select which real-time control platform to use in real-time control for DC/AC SPC applications.

42 ENGINEERING↗
DOE OSTI2022

A PWM Strategy for Cascaded H-bridges to Reduce the Loss Caused by Parasitic Capacitances of Medium Voltage Dual Active Bridge Transformers

In this paper, to reduce the power loss caused by the parasitic capacitances of medium voltage medium frequency transformers in a two-stage dc/ac converter, including a dual active bridge (DAB)-based dc/dc stage and a cascaded H-bridge (CHB)-based dc/ac stage, a PWM strategy is proposed for the dc/ac stage. For each H-bridge, by shifting the high switching frequency to one half-bridge and having the other half-bridge switching at the fundamental frequency of the ac voltage, equivalent frequencies of transformer terminal-to-ground voltages are reduced. As a result, the frequencies of charging and discharging current to the parasitic capacitance are reduced, and therefore the loss caused by the parasitic capacitances is reduced. Compared to the conventional phase-shift PWM, the proposed PWM strategy can reduce the parasitic capacitance loss by about 75%. Experimental test results of one phase in the 13.8 kV/ 100 kW converter prototype are provided to validate the approach.

Li, Haiguo↗
DOE OSTI2023

Design and Demonstration of an 850 V dc to 13.8 kV ac 100 kW Three-phase Four-wire Power Conditioning System Converter Using 10 kV SiC MOSFETs

In this paper, an 850 V dc to 13.8 kV ac 100 kW modular multilevel three-phase four-wire dc/ac converter based on 10 kV SiC MOSFETs is designed and demonstrated. The design considerations of key components, including the dc-link, device cooling, gate driver, isolated gate driver power supply (GDPS), medium voltage (MV) ac filter inductor, MV and medium frequency transformer, and the mechanical design are discussed. Two converters are designed, and two prototypes are developed, to study the converter paralleling operation and scalability. Both converters are fully tested up to their voltage and power ratings. However, the two converters are not identical. Based on the design and test results of the first converter, the MV power stage, transformer design, GDPS, as well as the low voltage power stage in the second converter are improved for smaller size and/or higher efficiency. Compared to the version 1 converter, the version 2 converter achieves 49% volume reduction and 2 percentage point efficiency improvement, with a peak efficiency of 98.4% at the rated power.

Li, Haiguo↗
DOE OSTI2021

Efficiency Optimization of Dual Active Bridge Converter Based on dV/dt Snubber Capacitors

This paper presents a lossless regenerative dV/dt snubber circuit for PWM converters to achieve high-efficiency high power-density without significant cost and reliability penalties. The dV/dt snubber employs lossless capacitors for each MOSFET device in a converter to provide an additional path to store the switching energy during turn-off transient and decrease the actual turn-off loss of the MOSFET channel. A novel mathematical turn-off loss model is built to separate the actual turn-off loss of the MOSFET channel and the recycling switching energy stored in the total equivalent output capacitance including Coss, the dV/dt snubber, and etc. Necessary snubber optimization strategy is proposed in order to balance the turn-off loss with ZVS operation range and deadtime conduction loss, and thereby achieving an optimal efficiency performance. To prove the validity and accuracy of the novel turn-off loss model and optimization strategy, the dV/dt snubber has been incorporated into a 1.3kV/200kW DC/DC and a 1kV/70kVA DC/AC PWM converters. Experimental results are given to demonstrate the validity of the proposed dV/dt snubber capacitors and optimization strategy.

Xu, Wei↗
DOE OSTI2021

Adaptive critic design-based reinforcement learning approach in controlling virtual inertia-based grid-connected inverters

In this report, an adaptive critic design (ACD) approach is proposed to control the phase and voltage of a grid-connected virtual synchronous generator (VSG). The penetration of fast responding inertia-less power converters significantly affect the stability of the power system, especially weak systems such as micro grids. The concept of virtual inertia addresses this concern by virtually emulating the behavior of a synchronous generator. However, the conventional VSG is designed based on two conditions: (i) fixed operating point and (ii) inductive grid connections. The performance of VSGs in low-voltage semi-resistive microgrids is far from optimal. To overcome the aforementioned concerns, a heuristic dynamic programing (HDP) approach is proposed to optimally control grid-connected VSGs. The neural-network-based inherence of the HDP enables the proposed technique to adapt to any impedance angle. The HDP controller includes two subnetworks: (i) the action network that controls the system optimally and (ii) the critic network, which evaluates the effectiveness of the action network. The simulation and experimental results are provided to evaluate the effectiveness of the proposed technique. As shown, the HDP-based approach illustrates a better performance in comparison with the conventional PI-based VSG in various operating conditions.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2025

Experimental Validation of a 40kW, 480V Point-to-Point DC Interlinks for Controller-Agnostic, Interoperable Networked Microgrids

This paper presents the experimental validation of point-to-point dc-interlinks for interconnecting two solar-based, laboratory-scale AC microgrids. DC interlinks provide a solution to numerous technical and operational challenges encountered in networked microgrids, including precise power flow control, stable and fast synchronization, enhanced stability, and improved voltage and frequency regulation. By decoupling microgrids through power converters, dc-interlinks enable power exchange among microgrids that can be owned by different entities (such as communities, utilities, or universities) and managed by diverse microgrid controller vendors. This characteristic makes this dc-interlinks a promising solution for networking real-world microgrids. The presented point-to-point dc interlink utilizes two four-quadrant converters: a 40kW 3-phase ac/dc regulating the dc-link voltage to 800V, and a 3-phase dc/ac controlling power flow. These converters, connected via a 20-foot dc cable, interconnect two ac microgrids operating at 480V, each featuring energy storage, photovoltaic generation, and load emulation. Experimental validation employs commercially available off-the-shelf (COTS) converters and real-world data from solar-powered microgrids in Adjuntas, Puerto Rico. To the authors’ knowledge, this work provides the first at-scale experimental validation of dc-interlinks for networked ac microgrids using COTS inverters, demonstrating their practicality and effectiveness in addressing real-world operational challenges.

Ferrari Maglia, Max [ORNL]↗
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 Bi-directional AC/DC - DC/AC Wireless Power Transfer System for Grid Support Applications

The severity of the economic impact caused by grid outages has been the driving factor for creating innovative solutions that increases interest for the deployment of distributed energy resources to reduce the impact of grid outages. This paper presents a novel topology for providing export power applications. Proposed topology can be used for grid (primary)-side of bi-directional wireless power transfer (WPT) systems, mobile energy storage systems (ESSs), and electric vehicle (EV) batteries. The proposed concept here achieves energy transfer between sources by using a hybrid frequency bi-directional ac/dc converter without an additional front-end converter stage compared to the conventional systems. Due to inherent merit of the proposed bi-directional ac/dc converter, ac input with 60 Hz grid frequency can be directly transferred through the wireless coils and can be directly converted to the dc. Results demonstrate the performance and the functionality of the single-phase bi-directional system with the input / output of 110 V ac,rms and 200 V dc at 1 kW power. Full paper will demonstrate the converter operation at 10 kW power level with additional features and control aspects.

Asa, Erdem↗