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Title: Synthesizing Virtual Oscillators to Control Islanded Inverters

Abstract

Virtual oscillator control (VOC) is a decentralized control strategy for islanded microgrids where inverters are regulated to emulate the dynamics of weakly nonlinear oscillators. Compared to droop control, which is only well defined in sinusoidal steady state, VOC is a time-domain controller that enables interconnected inverters to stabilize arbitrary initial conditions to a synchronized sinusoidal limit cycle. However, the nonlinear oscillators that are elemental to VOC cannot be designed with conventional linear-control design methods. We address this challenge by applying averaging- and perturbation-based nonlinear analysis methods to extract the sinusoidal steady-state and harmonic behavior of such oscillators. The averaged models reveal conclusive links between real- and reactive-power outputs and the terminal-voltage dynamics. Similarly, the perturbation methods aid in quantifying higher order harmonics. The resultant models are then leveraged to formulate a design procedure for VOC such that the inverter satisfies standard ac performance specifications related to voltage regulation, frequency regulation, dynamic response, and harmonic content. Experimental results for a single-phase 750 VA, 120 V laboratory prototype demonstrate the validity of the design approach. They also demonstrate that droop laws are, in fact, embedded within the equilibria of the nonlinear-oscillator dynamics. This establishes the backward compatibility of VOC in that, whilemore » acting on time-domain waveforms, it subsumes droop control in sinusoidal steady state.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
NREL Laboratory Directed Research and Development (LDRD)
OSTI Identifier:
1248326
Report Number(s):
NREL/JA-5D00-64761
Journal ID: ISSN 0885-8993
DOE Contract Number:
AC36-08GO28308
Resource Type:
Journal Article
Resource Relation:
Journal Name: IEEE Transactions on Power Electronics; Journal Volume: 31; Journal Issue: 8; Related Information: IEEE Transactions on Power Electronics
Country of Publication:
United States
Language:
English
Subject:
24 POWER TRANSMISSION AND DISTRIBUTION; averaging; droop control; microgrids; nonlinear oscillator circuits; synchronization; Van der Pol oscillators

Citation Formats

Johnson, Brian B., Sinha, Mohit, Ainsworth, Nathan G., Dorfler, Florian, and Dhople, Sairaj V. Synthesizing Virtual Oscillators to Control Islanded Inverters. United States: N. p., 2016. Web. doi:10.1109/TPEL.2015.2497217.
Johnson, Brian B., Sinha, Mohit, Ainsworth, Nathan G., Dorfler, Florian, & Dhople, Sairaj V. Synthesizing Virtual Oscillators to Control Islanded Inverters. United States. doi:10.1109/TPEL.2015.2497217.
Johnson, Brian B., Sinha, Mohit, Ainsworth, Nathan G., Dorfler, Florian, and Dhople, Sairaj V. Mon . "Synthesizing Virtual Oscillators to Control Islanded Inverters". United States. doi:10.1109/TPEL.2015.2497217.
@article{osti_1248326,
title = {Synthesizing Virtual Oscillators to Control Islanded Inverters},
author = {Johnson, Brian B. and Sinha, Mohit and Ainsworth, Nathan G. and Dorfler, Florian and Dhople, Sairaj V.},
abstractNote = {Virtual oscillator control (VOC) is a decentralized control strategy for islanded microgrids where inverters are regulated to emulate the dynamics of weakly nonlinear oscillators. Compared to droop control, which is only well defined in sinusoidal steady state, VOC is a time-domain controller that enables interconnected inverters to stabilize arbitrary initial conditions to a synchronized sinusoidal limit cycle. However, the nonlinear oscillators that are elemental to VOC cannot be designed with conventional linear-control design methods. We address this challenge by applying averaging- and perturbation-based nonlinear analysis methods to extract the sinusoidal steady-state and harmonic behavior of such oscillators. The averaged models reveal conclusive links between real- and reactive-power outputs and the terminal-voltage dynamics. Similarly, the perturbation methods aid in quantifying higher order harmonics. The resultant models are then leveraged to formulate a design procedure for VOC such that the inverter satisfies standard ac performance specifications related to voltage regulation, frequency regulation, dynamic response, and harmonic content. Experimental results for a single-phase 750 VA, 120 V laboratory prototype demonstrate the validity of the design approach. They also demonstrate that droop laws are, in fact, embedded within the equilibria of the nonlinear-oscillator dynamics. This establishes the backward compatibility of VOC in that, while acting on time-domain waveforms, it subsumes droop control in sinusoidal steady state.},
doi = {10.1109/TPEL.2015.2497217},
journal = {IEEE Transactions on Power Electronics},
number = 8,
volume = 31,
place = {United States},
year = {Mon Aug 01 00:00:00 EDT 2016},
month = {Mon Aug 01 00:00:00 EDT 2016}
}
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