Averaged Dynamic Model of Three-level NPC Grid-following Inverter for Examining Neutral-point Instability

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

In this paper, the dynamics of neutral-point (NP) voltage oscillations and associated instability phenomena in a three-level (3L) neutral-point clamped inverter (NPCI), operating as a grid-following (GFL) inverter, are analytically modeled. We depart from the traditional space-vector analysis and adopt a time-domain description in synchronous (dq) reference frame for system modeling. In particular, the NP voltage on the dc- side is identified as an additional system state unlike in a traditional 2L-inverter model. We obtain an averaged dynamic model of the current-controlled 3L GFL-inverter in state-space form. While the model is nonlinear and time varying, it comprehensively captures all pertinent dynamics of the GFL-inverter while acknowledging the participation of power- and control- circuit parameters in determining the NP-stability. We present a block-schematic dq-domain equivalent circuit of the average 3L GFL-inverter model delineating the 2L inverter control model contained with it and the additional dynamics arising from switching the NP branch. We utilize this model for two purposes: (a) feedback linearization of the plant model using feed-forward compensation of nonlinear and time-varying terms, which facilitates controller design using classical control synthesis techniques, and (b) improving injected grid-current quality. A full-order switched-model simulation of a three-phase GFL-inverter system in MATLAB®Simulink validates the accuracy of the proposed average dynamic model for NP-stability studies as well as grid current quality improvement.

Original languageEnglish (US)
Title of host publication2021 IEEE 22nd Workshop on Control and Modelling of Power Electronics, COMPEL 2021
PublisherInstitute of Electrical and Electronics Engineers Inc.
ISBN (Electronic)9781665436359
DOIs
StatePublished - 2021
Event22nd IEEE Workshop on Control and Modelling of Power Electronics, COMPEL 2021 - Cartagena, Colombia
Duration: Nov 2 2021Nov 5 2021

Publication series

Name2021 IEEE 22nd Workshop on Control and Modelling of Power Electronics, COMPEL 2021

Conference

Conference22nd IEEE Workshop on Control and Modelling of Power Electronics, COMPEL 2021
Country/TerritoryColombia
CityCartagena
Period11/2/2111/5/21

Bibliographical note

Funding Information:
This material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under Solar Energy Technologies Office (SETO) Agreement Number EE0009025.

Publisher Copyright:
© 2021 IEEE.

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