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Title: Steady-State Modeling of Modular Multilevel Converter Under Unbalanced Grid Conditions

This paper presents a steady-state model of MMC for the second-order phase voltage ripple prediction under unbalanced conditions, taking the impact of negative-sequence current control into account. From the steady-state model, a circular relationship is found among current and voltage quantities, which can be used to evaluate the magnitudes and initial phase angles of different circulating current components. Moreover, in order to calculate the circulating current in a point-to-point MMC-based HVdc system under unbalanced grid conditions, the derivation of equivalent dc impedance of an MMC is discussed as well. According to the dc impedance model, an MMC inverter can be represented as a series connected R-L-C branch, with its equivalent resistance and capacitance directly related to the circulating current control parameters. Experimental results from a scaled-down three-phase MMC system under an emulated single-line-to-ground fault are provided to support the theoretical analysis and derived model. In conclusion, this new models provides an insight into the impact of different control schemes on the fault characteristics and improves the understanding of the operation of MMC under unbalanced conditions.
Authors:
 [1] ; ORCiD logo [1] ;  [1] ;  [1] ; ORCiD logo [1] ;  [1]
  1. Univ. of Tennessee, Knoxville, TN (United States)
Publication Date:
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
IEEE Transactions on Power Electronics
Additional Journal Information:
Journal Volume: 32; Journal Issue: 9; Journal ID: ISSN 0885-8993
Publisher:
IEEE
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE; National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
30 DIRECT ENERGY CONVERSION; DC equivalent impedance; high-voltage direct-current (HVdc); modular multilevel converter (MMC); single-line-to-ground (SLG) fault; steady-state analysis; unbalanced conditions
OSTI Identifier:
1394585