Grid-forming VSC control in four-wire systems with unbalanced nonlinear loads

Ruben Lliuyacca, Juan M. Mauricioa, Antonio Gomez-Exposito, Mehdi Savaghebi, Josep M. Guerrero

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40 Citations (Scopus)
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Abstract

A grid-forming voltage source converter (VSC) is responsible to hold voltage and frequency in autonomous operation of isolated systems. In the presence of unbalanced loads, a fourth leg is added to provide current path for neutral currents. In this paper, a novel control scheme for a four-leg VSC feeding unbalanced linear and nonlinear loads is proposed. The control is based on two control blocks. A main control commands the switching sequence to the three-phase VSC ensuring balanced three-phase voltage at the output; and an independent control to the fourth leg drives neutral currents that might appear. The proposed control is noninvasive in the sense that both control blocks are independently implemented, avoiding the use of complex modulation techniques such as 3D-SVPWM. Moreover, the main control is deployed in dqo reference frame, which guarantees zero steady-state error, fast transient response during system disturbances and mitigation of harmonics when nonlinear loads are present. Simulations and experimental results are presented to verify the performance of the proposed control strategy.
Original languageEnglish
JournalElectric Power Systems Research
Volume152
Pages (from-to)249-256
Number of pages8
ISSN0378-7796
DOIs
Publication statusPublished - Nov 2017

Keywords

  • VSC
  • Four-leg
  • Unbalanced loads
  • Nonlinear
  • Neutral phase
  • Isolated

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