To main content

Optimal Shaping of the MMC Circulating Currents for Preventing AC-Side Power Oscillations from Propagating into HVdc Grids

Optimal Shaping of the MMC Circulating Currents for Preventing AC-Side Power Oscillations from Propagating into HVdc Grids

Category
Journal publication
Abstract
A constrained optimization problem based on the Lagrange multipliers method is formulated to derive the circulating current references of Modular Multilevel Converters (MMC) directly in abc coordinates. The resulting analytic expressions for calculating the circulating current reference signals are designed to eliminate oscillations in the dc-side power flow, independently from the ac-side operation of the MMC. As a result of the constrained optimization, the circulating currents are shaped to optimally utilize the degrees of freedom provided by the internal energy buffering capacity of the MMC, to effectively decouple the ac grid conditions from the dc bus. This property of the proposed control method makes it especially suitable for preventing oscillations due to unbalanced ac grid voltage conditions from propagating into multi-terminal HVDC systems. It is shown that the power flow at the dc-side of the MMC will be most effectively decoupled from ac-side transients if the desired steady-state power flow is imposed by acting directly on the circulating current references instead of by acting on the acside current references. The operation of an MMC controlled by the proposed approach is demonstrated by simulation studies, verifying the ability of keeping the dc power flow free of second harmonic oscillations, independently
Client
  • Norges forskningsråd / 268053
Language
English
Author(s)
  • Bergna-Diaz Gilbert
  • Suul Jon Are Wold
  • Berne Erik
  • Vannier Jean-Claude
  • Molinas Cabrera Maria Marta
Affiliation
  • France
  • SINTEF Energy Research / Energisystemer
  • University of Paris-Saclay
  • Sorbonne University
  • University Paris Sud (Paris XI) Orsay
  • National Center for Scientific Research
  • Norwegian University of Science and Technology
Year
2019
Published in
IEEE Journal of Emerging and Selected Topics in Power Electronics
ISSN
2168-6777
Publisher
IEEE
Volume
7
Issue
2
Page(s)
1015 - 1030