Frequency converter-driven oscillations in weak grids: explanation and damping improvement

Guanglu Wu, Huadong Sun, Bing Zhao, Shiyun Xu, Xi Zhang, Agustí Egea Àlvarez, Shanshan Wang, Gen Li, Yingbiao Li, Xiaoxin Zhou

Research output: Contribution to journalArticlepeer-review

Abstract

Low-frequency oscillations have been reported in several weak-grids-connected voltage-source-converter(VSC) systems. Although efforts have been devoted to understand the parametric and sensitivity impact of the VSC controller gains, a general formulation of the oscillation mechanism is still missing. Using transfer function dynamic modelling approach, we find that the outer loop active power control’s bandwidth mainly determines the oscillation frequency. The PLL introduces a large phase lag around the frequency of the PLL bandwidth in weak grids which decreases the oscillation damping. A simple but effective PI+Clegg integrator (CI) compensator is proposed to replace the standard outer loop active power controller compensating the PLL’s phase delay and increase the oscillation damping. The results are verified in a real time digital simulator.
Original languageEnglish
Number of pages4
JournalIEEE Transactions on Power Systems
Publication statusAccepted/In press - 30 Jun 2021

Keywords

  • weak grids
  • low frequency oscillations
  • oscillation damping

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