Abstract
Voltage source inverters (VSIs) with vector control based on phase-locked loop (PLL) suffer instability when connecting to a very weak AC grid (short circuit ratio (SCR) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ < $</tex-math></inline-formula> 1.3). The conventional inductive grid impedance compensation for the PLL by virtually reducing the grid impedance can stabilize this connection. However, the analysis in this paper indicates that its stabilization effectiveness is sensitive to grid impedance variance and, indeed, overcompensation causes the PLL instability. Therefore, in this paper, an improved grid impedance compensation for the PLL is proposed to achieve the same stabilization for very-weak-grid connection and possess a good tolerance of grid impedance variance and overcompensation. A comprehensive small-signal model of the VSI using the proposed PLL’s grid impedance compensation is derived for stability analysis and parameter design. The time-domain simulation for this VSI is built to validate the stability analysis. Comparison studies for both proposed and conventional PLL’s grid impedance compensation are conducted including the stability effectiveness, VSI performance and grid impedance variance.
Highlights
V OLTAGE source inverters (VSIs) with phase-locked loop (PLL)-based vector control are widely used for renewable energy integration
To stabilize the rated power injection when connecting to a very weak grid (SCR
PLL-based vector control can be improved via adding additional compensation to allow the very weak grid connection (SCR
Summary
V OLTAGE source inverters (VSIs) with PLL-based vector control are widely used for renewable energy integration. To stabilize the rated power injection when connecting to a very weak grid (SCR
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