Passivity Principle-Based Active Damper Design to Enhance Stability of a Voltage Source Converter for Weak Grid Scenario

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Abstract
The dynamic interaction between an LCL filter-based voltage source converter and a weak grid leads to instability. A capacitor-current feedback active-damping technique, with additional sensors, is commonly employed to address high-frequency instability problems. High bandwidth PLL, can expand non-passive regions in low-frequency zones. Grid-current feedback-based active damping is proposed and employed in an Open Loop Synchronization (OLS) based current control for grid-connected converters to overcome instability and oscillation problems. The high-frequency non-passive region is made passive via the active damper with a wider phase margin to enhance stability in weak grids. This paper provides a passivity-based damper design along with the analysis and design of the OLS control. The system’s rigidity against variations in the grid impedance is demonstrated using an admittance-based stability analysis. The proposed control provides stable operation even at a very low short circuit ratio (SCR≤ 2). The proposed procedure can be exercised in both single-phase and three-phase systems. Simulation studies and laboratory experiments are conducted to verify the proposal and controller design.

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