Resonance Detection Strategy for Multiple Grid-Connected Inverters-based System Using Cascaded Second-Order Generalized Integrator

摘要

The mutual interactions in the multi-paralleled grid-connected VSIs coupled through the grid impedance tend to result in the whole system oscillating-formed resonance. Resonance current threatens the stability of grid due to the frequency and magnitude fluctuation. The paper firstly reveals the transformation of resonance point with parallel VSIs. Then, Second Order Generalized Integrator-Frequency Locked Loop (SOGI-FLL) is analyzed to extract resonance current frequency. Secondly, the paper proposes an improved method that two models of SOGI-FLL are cascaded and normalized to eliminate the effect of magnitude and frequency. The fundamental component can be completely filtered by the former part. This method is frequency self-adaptive and faster to extract unknown frequency current. Finally, the simulation results verify the effectiveness of the theoretical analysis.