Input-output DC impedance modeling and stabilization of a grid-connected current-source converter-based PV system

This paper addresses the interaction dynamics in Current source converters (CSCs) interfacing large photovoltaic (PV) systems to the utility grid. 1) On the ac side, interactions of the grid impedance with the LC ac-side filter might cause uncertain resonant frequency modes. 2) On the dc-side, under uncertain characteristics of the PV source impedance (e.g. number of PV modules connected and/or uncertainty in source circuit parameters), the Nyquist stability criterion might be violated due to equivalent source/load impedance mismatch. In this paper, the ac-side LC filter dynamics are robustly damped by an improved active compensator in the CSC side. More importantly, the dc-side interactions are effectively stabilized by proposing active reshaping techniques for the dc impedance of the CSC so that the Nyquist stability criterion is maintained. Time-domain results under Matlab/Simulink environment are provided to validate the analytical results.