Analysis and Active Suppression of AC- and DC-Side Instabilities in Grid-Connected Current-Source Converter-Based Photovoltaic System

Current source converters (CSCs) can be a viable option to interface large photovoltaic (PV) systems to the utility grid. However, interaction dynamics in both the ac- and dc-sides might be yielded and affect the converter stability. 1) On the ac side, interactions of the grid impedance with the LC ac-side filter might cause uncertain resonant frequency modes that should be damped without affecting the converter efficiency. 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. Moreover, the real part of the dc impedance of the CSC can be negative which contributes to instabilities of the PV system. In this paper, the ac-side LC filter dynamics are robustly damped by an improved active compensator in the control structure of the CSC. More importantly, the dc-side interactions dynamics are effectively stabilized by proposing active reshaping techniques for the dc impedance of the CSC so that the Nyquist stability criterion is maintained and positive damping is added. Time-domain model is implemented under Matlab/Simulink environment to validate the analytical results.