Assessment and performance evaluation of DC-side interactions of voltage-source inverters interfacing renewable energy systems

This paper presents a performance characterization and efficient modeling of the dc-side interactions between renewable dc resources and interfacing voltage-source inverters (VSIs). The VSI is considered in both grid-connected and islanded modes of operation. On the other side, the dc source is modeled by an equivalent and a detailed circuit. In the former, an ideal current-source in parallel to a dc capacitor is used to represent a non-dispatchable source whereas an ideal dc voltage source is used to represent a dispatchable dc source. In the latter, an additional dc/dc boost converter interfaces the dc source to regulate the input dc-link voltage of the VSI. In all topologies, computationally-efficient small-signal admittance-based models, i.e. transfer-functions, are thoroughly developed for the dc source as well as the VSI. Using the Nyquist stability criterion, it is shown that the dc-link voltage dynamics is negatively affected under some operating conditions. The worst performance is yielded when the dc source is modeled by an ideal voltage source where the dc-link voltage is not controlled by the VSI. On the contrary, the dc/dc boost converter enhances the system damping. The dc-link voltage-controlling VSIs show the most damped performance. In order to enhance the system damping, active stabilizing compensators are proposed and embedded in the conventional control structure of VSIs. Large-signal time-domain simulation model is implemented under Matlab/Simulink environment to validate the small-signal models and show the effectiveness of the proposed compensators.