A Current Controller Gain Characterization of Weak Grid Coupled Solar Inverter Through Impedance Interaction Modeling

The interface inverters arbitrate the network impedance based on the source characteristics for efficient solar energy harvesting. The wide impedance arbitration capability of the interface inverter defines the wide operational integrity with the ac network. In the weak grid scenario, the uncompensated grid inductance beyond point of common coupling (PCC) offers the negative damping for power oscillations at the PCC tugs the system toward instability. In this article, the negative damping influence due to interactions between the system impedance (filter inductance and grid power injection resistance) and ac network impedance (grid inductance) on the inverter closed-loop controller is characterized by observing the natural phase deviations in real and imaginary axis. Through distinguished system's natural response, a novel second-order system impedance model is derived, and proposed current controller gain characterization aiming to achieve positive damping to mitigate the PCC's oscillations. Further tuning of the controller based on the natural response of the derived impedance model accomplishes the enhanced grid injected power quality. The efficacy of the derived system impedance model along with coherence of current controller gain is demonstrated on hardware for enhanced power quality under the stable operating region.