Robust DC Grid Voltage Support in a Single-Stage PV Converter

This paper presents a controller for a direct current (DC) grid-connected single-stage solar photovoltaic (PV) converter. The proposed controller provides both static and dynamic voltage support to the grid voltage. Unlike the common practice, it allows a small and controlled offset in the PV voltage in proportion to the power flowing through the converter, which enhances the system’s stability margins. A novel feedback branch from the grid voltage is introduced to enable grid voltage support. Additionally, the controller includes a current-limiting feature to protect the converter switches from overcurrent transients. The proposed approach combines and designs the voltage and current controllers using an optimal full-state feedback approach. This results in a systematic design with optimal and robust properties. Detailed simulations, comparisons, and experimental results are presented in this paper to verify the effectiveness of the proposed approach. Particularly, the experimental findings demonstrate improved stability during local load disturbances and grid fluctuations, with lower voltage drops, reduced grid current variations, lower stress on the grid, and reduced losses in the grid network compared to conventional controllers.