Bidirectional Grid-Connected Single-Power-Conversion Converter With Low-Input Battery Voltage

This study proposes a bidirectional grid-connected single-power-conversion converter with low-input battery voltage. The proposed bidirectional converter consists of a bidirectional dc-dc converter and an unfolding bridge, and the power conversion stage only corresponds to a bidirectional dc-dc converter. The bidirectional dc-dc converter can perform bidirectional power conversion between the low input battery voltage and a rectified sine wave due to its step-up/down voltage regulation functions. The unfolding bridge unfolds the rectified sine wave into the grid voltage and provides a current path to the grid. The study also proposes a control algorithm to regulate the grid current through a single power-processing stage. The control algorithm is comprised of a feed-forward nominal voltage compensator and a repetitive control scheme. The feed-forward nominal voltage compensator presets the operating point to lighten the burden of the grid current control, and the repetitive controller provides precise control of the grid current. Thus, the proposed bidirectional grid-connected single-power-conversion converter results in high power quality and high efficiency. Experimental results based on a 250-W prototype module are conducted to evaluate the performance of the converter and to verify the analysis.