Stability Analysis and Enhancement of Resistance-Emulating Control-Based Grid-Connected DC Grids Based on SISO Modeling

Resistance-emulating control (REC) is an appealing method for interface converters in grid-connected DC systems because of its independence from AC-side voltage sensors. However, due to its complex internal and control dynamics, accurate and comprehensive modeling and stability analysis of REC-based grid-connected converter (GCC) remains underexplored and the corresponding stability enhancement methods have also not been developed. This article tries to deal with these important yet challenging issues. Firstly, by considering all the internal physical dynamics and control dynamics of the system, a complete and accurate small-signal single-input single-output (SISO) model of the REC-based GCC is proposed for the first time. Next, through the SISO model, accurate controller parameter design is conducted and different factors affecting system stability are intuitively and quantitatively analyzed through the standard Nyquist criterion. Finally, to enhance system stability against large disturbances, (e.g., wide variations in load power and line impedance) and improve the system dynamic performance simultaneously, a dual-variable hybrid adaptive feedback strategy based on AC current and emulating resistance feedback is proposed. Simulation and experimental results verify the accuracy of the established model and the effectiveness of the proposed method.