Comparative Analysis on DC-Link Voltage Synchronization Controllers for Dual-Port Grid-Forming Voltage-Source Converters

Recently, the concept of dual-port grid-forming (DGFM) voltage-source converter (VSC) has been introduced. The DGFM VSCs utilize a DC-link voltage synchronization control (DVSC) to impose both a stable DC-link voltage and an AC voltage that can synchronize with an AC grid. There are two major types of DVSC. The first type consists of a proportional-integral (PI) DC-link voltage control (DVC) in parallel with an active power feedforward control (PFF). The other type utilizes a lead-compensator (LC) DVC to generate an operating frequency for the VSC without the PFF. This paper conducts a comparative analysis for these two types of DVSC. First, a small-signal model is established for the DGFM VSC using the PI+PFF DVSC and the LC DVSC, respectively. Based on the small-signal models, it is revealed that the PFF can separate the DVC and the synchronization control of the PI+PFF DVSC into two distinct control loops, whereas the DVC and the synchronization control of the LC-based DVSC are integrated into a single control loop. However, the DVC loops of these two DVSCs exhibit similar control structures, and their open-loop transfer functions are convertible. This indicates that the DC-link voltage dynamics of the DGFM VSC using the two DVSCs are similar, but their synchronization dynamics exhibit noticeable differences. The steady-state characteristics of these two DVSCs are also analyzed and compared. Simulation results validate the established small-signal models and the comparative analysis.