Synchronous Machine Imitation Control of MMC Stations Adaptable for Both Strong and Weak Grids

A fast increasing proportion of renewable energy is the main development trend in today's power systems. The modular multilevel converter (MMC) station adaptable for both strong and weak grids is a potential solution when connecting to AC grids with a high proportion of power electronics. In this paper, a synchronous machine imitation control scheme of the MMC stations is proposed. The proposed control scheme consists of the basic control for normal operation and the additional control for AC fault riding through. With the basic control, the MMC station behaves as a synchronous machine. Then, based on small disturbance stability analysis, the low frequency damping characteristics are analyzed, demonstrating the proposed control's adaptability to both strong and weak grids under small disturbance. For the additional control, its performance under large disturbance is studied by time domain simulation. The time domain simulations are carried out in PSCAD/EMTDC for both the weak and strong grids, and the feasibility of the additional control under AC fault is also verified.