Analysis of Interoperability between DC-Voltage-Droop-Controlled MMCs with Grid-Forming Functionality in a MTDC Grid

In this article, the interoperability between droop-controlled Modular Multilevel Converters (MMC) with Grid-Forming (GFM) functionality in a 3-terminal DC grid is investigated. Two possible implementations of GFM control, namely Virtual Synchronous Machine (VSM-GFM) and matching-GFM, are combined with two implementations of DC voltage droop. A small-signal analysis on a three-terminal asymmetrical monopolar DC grid is conducted to identify the limitations of the control parameters related to system stability and dynamic performance. Time-domain simulations are conducted to analyze the effect of control parameters on system response. The results demonstrate the interoperability between the two control options, subject to some control parameter limitations.