Modelling of DC-DC converters based on front-to-front connected MMC for small signal studies

Abstract

The Multi-terminal DC grid is expected to be built incrementally by interconnecting existing HVDC installations. In doing so, an enabling component is the DC-DC converter which also plays the role of a power flow controller. A number of DC-DC converter topologies, targeting different applications, have been proposed in literature. However, detailed simulation models for system level studies are not developed, yet. This paper will focus on reduced order modelling and control of the Front-to-Front MMC based DC-DC converter for system level studies. The developed model is validated against a full detail average model. A simple approach to investigate poorly damped oscillations is also proposed. The approach is then used to investigate a poorly damped mode in the leg energy state that was excited by a transient in ac power.