Simplified Modelling of the F2F MMC-Based High Power DC-DC Converter Including the Effect of Circulating Current Dynamics

Abstract

The Front-to-Front Modular Multilevel Converter (MMC) is one of the topologies being considered for high-voltage, high-power, dc-dc conversion. Hence, there is a need for the development of simplified models for such a converter in order to study how it behaves in a large power system. Direct interconnection of two MMC models is one option but it leads to high number of states. Moreover, symmetry of the converter offers further simplification opportunities. The use of this fact to develop a simplified models was reported in literature. However, the resulting models are only applicable when compensated modulation is used. Furthermore, these models neglect the effect of Circulating Current Suppression Controllers (CCSCs), which makes the models inaccurate in the presence of such controllers. This paper proposes a more general simplification approach that captures the effect of CCSC while minimizing the number of states. The proposed model is validated by using time domain simulations and modal (eigenvalue) analyses.