A Simplified Analysis of Equivalent Resistance in Modular Multilevel Converters with Parallel Functionality

The advantages of modular multilevel converters (MMC) over conventional two-level converters have lead to new emerging topologies and applications. The MMC with series/parallel connectivity (MMSPC) is one of the more recent topologies that can provide stable and efficient sensorless operation by introducing an additional parallel connection state between modules. However, while the parallel functionality has great potential in simplifying control and monitoring, it complicates the analysis of the system. The equivalent resistance of the MMC can be helpful in analyzing the conduction losses and also in designing appropriate heat management systems. Estimating the equivalent resistance of an MMC structure with half-bridge submodules is a straightforward procedure. However, performing a similar analysis for MMSPCs is more difficult, mainly because of the parallel state. In this paper, a simplified semi-analytical equivalent-resistance analysis method for MMSPC with full-bridge submodules (SM) is presented that can increase the speed of analyzing the system. Furthermore, the derived equations are compared to MMC with half-bridge SMs to provide better insight into the effect of varying parameters of the system.