Design Aspects for Achieving High Bandwidth Series and Parallel Multicell Converters

Series and parallel multicell converters (SMCs and PMCs) have been conventionally used in high-voltage and high-power applications. Recently, due to the improved efficiency with the increase of the number of cells, they are also applied in small power converters with high power density. The higher the number of cells, the higher the apparent switching frequency, so the filter requirements are reduced, which means less energy is stored in the passive components. This potentially allows for faster dynamic responses in closed-loop operation, i.e., higher bandwidth of the converters. This article highlights the filter design and the importance of using an appropriate modulator for SMCs in order to reach high bandwidths, mainly when the number of cells increases. It is underlined, through a comparison with PMC, that SMC topologies are more sensitive to the modulation strategy. SMC and PMC performances of 2-kW converters are evaluated and compared through simulations implemented in software PLECS and validated using an experimental test bench.