Sub-Module Voltage Control in DAB Assisted Modular Multilevel Converter for Low Voltage Applications

Modular Multilevel Converters efficiency, modularity and power quality make them perfectly suitable for high and medium voltage applications. The main drawbacks are the high capacitances required, numerous measurements system and high control complexity. These problems make the converter unsuitable for low voltage applications, mainly because of the limited space and the complexity involved. In order to solve these issues modification to the classical MMC topology has been proposed. This work presents a method to control the floating capacitor voltages when a low value of capacitance is considered, and Dual Active Bridge converters are used to interlink the MMC Sub-Modules. The proposed control only measures one capacitor of a stack, and significantly reduces the control complexity while maintaining a low voltage ripple. The control is validated through simulations and a single-phase low scale prototype.