An unified d-q transformation based balancing controller for cascaded multilevel converter

The contribution of this paper is to investigate new feedback based balancing control frameworks for cascaded multilevel converters which could realize fast balancing( comparable to modulation based approach) and easy extension to high level system simultaneously. The presented method could achieve:(1)decoupled active and reactive current.(2) decoupled nominal controller and balancing controller.(3)definable, fast balancing process.(4)easy extension to higher level system and systematic, flexible parameter tuning process. This unified balancing control framework is derived through two consecutive coordinate transformations(based on nature of balancing process) in conjunction with an optimization idea proposed in [1][2]. In order to illustrate this idea, comparison studies are performed to compare this strategy with several previously known controller designs through both theoretical analysis and simulation validations.