Novel individual voltage balancing control scheme for multilevel cascade active-front-end rectifier

In this study, a novel individual voltage balancing control scheme for multilevel cascade active-front-end rectifier is proposed to allow a different voltage setting capability among different dc outputs in series. First, the proportional resonant controller and admittance compensation controller are introduced for the active inner-current control loop of cascade active-front-end rectifier to achieve better steady-state and dynamic performance. Second, an assumption based on conservation of energy is proposed to decouple a series connected ac-dc system into several individual subsystems to facilitate the individual dc-bus controller design. Both simulation and experimental results based on the cascade two-unit cascade dual-buck/boost-type active-front-end rectifier proved the effectiveness of the proposed individual balancing control scheme, which also verified the proposed assumption.