Current Control of Modular Multilevel Converters Using a Daisy-Chained Distributed Control System with Communication Path Redundancy

Conventional modular multilevel converters (MMCs) include many optical fibers for gate signals. A daisy-chained distributed control system that consists of a master controller and slave cell controllers using a field bus communication protocol allows an effective reduction of the number of the fibers. Moreover, the control system provides a communication path redundancy that tolerates faults among the cell controllers or the fibers by reconfiguring the path. However, current control performance changes under the fault, due to the change of communication delays between the controllers. This paper discusses a current control model under the fault considering the communication delays in an MMC using the daisy-chained distributed control system. We derive the generalized current control model under the fault and analyze the impacts of the fault on the current control performance. The gain design for the current control is also discussed.