Linearized Capacitor Voltage Control Methods for Modular Multilevel Converters

The submodule capacitor voltages in modular multilevel converters (MMC) must be maintained at their nominal values to ensure reliable operation. Traditional methods for capacitor voltage control (including averaging control, arm-balancing control, and individual-balancing control) exhibit limitations of nonlinear controlled plants and strong coupling between different closed loops, which complicates controller design and hampers the enhancement of dynamic performance. This paper proposed a series of linearized control methods for the submodule capacitor voltage control of MMCs. With these methods, the transfer function of each closed-loop controlled plant becomes a pure integrator, thereby simplifying the controller design process. The efficacy of the proposed control methods is validated through experimental results obtained from a downscaled MMC prototype.