Modular multilevel converter capacitor voltage ripple reduction

Aspects of capacitor voltage ripple reduction in modular multilevel converters are described herein. In one embodiment, a power converter system includes a modular multilevel converter (MMC) electrically coupled and configured to convert power between two different power systems. The MMC includes one or more phase legs having a cascade arrangement of switching submodules, where the switching submodules include an arrangement of switching power transistors and capacitors. The MMC further includes a control loop including a differential mode control loop and a common mode control loop. The differential control loop is configured to generate a differential control signal based on a target modulation index to reduce fundamental components of voltage ripple on the capacitors, and the common mode control loop is configured to inject 2nd order harmonic current into a common mode control signal to reduce 2nd order harmonic components of the voltage ripple on the capacitors.