Capacitor voltage balance of MMC converters in bidirectional power flow operation

Abstract

Modular multilevel cascaded converter offers several advantages for high voltage DC transmission systems such as high modularity and power quality. However, they also present an interesting challenge from the control point of view, due to its coupled current dynamics and the voltage balance of floating capacitors. This work presents a voltage balance scheme which does not affect the input nor the output voltages and currents, and its dynamics is independent on the power operating point. Simulations results show a good dynamic of the voltage balance under changes in the DC voltage reference and reversion on the power flow.