Online Trajectory Planning During Low-Voltage FRT of a Modular Multilevel Converter

Balancing the modular multilevel converter arm energies in case of a sudden grid voltage sag is a challenging open-loop control problem, because it requires the solution of a differential equation. Unlike existing numerical approaches, an analytical solution was obtained. Ride-through experiments are conducted on a low-voltage MMC test bench using a grid emulator. In contrast to feedback balancing alone, a faster return of the cell voltages into the region of stationary operation is achieved.