Combined voltage balancing techniques of the DC link in five-level medium voltage NPC back-to-back converters for offshore renewable generation

The voltage balancing of the dc-link capacitors in an electric drive system with five-level neutral-point-clamped converters is investigated in this paper. A properly modified space-vector-modulation technique is utilized in combination with a multilevel dc/dc converter for controlling the capacitor voltages. An advanced algorithm has been developed for reducing the losses of the electric drive system and for ensuring that the capacitor voltages are balanced in every operating condition. The developed electric drive system can be used in offshore power plants for driving medium voltage generators. Selective simulation results are presented to validate the theoretical considerations.