Patent ID: 11901809
Assignee: VESTAS WIND SYSTEMS A/S
Field: Electrical machinery, apparatus, energy (Electrical engineering)
Classification: CPC H  Y | IPC H

Claim 5:
6. A controller for a Modular Multilevel Converter (MMC) including a plurality of cells connected in series between a positive rail and a negative rail and wherein each cell of the plurality of cells includes a bypass switch, an insert switch, and a cell capacitor, wherein the plurality of cells is connected in parallel to a Direct Current (DC) link capacitor, the controller configured to perform an operation comprising:
driving a bypass current from an auxiliary power source through the bypass switch of each of the plurality of cells;
in response to a summed voltage across the cell capacitors in the plurality of cells satisfying a drive threshold, driving an insert current from the cell capacitors through the insert switch of each of the plurality of cells; and
in response to a voltage across the DC link capacitor satisfying a pre- charge threshold, opening a circuit breaker connecting the auxiliary power source to a rectifier and connecting a wind turbine generator, via the positive rail and negative rail, to an external power line,
wherein driving the bypass current includes tuning a rate at which individual bypass switches switch to equalize charges in the plurality of cell capacitors as the cell capacitors charge; and wherein driving the insert current includes tuning a rate at which individual insert switches switch to equalize charges in the plurality of cell capacitors as the cell capacitors discharge, and
wherein the operation further comprises while driving at least one of the bypass current and the insert current, measuring a difference in voltage level of each of the cell capacitors; and in response to the difference exceeding a difference threshold, stopping the auxiliary power source from charging the cell capacitors and the cell capacitors from charging the DC link capacitor.