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

Claim 10:
11. A Modular Multilevel Converter (MMC), comprising: a positive rail; a negative rail; a Direct Current (DC) link, including a DC link capacitor, connected between the positive rail and the negative rail; a rectifier, connected between the positive rail and the negative rail, and selectively connected to an auxiliary power source in a wind turbine generator (WTG), wherein the rectifier supplies DC power from auxiliary power source of the WTG on the positive rail and the negative rail having a rectified peak voltage below a pre-charge threshold for the DC link capacitor; a plurality of cells, connected in series between the positive rail and the negative rail, each cell of the plurality of cells comprising: a cell capacitor, connected between a first node and a second node; an insert switch, connected to the first node and a third node; a bypass switch, connected to the third node and the second node; a first flow diode, configured to allow current flow from the third node to the first node and prevent current flow from the first node to the third node; a second flow diode, configured to allow current flow from the second node to the third node and prevent current flow from the third node to the second node; and a gate controller, configured to:
control a voltage across the DC link capacitor and the cell capacitor by switching open and closed the insert switch and the bypass switch of respective ones of the plurality of cells to charge the cell capacitors in the plurality of cells beyond a nominal voltage and then switching open and closed the insert switch and the bypass switch to discharge the cell capacitors to charge the DC link capacitors to the pre- charge threshold, and to drive a bypass switch current includes tuning a rate at which individual bypass switches switch to equalize charges in the cell capacitors as the cell capacitors charge; and to drive an insert switch current includes tuning a rate at which individual insert switches switch to equalize charges in the of cell capacitors as the cell capacitors discharge.