# US 12,015,333 B2 · Intelligent discharge control for modular multilevel converter > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,015,333 B2 - Document ID: US12015333B2 - Status: Granted - Kind: B2 - Application number: 17/634,959 - Filed: 2020-08-12 - Published: 2022-09-29 - Granted: 2024-06-18 - Earliest claimed: 2019-08-13 - Assignees: Vestas Wind Systems A/S - Applicants: Vestas Wind Systems A/S - Inventors: Cem Özgür Gerçek; Lars Helle; Ciprian Biris - Web page: https://patentgrep.com/patent/US12015333B2 ## CPC - H02M 1/0095: {Hybrid converter topologies, e.g. NPC mixed with flying capacitor, thyristor converter mixed with MMC or charge pump mixed with buck} - H02J 3/381: {Dispersed generators} - H02M 1/32: Means for protecting converters other than automatic disconnection - H02M 1/322: {Means for rapidly discharging a capacitor of the converter for protecting electrical components or for preventing electrical shock} - H02M 7/483: Converters with outputs that each can have more than two voltages levels - H02M 7/4835: {comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage} - H02M 7/5395: by pulse-width modulation - H02J 2101/28: Wind energy - H02M 1/325: {with means for allowing continuous operation despite a fault, i.e. fault tolerant converters} - H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P) - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY ## Abstract This disclosure proposes procedures and systems for discharging system capacitors and de-energizing power transmission systems having Modular Multilevel Converter (MMC) topologies by intelligent control of MMC cell components including configuration of bypass and insert switches using integrated DC choppers to effectively de-energize MMC cell capacitors and/or DC-link capacitors under operating conditions such as after a normal stop, for protection against over-voltages, dumping turbine energy, and under certain hardware fault conditions. ## Claims ### Claim 1 A method of controlling a wind turbine modular multilevel converter (MMC) system comprising a plurality of MMC cells connected in series, each of the plurality of MMC cells comprising at least two main switches and an integrated direct current (DC) chopper, the method comprising: detecting a system discharge event; and controlling the integrated DC choppers to de-energize one or more MMC cell capacitors in each of the plurality of MMC cells in response to the system discharge event. ### Claim 2 (depends on 1) The method of claim 1 wherein controlling the integrated DC choppers comprises: enabling a first discharge loop having a current path from a first cell voltage rail, through a dump-load resistor, to a second cell voltage rail, and disabling the current path of the first discharge loop and enabling a free-wheeling loop current through the dump-load resistor and a free-wheeling diode. ### Claim 3 (depends on 2) The method of claim 2 wherein enabling and disabling the first discharge loop comprises controlling a first DC chopper switch. ### Claim 4 (depends on 3) The method of claim 3 wherein the first DC chopper switch is controlled by pulse width modulation (PWM). ### Claim 5 (depends on 2) The method of claim 2 wherein disabling the first discharge loop enables the free-wheeling loop. ### Claim 6 (depends on 1) The method of claim 1 further comprising: controlling at least one of the main switches to de-energize the one or more MMC cell capacitors; wherein the one or more MMC cell capacitors are connected to the integrated DC chopper by a first cell voltage rail and a second cell voltage rail. ### Claim 7 (depends on 6) The method of claim 6 wherein controlling the integrated DC choppers to de-energize a plurality of MMC cell capacitors comprises: enabling a first discharge loop having a current path from the first cell voltage rail, through a dump-load resistor, to the second cell voltage rail, and disabling the first discharge loop current path and enabling a free-wheeling loop current through the dump-load resistor and a free-wheeling diode. ### Claim 8 (depends on 6) The method of claim 6 wherein each of the plurality of cells comprises a cell input and a cell output) connecting the plurality of cells; and wherein the de-energizing comprises configuring at least one of the main switches to block a DC current path short from the cell input to the cell output. ### Claim 9 (depends on 8) The method of claim 8 wherein the main switches are configured to block the DC current path short for each of all the cells in a phase arm. ### Claim 10 (depends on 8) The method of claim 8 wherein the main switches are configured to block the DC current path short for each of all the cells in each of two phase arms of a phase leg. ### Claim 11 (depends on 10) The method of claim 10 wherein the method further comprises: enabling a second discharge loop having a current path from a first DC-link voltage rail, through the plurality of MMC cells to a second DC-link voltage rail. ### Claim 12 (depends on 11) The method of claim 11 wherein the second discharge loop comprises an earthing resistor. ### Claim 13 (depends on 11) The method of claim 11 wherein the second discharge loop comprises an arm inductor. ### Claim 14 (depends on 11) The method of claim 11 wherein enabling the second discharge loop comprises engaging an earthing switch. ### Claim 15 (depends on 11) The method of claim 11, wherein the method further comprises detecting an MMC cell fault. ### Claim 16 (depends on 15) The method of claim 15 wherein the MMC cell fault comprises a faulty integrated DC chopper. ### Claim 17 (depends on 11) The method of claim 11 wherein blocking the DC current path short from the cell input to the cell output comprises disengaging at least one bypass switch. ### Claim 18 (depends on 17) The method of claim 17 wherein disengaging the at least one bypass switch comprises configuring at least one of two or more main switches. ### Claim 19 A method of de-energizing a wind turbine MMC system, the MMC system comprising a plurality of series-connected MMC cells, and a DC-link having a first DC-link voltage rail and a second DC-link voltage rail, the method comprising: enabling a first discharge path from the first DC-link voltage rail, through the plurality of series-connected MMC cells, to the second DC-link voltage rail; and grounding the second DC-link voltage rail with an earthing resistor; wherein the first discharge path includes the earthing resistor. ### Claim 20 A method of de-energizing a wind turbine MMC system, the MMC system comprising a plurality of series-connected MMC cells, and a DC-link having a first DC-link voltage rail and a second DC-link voltage rail, the method comprising: enabling a first discharge loop having a current path from the first DC-link voltage rail, through the plurality of series-connected MMC cells, to the second DC-link voltage rail; and enabling a second discharge loop that includes a current path from the first DC-link voltage rail, through a second plurality of series-connected MMC cells, to the second DC-link voltage rail; wherein the first discharge loop includes MMC cells from a different phase.