# US 11,909,246 B2 · Method and system for an AC battery > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,909,246 B2 - Document ID: US11909246B2 - Status: Granted - Kind: B2 - Application number: 17/539,681 - Filed: 2021-12-01 - Published: 2022-05-05 - Granted: 2024-02-20 - Earliest claimed: 2017-04-13 - Assignees: Enphase Energy, Inc. - Applicants: Enphase Energy, Inc. - Inventors: Martin Fornage; Mauricio Cespedes Moya - Web page: https://patentgrep.com/patent/US11909246B2 ## CPC - H02J 7/963: {in response to battery voltage gradient} - G01R 31/3842: combining voltage and current measurements - H02J 7/02: for charging batteries from AC mains by converters - H02J 7/40: characterised by the exchange of charge or discharge related data - H02J 7/44: between battery management systems and power sources - H02J 7/52: for charge balancing, e.g. equalisation of charge between batteries - H02J 7/60: including safety or protection arrangements - H02J 7/82: Control of state of charge [SOC] - H02J 7/933: {the cycle being controlled or terminated in response to electric parameters} - G01R 31/392: Determining battery ageing or deterioration, e.g. state of health - H02J 7/62: against overcurrent - H02J 7/65: against overtemperature - H02J 2207/20: Charging or discharging characterised by the power electronics converter - H02M 7/66: with possibility of reversal - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - 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) ## Abstract A method and system for AC battery operation. In one embodiment, the method comprises determining, at a battery management unit (BMU) coupled to an AC battery comprising a power converter and a battery that is rechargeable, a bias control voltage that indicates a state of a charge process of the AC battery; and coupling, by a bias control module of the BMU, the bias control voltage to the power converting for communicating the state of the charge process to and from the BMU and the power converter. ## Claims ### Claim 1 A method for AC battery operation, comprising: determining, at a battery management unit (BMU) coupled to an AC battery system comprising a power converter and a battery that is rechargeable, an equivalent series resistance estimation by correlating a ripple voltage and a ripple current, which exists on a DC battery during power conversion, at twice a line frequency, the equivalent series resistance estimation indicates a state of a charge (SOC) process of the AC battery system; coupling, by a bias control module of the BMU, the equivalent series resistance estimation to the power converter for communicating, without a control area network, at least one of a state of health (SoH) of the battery or a degradation of the battery to and from the BMU and the power converter; when one of a battery voltage reaches a high or low end of battery operation or a high or low end of estimated state of charge (SOC) of the battery, reducing a current when an estimated ESR increases; determining, at each of the BMU and the power converter, a bias control voltage and SOC values; and periodically synchronizing estimated SOC values with one another. ### Claim 2 (depends on 1) The method of claim 1, wherein determining the equivalent series resistance estimation is used to estimate actual battery voltage, versus observed battery voltage. ### Claim 3 (depends on 1) The method of claim 1, wherein coupling the bias control voltage to the power converter comprises regulating, by the bias control module and when the BMU does not allow charging or discharging of the battery, battery output voltage to a predefined value. ### Claim 4 (depends on 1) The method of claim 1, wherein the bias control voltage indicates a fault condition. ### Claim 5 (depends on 1) The method of claim 1, wherein the bias control voltage indicates a ready to charge state for starting the power converter. ### Claim 6 (depends on 1) The method of claim 1, further comprising balancing, by the BMU, voltage across all cells of the battery following at least one of one or more cells of the battery reaching a minimum voltage or one or more cells of the battery reaching a maximum voltage. ### Claim 7 (depends on 1) The method of claim 1, further comprising: determining, by the BMU, when an estimated SOC is below a threshold; and disconnecting, when the estimated SOC is below the threshold, the battery from the power converter. ### Claim 8 (depends on 7) The method of claim 7, further comprising periodically attempting, by the BMU, to reconnect the power converter to the battery. ### Claim 9 (depends on 8) The method of claim 8, wherein time between attempted reconnections is determined by a semi-random increasing timer. ### Claim 10 (depends on 1) The method of claim 1, wherein the power converter is a bidirectional inverter. ### Claim 11 An AC battery system, comprising: a battery that is rechargeable; a battery management unit (BMU) coupled to the battery and configured to provide an equivalent series resistance estimation by correlating a ripple voltage and a ripple current, which exists on a DC battery during power conversion, at twice a line frequency, the equivalent series resistance estimation indicates a state of a charge (SOC) process of the AC battery system; and a power converter coupled to the battery and the BMU for communicating, without a control area network, at least one of a state of health (SoH) of the battery or a degradation of the battery to and from the BMU and the power converter; when one of a battery voltage reaches a high or low end of battery operation or a high or low end of estimated state of charge (SOC) of the battery, reducing a current when an estimated ESR increases; determining, at each of the BMU and the power converter, a bias control voltage and SOC values; and periodically synchronizing estimated SOC values with one another. ### Claim 12 (depends on 11) The AC battery system of claim 11, wherein determining the equivalent series resistance estimation is used to estimate actual battery voltage, versus observed battery voltage.