# US 10,503,126 B2 · Access control method for parallel direct current power supplies and device thereof > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,503,126 B2 - Document ID: US10503126B2 - Status: Granted - Kind: B2 - Application number: 15/618,503 - Filed: 2017-06-09 - Published: 2017-12-21 - Granted: 2019-12-10 - Earliest claimed: 2016-06-21 - Assignees: Sungrow Power Supply Co., Ltd. - Applicants: Sungrow Power Supply Co., Ltd. - Inventors: Hua Ni; Shangfang Dai; Yanfei Yu; Zongjun Yang - Web page: https://patentgrep.com/patent/US10503126B2 ## CPC - G01R 31/40: Testing power supplies (testing photovoltaic devices H02S50/10) - G01R 31/08: Locating faults in cables, transmission lines, or networks - G01R 31/52: Testing for short-circuits, leakage current or ground faults - G05B 9/02: electric - H02H 3/16: responsive to fault current to earth, frame or mass (with balanced or differential arrangement H02H3/26 {; monitoring earth connection H02H5/105}) - H02H 7/20: for electronic equipment (for converters H02H7/10; for electric measuring instruments G01R1/36; for DC voltage or current semiconductor regulators G05F1/569; for amplifiers H03F1/52; for electronic switching circuits H03K17/08) - H02J 1/10: Parallel operation of DC sources - H02J 3/381: {Dispersed generators} - H02J 3/46: Controlling the sharing of generated power between the generators, sources or networks - H02S 50/00: Monitoring or testing of PV systems, e.g. load balancing or fault identification - H02H 3/042: {combined with means for locating the fault (locating faults in cables G01R31/08)} - H02J 2101/24: Photovoltaics - Y02E 10/56: Power conversion systems, e.g. maximum power point trackers - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - G05B: CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS (systems for controlling or regulating non-electric variables G05D; systems for regulating electric or magnetic variables G05F; control devices or systems insofar as characterised by mechanical features only G05G) - H02H: EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS (indicating or signalling undesired working conditions G01R, e.g. G01R31/00, G08B; locating faults along lines G01R31/08; emergency protective devices H01H) - H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY - H02S: GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES (obtaining electrical energy from radioactive sources G21H1/12; light sensitive inorganic semiconductor devices H10F; light sensitive organic semiconductor devices H10K30/00; thermoelectric devices H10N10/00; pyroelectric devices H10N15/00) - Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION ## Abstract The application provides an access control method of parallel direct current power supplies and a device thereof. Direct current power supplies with single insulation resistances to ground failing to meet a first preset condition or causing a total insulation resistances to fail to meet a second preset condition are disconnected from a grid-connected inverter, and direct current power supplies with single insulation resistance to ground meeting the first preset condition and enabling the total insulation resistance to meet the second preset condition are connected with the grid-connected inverter for grid-connected inverting. Unlike in conventional technology, not all the direct current power supplies connected to a direct current bus are made stop outputting, thereby avoiding the loss of inverter power generation. ## Claims ### Claim 1 An access control method for parallel direct current power supplies, performed by an access control device for parallel direct current power supplies which is applied to a grid-connected inverter, wherein, a direct current side of the grid-connected inverter is connected with n direct current power supplies in parallel via 2n switches; and the access control device for the parallel direct current power supplies comprises: a control unit and an insulation resistance detection circuit, and n is a positive integer greater than 1; wherein, one ends of n of the 2n switches are connected with positive output terminals of the n direct current power supplies in a one-to-one correspondence, and the other ends are connected with a positive input terminal of the insulation resistance detection circuit and a positive input terminal of the grid-connected inverter; one ends of the other n of the 2n switches are connected with negative output terminals of the n direct current power supplies in a one-to-one correspondence, and the other ends are connected with a negative input terminal of the insulation resistance detection circuit and a negative input terminal of the grid-connected inverter; wherein the method comprises: S101, detecting, by the insulation resistance detection circuit, values of single insulation resistances to ground of the n direct current power supplies; S102, determining, by the control unit, whether values of the single insulation resistances to ground each are greater than a first threshold; S103, controlling, by the control unit, each switch connected with a direct current power supply, a value of a single insulation resistance to ground of which is not greater than the first threshold, to be open, and controlling each switch connected with a direct current power supply, a value of a single insulation resistance to ground of which is greater than the first threshold, to be closed, in response to determining that the values of the single insulation resistances to ground are not all greater than the first threshold; S104, detecting, by the insulation resistance detection circuit, a value of a total insulation resistance to ground of direct current power supplies currently in parallel, after step S103 is performed or in a case that in step S102 all the values of the single insulation resistances to ground is greater than the first threshold; S105, determining, by the control unit, whether the value of the total insulation resistance to ground is greater than a second threshold different than the first threshold; S106, controlling, by the control unit, a switch connected with a direct current power supply, a value of a single insulation resistance to ground of which is smallest of the direct current power supplies that are currently in parallel and have the values of the single insulation resistances to ground all greater than the first threshold, to be open, in response to determining that the value of the total insulation resistance to ground is not greater than the second threshold; and repeatedly performing steps S104, S105 and S106 till the value of the total insulation resistance to ground of direct current power supplies currently in parallel is greater than the second threshold. ### Claim 2 (depends on 1) The access control method for the parallel direct current power supplies according to claim 1, wherein before step S101, the method further comprises: S201, detecting a value of an overall insulation resistance to ground of all the direct current power supplies when connected in parallel; S202, determining whether the value of the overall insulation resistance to ground is greater than the second threshold; and S203, performing a grid-connected operation on the grid-connected inverter, in a case that the value of the overall insulation resistance to ground is greater than the second threshold, wherein, step S101 is performed only in a case that the value of the overall insulation resistance to ground is not greater than the second threshold. ### Claim 3 (depends on 1) The access control method for the parallel direct current power supplies according to claim 1, wherein the first threshold and the second threshold both are: (1K/V) Ω. ### Claim 4 (depends on 2) The access control method for the parallel direct current power supplies according to claim 2, wherein the first threshold and the second threshold both are: (1K/V) Ω. ### Claim 5 (depends on 1) The access control method for the parallel direct current power supplies according to claim 1, wherein the first threshold and the second threshold both are: (VMAX PV/30 mA) Ω, and VMAX PV is the highest output voltage in direct current power supplies. ### Claim 6 (depends on 2) The access control method for the parallel direct current power supplies according to claim 2, wherein the first threshold and the second threshold both are: (VMAX PV/30 mA) Ω, and VMAX PV is the highest output voltage in direct current power supplies. ### Claim 7 An access control device for parallel direct current power supplies, applied to a grid-connected inverter, wherein, a direct current side of the grid-connected inverter is connected with n direct current power supplies in parallel via 2n switches; and the access control device for the parallel direct current power supplies comprises: a control unit and an insulation resistance detection circuit, and n is a positive integer greater than 1; wherein, one ends of n of the 2n switches are connected with positive output terminals of the n direct current power supplies in a one-to-one correspondence, and the other ends are connected with a positive input terminal of the insulation resistance detection circuit and a positive input terminal of the grid-connected inverter; one ends of the other n of the 2n switches are connected with negative output terminals of the n direct current power supplies in a one-to-one correspondence, and the other ends are connected with a negative input terminal of the insulation resistance detection circuit and a negative input terminal of the grid-connected inverter; the insulation resistance detection circuit is configured to detect values of single insulation resistances to ground of the n direct current power supplies and a value of a total insulation resistance to ground of direct current power supplies currently in parallel; and the control unit is configured to: determine whether the values of the single insulation resistance to ground of the n direct current power supplies each are greater than a first threshold; in response to determining that the values of the single insulation resistances to ground of the n direct current power supplies are not greater than the first threshold, control each switch connected with a direct current power supply, a value of a single insulation resistance to ground of which is not greater than the first threshold, to be open and control each switch connected with a direct current power supply, a value of a single insulation resistance to ground of which is greater than the first threshold, to be closed; determine whether the value of the total insulation resistance to ground of direct current power supplies currently in parallel is greater than a second threshold different than the first threshold, in response to the controlling of each switch; control, in response to determining that the value of the total insulation resistance to ground is not greater than the second threshold, a switch connected with a direct current power supply, a value of a single insulation resistance to ground of which is smallest of the direct current power supplies that are currently in parallel and have the values of the single insulation resistances to ground all greater than the first threshold, to be open; and repeatedly determine whether a value of a total insulation resistance to ground of direct current power supplies currently in parallel is greater than the second threshold, and control, in response to determining that the value of the total insulation resistance to ground is not greater than the second threshold, a switch connected with a direct current power supply, a value of a single insulation resistance to ground of which is smallest of the direct current power supplies that are currently in parallel and have the values of the single insulation resistances to ground all greater than the first threshold, to be open, till the value of the total insulation resistance to ground of the direct current power supplies currently in parallel is greater than the second threshold. ### Claim 8 (depends on 7) The access control device for the parallel direct current power supplies according to claim 7, wherein, the insulation resistance detection circuit is further configured to detect a value of an overall insulation resistance to ground of all the direct current power supplies when connected in parallel; and the control unit is further configured to determine whether the value of the overall insulation resistance to ground is greater than the second threshold, and in response to determining that the value of the overall insulation resistance to ground is greater than the second threshold, perform a grid-connected operation on the grid-connected inverter. ### Claim 9 (depends on 7) The access control device for the parallel direct current power supplies according to claim 7, wherein the control unit is further configured to output a corresponding direct current power failure warning signal when a switch is open. ### Claim 10 (depends on 7) A grid-connected inverter, wherein, a direct current side of the grid-connected inverter is connected with n direct current power supplies in parallel via 2n switches; and the grid-connected inverter comprises the access control device for the parallel direct current power supplies according to claim 7, or the access control device for the parallel direct current power supplies according to claim 7 is provided in the grid-connected inverter. ### Claim 11 (depends on 7) A grid-connected power generation system, comprising n direct current power supplies in parallel, 2n switches, a grid-connected inverter, a direct current side of which is connected with the n direct current power supplies in parallel via the 2n switches, and the access control device for the parallel direct current power supplies according to claim 7. ### Claim 12 (depends on 11) The grid-connected power generation system according to claim 11, wherein the 2n switches and the insulation resistance detection circuit are provided in a combiner box, or the insulation resistance detection circuit and the control unit are provided in the grid-connected inverter.