# US 11,309,789 B2 · Inverter and soft-start method for the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,309,789 B2 - Document ID: US11309789B2 - Status: Granted - Kind: B2 - Application number: 17/024,715 - Filed: 2020-09-18 - Published: 2021-05-06 - Granted: 2022-04-19 - Earliest claimed: 2019-11-05 - Assignees: Delta Electronics (Shanghai) Co., Ltd. - Applicants: Delta Electronics (Shanghai) Co., Ltd. - Inventors: Qikang Wei; Feidong Xu; Xuancai Zhu - Web page: https://patentgrep.com/patent/US11309789B2 ## CPC - H02M 1/36: Means for starting or stopping converters - H02M 1/08: Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters - H02M 7/53871: {with automatic control of output voltage or current} - H02M 7/53876: {based on synthesising a desired voltage vector via the selection of appropriate fundamental voltage vectors, and corresponding dwelling times} - H02M 1/0009: {Devices or circuits for detecting current in a converter} - 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 The invention discloses an inverter and a soft-start method for the same. The inverter is electrically connected between a DC power supply and a grid and includes a main power circuit electrically coupled to the grid through a relay, a filter, the relay, and a controller electrically connected with the main power circuit and the relay, respectively. The soft-start method includes: sampling a grid voltage of the grid; calculating an output voltage of the controller, and calculating a virtual current based on the output voltage of the controller, the grid voltage and a virtual impedance; and performing current closed-loop control by taking the virtual current as a feedback signal and sending a relay control signal to turn on the relay when a steady state is reached. The invention enables the soft start of the inverter without increasing any hardware circuit, such as a starting resistor, or the like. ## Claims ### Claim 1 A soft-start method for an inverter electrically connected between a DC power supply and a grid, the inverter comprising a main power circuit, a filter, a relay, and a controller, and the main power circuit electrically coupled to the grid through the relay, and the controller electrically connected with the main power circuit and the relay, respectively, the soft-start method comprising: sampling a grid voltage of the grid; calculating an output voltage of the controller, and calculating a virtual current based on the output voltage of the controller, the grid voltage and a virtual impedance; and performing current closed-loop control by taking the virtual current as a feedback signal, and sending a relay control signal to turn on the relay upon a steady state being reached. ### Claim 2 (depends on 1) The soft-start method for the inverter according to claim 1, further comprising: sampling an inverter current, and comparing the inverter current with a threshold value; if the inverter current is greater than or equal to the threshold value, choosing the inverter current as the feedback signal for the current closed-loop control; and if the inverter current is less than the threshold value, keeping on taking the virtual current as the feedback signal for the current closed-loop control. ### Claim 3 (depends on 2) The soft-start method for the inverter according to claim 2, further comprising: comparing the virtual current with a current reference to generate a current error, and determining the output voltage of the controller corresponding to the current error through a current regulator. ### Claim 4 (depends on 3) The soft-start method for the inverter according to claim 3, further comprising: sampling a DC bulk voltage, performing voltage loop control based on the DC bulk voltage and a DC bulk reference value, and taking an output of the voltage loop as the current reference. ### Claim 5 (depends on 4) The soft-start method for the inverter according to claim 4, further comprising: performing amplitude limit control to the output of the voltage loop. ### Claim 6 (depends on 4) The soft-start method for the inverter according to claim 4, wherein the inverter is a single-phase inverter coupled to a single-phase grid through the relay, or the inverter is a three-phase inverter coupled to a three-phase grid through the relay. ### Claim 7 (depends on 6) The soft-start method for the inverter according to claim 6, when the inverter is a three-phase inverter coupled to a three-phase grid through the relay, further comprising: converting a three-phase grid voltage and a three-phase inverter current into a dq-axis voltage and a dq-axis current in a dq synchronous rotating coordinate system through coordinate transformation. ### Claim 8 (depends on 7) The soft start method for the inverter according to claim 7, further comprising: taking the output of the voltage loop as a d-axis current reference, and setting a q-axis current reference to be a preset value. ### Claim 9 (depends on 3) The soft-start method for the inverter according to claim 3, wherein the controller sends the relay control signal to turn on the relay after the current error is less than an error threshold value. ### Claim 10 (depends on 2) The soft-start method for the inverter according to claim 2, wherein the threshold value is set to be greater than a maximum normal inverter current when the relay is turned off. ### Claim 11 (depends on 1) The soft-start method for the inverter according to claim 1, wherein the virtual current is calculated by the following formula: l v = ( V e - V g ) Z v , wherein Iv is the virtual current, Ve is the output voltage of the controller, Vg is the grid voltage, and Zv is the virtual impedance. ### Claim 12 (depends on 1) The soft-start method for the inverter according to claim 1, wherein the controller sends the relay control signal to turn on the relay after a delay time. ### Claim 13 An inverter electrically connected between a DC power supply and a grid, and comprising a main power circuit, a filter, a relay, a controller, and the main power circuit electrically coupled to the grid through the relay, and the controller electrically connected with the main power circuit and the relay, respectively, the controller comprising: a sampling unit for sampling a grid voltage of the grid; a virtual current calculating unit for calculating an output voltage of the controller, and calculating a virtual current based on the output voltage of the controller, the grid voltage and a virtual impedance; and a current control unit for performing current closed-loop control by taking the virtual current as a feedback signal, and sending a relay control signal to turn on the relay upon a steady state being reached. ### Claim 14 (depends on 13) The inverter according to claim 13, wherein the sampling unit further samples an inverter current; the controller further comprises a feedback selection unit configured to compare the inverter current with a threshold value; if the inverter current is greater than or equal to the threshold, choosing the inverter current as the feedback signal for the current closed-loop control; and if the inverter current is less than the threshold value, keeping on taking the virtual current as the feedback signal for the current closed-loop control. ### Claim 15 (depends on 14) The inverter according to claim 14, wherein the current control unit further compares the virtual current with a current reference to generate a current error, and determines the output voltage of the controller corresponding to the current error through a current regulator. ### Claim 16 (depends on 15) The inverter according to claim 15, wherein the sampling unit further samples a DC bulk voltage, and the controller further comprises a voltage control unit for performing voltage loop control based on the DC bulk voltage and a DC bulk reference value and taking an output of the voltage loop as the current reference. ### Claim 17 (depends on 16) The inverter according to claim 16, wherein the voltage control unit further comprises an amplitude limit unit to perform amplitude limit control to the output of the voltage loop. ### Claim 18 (depends on 16) The inverter according to claim 16, wherein the inverter is a single-phase inverter coupled to a single-phase grid through the relay, or the inverter is a three-phase inverter coupled to a three-phase grid through the relay. ### Claim 19 (depends on 18) The inverter according to claim 18, when the inverter is a three-phase inverter coupled to a three-phase grid through the relay, the controller further comprises: a coordinate conversion unit for converting a three-phase grid voltage and a three-phase inverter current into a dq-axis voltage and a dq-axis current in a dq synchronous rotating coordinate system through coordinate transformation. ### Claim 20 (depends on 19) The inverter according to claim 19, wherein in the three-phase inverter, the voltage control unit further takes the output of the voltage loop as a d-axis current reference and sets a q-axis current reference to be a preset value. ### Claim 21 (depends on 15) The inverter according to claim 15, wherein the controller sends the relay control signal to turn on the relay after the current error is less than an error threshold value. ### Claim 22 (depends on 14) The inverter according to claim 14, wherein the threshold value is set to be greater than a maximum normal inverter current when the relay is turned off. ### Claim 23 (depends on 13) The inverter according to claim 13, wherein the virtual current calculating unit calculates the virtual current based on the following formula: l v = ( V e - V g ) Z v , wherein Iv is the virtual current, Ve is the output voltage of the controller, Vg is the grid voltage, and Zv is the virtual impedance. ### Claim 24 (depends on 13) The inverter according to claim 13, wherein the controller sends the relay control signal to turn on the relay after a delay time.