Serially connected inverters

• US 9,866,098 B2
• Filed: 06/12/2014
• Issued: 01/09/2018
• Est. Priority Date: 01/12/2011
• Status: Active Grant

• Current Assignee: Solaredge Technologies Incorporated
• Original Assignee: Solaredge Technologies Incorporated
• Inventors: Yoscovich, Ilan, Gazit, Meir, Glovinsky, Tzachi, Galin, Yoav
• Primary Examiner(s): Fureman, Jared
• Assistant Examiner(s): Barnett, Joel
• Application Number:
  US14/303,067
• Publication Number:
  US 20140292085A1
• Time in Patent Office: 1,307 Days
• Field of Search: 307 43, 307 63, 307 29, 307 54, 307 80, 307 77, 307 82, 307 85, 307 86, 307 87, 363 13, 363 16, 363 19, 363 71, 136244
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources maximum power point systems in particular G05F1/67
• CPC Class Codes: H02J 3/00 Circuit arrangements for ac mains or ac distribution networks
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/388 Islanding, i.e. disconnection of local power supply from the network
• CPC Class Codes: H02J 3/42 with automatic parallel connection when synchronisation is achieved
• CPC Class Codes: H02J 3/46 Controlling of the sharing of output between the generators, converters, or transformers
• CPC Class Codes: H02M 1/0077 Plural converter units whose outputs are connected in series
• CPC Class Codes: H02M 1/325 with means for allowing continuous operation despite a fault, i.e. fault tolerant converters
• CPC Class Codes: H02M 7/49 Combination of the output voltage waveforms of a plurality of converters
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A photovoltaic power generation system, having a photovoltaic panel, which has a direct current (DC) output and a micro-inverter with input terminals and output terminals. The input terminals are adapted for connection to the DC output. The micro-inverter is configured for converting an input DC power received at the input terminals to an output alternating current (AC) power at the output terminals. A bypass current path between the output terminals may be adapted for passing current produced externally to the micro-inverter. The micro-inverter is configured to output an alternating current voltage significantly less than a grid voltage.

Claims

1. A method, comprising:

connecting input terminals of a plurality of micro-inverters to direct current outputs of respective photovoltaic panels;

connecting output terminals of the plurality of micro-inverters serially to a serial voltage output, wherein the plurality of micro-inverters comprise respective bypass current paths comprising at least two switches connected between the output terminals of the respective one of the plurality of micro-inverters to form an alternate current path between the output terminals of the respective one of the plurality of micro-inverters;

inverting, with the plurality of micro-inverters, input direct current (DC) power received at the input terminals of each of the plurality of micro-inverters to output alternating-current (AC) power at the output terminals of the respective one of the plurality of micro-inverters while maintaining a serial voltage of the serial voltage output substantially equal to a grid voltage of a grid connected across the serial voltage output;

in response to determining a failure of one or more micro-inverters of the plurality of micro-inverters, bypassing the one or more micro-inverters by switching the at least two switches of the bypass current path of each of the one or more micro-inverters;

operating the plurality of micro-inverters in synchronization with the grid voltage; and

in response to determining a failure in operating at least one of the plurality of micro-inverters to be in synchronization with the grid voltage, bypassing the output terminals of the at least one of the plurality of micro-inverters by switching the at least two switches of the respective bypass current path and operating others of the plurality of micro-inverters to adjust the serial voltage to the grid voltage.

2. The method of claim 1, further comprising:

upon the connecting the input terminals and connecting the output terminals, enabling the inverting the input DC power after a previously determined time delay.

3. The method of claim 1, further comprising:

disconnecting the plurality of micro-inverters from the grid or disabling the plurality of micro-inverters in response to detecting at least one of the following conditions;

the serial voltage being less than the grid voltage, and a lack of synchronization between the serial voltage and the grid voltage.

4. The method of claim 3, wherein the disabling the plurality of micro-inverters comprises stopping transmitting of a “

keep alive”

signal.

5. The method of claim 3, wherein the disconnecting the plurality of micro-inverters from the grid comprises opening a switch connected between the plurality of micro-inverters and the grid.

6. The method of claim 1, wherein each of the plurality of micro-inverters comprises a control loop configured to maintain the input DC power received at the input terminals of a respective one of the plurality of micro-inverters at a maximum input power.

7. The method of claim 1, wherein the output AC power at the output terminals of each of the plurality of micro-inverters is at a voltage substantially less than the grid voltage.

8. A system comprising:

a plurality of micro-inverters, each micro-inverter of the plurality of micro-inverters having input terminals and output terminals,

wherein the output terminals of the plurality of micro-inverters are connected serially and configured to form a serial voltage output when the input terminals are connected to direct-current (DC) power from a photovoltaic panel;

wherein each micro-inverter of the plurality of micro-inverters is configured to invert the DC power received at the input terminals of the micro-inverter to output alternating-current (AC) power at the output terminals of the micro-inverter while maintaining a serial voltage of the serial voltage output substantially equal to and synchronized with a grid voltage of a grid when the grid is connected across the serial voltage output; and

wherein each micro-inverter of the plurality of micro-inverters further comprises a bypass current path comprising at least two switches connected between the output terminals of the micro-inverter to form an alternate current path between the output terminals of the micro-inverter, each micro-inverter of the plurality of micro-inverters is configured to bypass the output terminals by switching the at least two switches in response to determining a failure in operating the micro-inverter to be in synchronization with the grid voltage, and each micro-inverter of the plurality of micro-inverters is configured to adjust the serial voltage output to the grid voltage in response to a failure in operating a second micro-inverter to be in synchronization with the grid voltage.

9. The system of claim 8, further comprising a control unit configured to disconnect the plurality of micro-inverters from the grid or disable the plurality of micro-inverters in response to detecting at least one of the following conditions:

the serial voltage being less than the grid voltage, and a lack of synchronization between the serial voltage and the grid voltage.

10. The system of claim 9, further comprising a switch connected between the plurality of micro-inverters and the grid, wherein the control unit is configured to open the switch in response to detecting at least one of the following conditions:

the serial voltage being less than the grid voltage, and a lack of synchronization between the serial voltage and the grid voltage.

11. The system of claim 9, further comprising a switch connected between the plurality of micro-inverters and the grid, wherein the control unit is configured to send a “

keep alive”

signal to the plurality of micro-inverters, and the plurality of micro-inverters are configured to convert the DC power to the AC power in response to receiving the “

keep alive”

signal, and wherein the control unit is configured to open the switch in response to detecting at least one of the following conditions;

the serial voltage being less than the grid voltage, and a lack of synchronization between the serial voltage and the grid voltage.

12. The system of claim 8, wherein each of the plurality of micro-inverters comprises a control loop configured to maintain the DC power received at the input terminals at a maximum input power.

13. The system of claim 8, wherein each of the plurality of micro-inverters is configured to output AC power at the output terminals at a voltage substantially lower than the grid voltage.

14. An apparatus comprising a first micro-inverter, the first micro-inverter comprising:

input terminals;

output terminals configured to generate part of a serial voltage output that is formed when the input terminals are connected to direct-current (DC) power from a photovoltaic panel and one of the output terminals is connected an output terminal of a second micro-inverter;

wherein the first micro-inverter is configured to invert the DC power received at the input terminals to output alternating-current (AC) power at the output terminals of the first micro-inverter while maintaining, together with at least the second micro-inverter, the serial voltage output to be substantially equal to and synchronized with a grid voltage of a grid when the grid is connected across the serial voltage output; and

wherein the first micro-inverter further comprises a bypass current path comprising at least two switches connected between the output terminals of the first micro-inverter to form an alternate current path between the output terminals, and the first micro-inverter is configured to bypass the output terminals by switching the at least two switches in response to a failure in operating the first micro-inverter to be in synchronization with the grid voltage, and the first micro-inverter is configured to adjust the serial voltage output to the grid voltage in response to a failure in operating the second micro-inverter to be in synchronization with the grid voltage.

15. The apparatus of claim 14, wherein the first micro-inverter comprises a control loop configured to maintain the DC power received at the input terminals at a maximum input power.

16. The apparatus of claim 14, wherein the first micro-inverter is configured to output the AC power at the output terminals at a voltage substantially lower than the grid voltage.

17. The apparatus of claim 14, wherein the first micro-inverter is configured to convert the DC power to output the AC power in response to receiving a “

keep alive”

signal, and is configured to stop converting the DC power to output AC power in response to not receiving a “

keep alive”

signal for a predetermined period of time.

18. The apparatus of claim 14, wherein the first micro-inverter is converted to stop converting the DC power to output AC power in response to an absence of the grid.

19. The apparatus of claim 14, further comprising a control unit and a switch connected between the first micro-inverter and the grid, wherein the control unit is configured to disconnect the first micro-inverter from the grid by opening the switch in response to an islanding condition.

20. The apparatus of claim 19, wherein the control unit is configured to send a “

keep alive”

signal to the first micro-inverter to enable converting the DC power to output the AC power, and is configured to stop sending the “

keep alive”

signal to shut down the first micro-inverter.