Inter coupling of microinverters

• US 10,148,093 B2
• Filed: 06/16/2015
• Issued: 12/04/2018
• Est. Priority Date: 06/16/2015
• Status: Active Grant

• Current Assignee: Koolbridge Solar, Inc.
• Original Assignee: Koolbridge Solar, Inc.
• Inventors: Dent, Paul Wilkinson
• Primary Examiner(s): Johnson, Ryan
• Application Number:
  US14/740,972
• Publication Number:
  US 20160372927A1
• Time in Patent Office: 1,267 Days
• CPC Class Codes: H01L 31/0504 specially adapted for series or parallel connection of solar cells in a module
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02M 1/0077 Plural converter units whose outputs are connected in series
• CPC Class Codes: H02M 1/123 Suppression of common mode voltage or current
• CPC Class Codes: H02M 1/126 using passive filters
• CPC Class Codes: H02M 7/49 Combination of the output voltage waveforms of a plurality of converters
• CPC Class Codes: H02M 7/537 using semiconductor devices only, e.g. single switched pulse inverters
• CPC Class Codes: H02S 40/32 comprising DC/AC inverter means associated with the PV module itself, e.g. AC modules
• CPC Class Codes: H02S 40/34 comprising specially adapted electrical connection means to be structurally associated with the PV module, e.g. junction boxes
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A number of DC-AC microinverters driven by separate photovoltaic sub-arrays are physically combined to use common components such as a common, common-mode choke. Each microinverter is controlled by a common switching controller to produce a portion of the desired output such that ripple on the combined output is minimized, and each microinverter produces a common mode signal on its associated sub-array equal in frequency to the desired AC output frequency.

Claims

1. A DC to AC inverter arrangement for converting Direct Current (DC) power from photovoltaic sub-arrays to Alternating Current (AC) power of a desired AC output voltage or current at output terminals and having a sinusoidal waveform of a desired frequency comprising:

a number of substantially identical microinverters combined in the same mechanical housing, each microinverter being configured to be powered from a respective photovoltaic sub-array via a positive and a negative DC input terminal, and configured so that the positive and negative input terminals from each sub-array get connected through a common mode filter comprising a common-mode choke to the positive and negative terminals of an associated smoothing capacitor, the positive and negative terminals of the smoothing capacitor also being connected to the positive and negative inputs of an associated H-bridge configuration of switching transistors, at least one output of each H-bridge being connected through a low pass filter to attenuate switching frequency components and to obtain a corresponding filtered H-bridge output across the microinverter output terminals, wherein one output terminal of at least a first microinverter is connected to a first output terminal of the inverter and one output terminal of at least a second microinverter is connected to a second output terminal of the inverter, and wherein the other output terminals of the microinverters are connected in parallel, series, or series parallel configuration;

a common switching controller configured to control the switching of each H-bridge in each of said microinverters to connect a first output terminal of each H-bridge via an appropriate switching transistor of the H-bridge alternately at said desired AC output frequency to the positive and the negative H-bridge inputs from the respective terminals of said associated smoothing capacitor while controlling a second output of each H-bridge to connect via another appropriate switching transistor of the H-bridge alternately to the same or opposite polarity H-bridge input at a high switching frequency with a duty factor chosen so as to provide an effective mean value equal to a point on said sinusoidal waveform;

wherein the outputs of said microinverters are combined at the inverter outputs to provide said desired voltage or current having said sinusoidal waveform; and

wherein said common mode choke is a multifilar common mode choke having 2M mutually insulated parallel windings, each pair of windings being used to connect the positive and negative terminals of a sub-array to the associated microinverter'"'"'s smoothing capacitor and H-bridge, thereby sharing the same common mode choke among a number M of microinverters.

2. The arrangement of claim 1 whereby said common switching controller controls said high frequency switching of each of said microinverter'"'"'s H-bridge'"'"'s second output terminals to the same or opposite polarity H-bridge input using a switching clock phase that is staggered across all microinverters so as to achieve reduction of as many dominant ripple components as possible at said combined output.

3. The arrangement of claim 1 in which said microinverter outputs are combined in series at said combined output.

4. The arrangement of claim 1 in which said microinverter outputs are combined in parallel at said combined output.

5. The arrangement of claim 1 in which said microinverter outputs are combined in a series parallel combination.

6. The arrangement of claim 1 in which a first of said microinverters generates a first approximately sinusoidal waveform at a first output voltage at its second output terminal relative to its first output terminal and a second of said microinverters generates a second approximately sinusoidal waveform at a second output voltage at its second output terminal relative to its first output terminal, the second approximately sinusoidal waveform being in antiphase with the first approximately sinusoidal waveform, and the outputs of said first and second microinverters are constructively combined in series by connecting the first output terminals of both microinverters together to obtain a combined approximately sinusoidal waveform of voltage equal to the sum of said first output voltage and said second output voltage between the second output terminals of said first and second microinverters.

7. The arrangement of claim 1 in which a first of said microinverters generates a first approximately sinusoidal waveform at a first output voltage at its second output terminal relative to its first output terminal and a second of said microinverters generates a second approximately sinusoidal waveform at a second output voltage at its second output terminal relative to its first output terminal, the second approximately sinusoidal waveform being in antiphase with the first approximately sinusoidal waveform, and the outputs of said first and second microinverters are constructively combined in series by connecting the second output terminals of both microinverters together to obtain a combined approximately sinusoidal waveform of voltage equal to the sum of said first output voltage and said second output voltage between the first output terminals of said first and second microinverters.

8. The arrangement of claim 1 in which said combined output at said output terminals is connected to an electricity grid and said microcontroller controls said voltage and current to cause a desired power flow from said DC to AC inverter arrangement into said electricity grid.

9. The arrangement of claim 1 in which said output terminals are connected to the L1 and antiphase L2 of a 120/240 v 60 Hz split phase utility grid and each microinverter'"'"'s positive and negative input terminals for DC from its respective sub-array are decoupled to grid neutral with a capacitor, the connection to neutral being interruptible by means of a output relay.

10. The arrangement of claim 1, further comprising:

the number of substantially identical microinverters comprise at least one pair of associated microinverters, wherein a first microinverter of each pair is powered by DC from a respective first sub-array of photovoltaic cells and the second microinverter of each pair is powered by a respective second photovoltaic sub-array of photovoltaic cells, and the first and second sub-arrays of cells are interleaved in a pattern such that groups of cells associated with a first microinverter of each pair of microinverters are physically located between groups of cells associated with second microinverters of each pair of microinverters;

the common switching controller controls said first and second microinverters so that said first microinverters generate a sinusoidal voltage or current output of a first phase and said second microinverters generate a sinusoidal voltage or current output in antiphase to said first phase; and

wherein the outputs of said first and second microinverters are constructively combined in parallel by reversing the output terminals of the antiphase second inverters relative to the output terminals of the first inverters in order to obtain said AC power output of desired voltage or current and frequency, or alternatively the outputs are constructively combined in series by connecting a terminal of an antiphase second converter to a corresponding terminal of a first inverter.

11. The arrangement of claim 1 wherein said switching controller is configured to control the H-bridges of a first subset of said microinverters to produce a common mode signal on their respective positive and negative input terminals of frequency equal to said desired AC output frequency and of a first phase and to control the H-bridges of a second subset of said microinverters to produce a common mode signal on their respective positive and negative input terminals of frequency equal to said desired AC output frequency and of a second phase in antiphase to said first phase.

12. The arrangement of claim 1 wherein said switching controller is configured to control the H-bridges of a first subset of said microinverters to produce a common mode signal on their respective positive and negative input terminals of frequency equal to said desired AC output frequency and of a first phase and to control the H-bridges of a second subset of said microinverters to produce a common mode signal on their respective positive and negative input terminals of frequency equal to said desired AC output frequency and of a second phase in antiphase to said first phase, and said common mode choke is a multifilar common mode choke having pairs of parallel windings equal in number to the number of microinverters, and said positive and negative input terminals of said first subset of microinverters connect to a first end of their assigned windings of said multifilar common mode choke while said positive and negative input terminals of said second subset of microinverters connect to an end of their assigned windings opposite to said first end.

13. A method of DC to AC conversion for converting Direct Current power from a photovoltaic array to Alternating Current power of a desired AC output voltage or current at output terminals and having a sinusoidal waveform of a desired frequency comprising:

configuring a number of substantially identical DC to AC converting microinverters each to receive a portion of said Direct Current power from a separate, electrically isolated, sub-array section of said photovoltaic array and each generating a portion of said desired output voltage or current at an associated pair of output terminals;

controlling said microinverters with a common controller such that the portion of said desired AC output voltage or current produced by a first subset of said microinverters is in antiphase at corresponding pairs of output terminals with the portion of the desired AC voltage or current produced by a second subset of said microinverters; and

combining the outputs of said microinverters in series or parallel or series-parallel such that either their corresponding portions of the said desired AC output voltage add constructively or their corresponding portions of said desired AC output current add constructively or both their voltage and current portions add constructively.

14. The method of claim 13 wherein said number of microinverters is equal to M, the Direct Current voltage from each of said sub-array sections of said photovoltaic array is approximately 1/Mth of the square root of 2 times said desired AC output voltage, and said output terminal pairs of said M microinverters are connected in series in such a way that their contributions to said desired AC output voltage add constructively.

15. The method of claim 13 in which controlling said microinverters with a common controller comprises:

controlling the switching of an H-bridge of switching transistors of each of said first subset of microinverters, the H-bridge being connected to the DC input from the corresponding sub-array section, such that the DC positive and negative inputs are alternately connected to a first of said output terminal pairs of said first of microinverters at said desired output frequency while the second of said output terminal pairs is connected alternately to said positive or negative DC input at a high switching frequency and with a duty factor that gives a mean value equal to a point on said desired sinusoidal waveform; and

controlling the switching of an H-bridge of switching transistors of each of said second subset of microinverters, the H-bridge being connected to the DC input from the corresponding sub-array section, such that the respective DC positive inputs of each of said second subset of microinverters is connected to a first of said output terminal pairs of said second subset of microinverters when the respective DC negative inputs of said first subset of microinverters are connected to the first of their respective output terminal pairs, and such that the respective DC negative inputs of each of said second subset of microinverters is connected to the first of said output terminal pairs of said second subset of microinverters when the respective DC positive inputs of said first subset of microinverters are connected to the first of their respective output terminal pairs.

16. The method of claim 13 in which controlling said microinverters with a common controller comprises:

controlling the switching of an H-bridge of switching transistors of each of said microinverters, the H-bridge being connected to the DC input from the corresponding sub-array section, such that the DC positive and negative inputs are alternately connected to a first of said output terminal pairs of said microinverters at said desired output frequency while the second of said output terminal pairs is connected alternately to said positive or negative DC input at a high switching clock frequency and with a duty factor that gives a mean value equal to a point on said desired sinusoidal waveform; and

staggering the timing of said high frequency switching clock between different microinverters such that, when their outputs are combined, the greatest number of switching frequency related spectral components are substantially canceled.

17. The method of claim 13 wherein the step of configuring a number of substantially identical DC to AC converting microinverters each to receive a portion of said Direct Current power from a separate, electrically isolated, sub-array section of said photovoltaic array comprises coupling the negative and positive polarity connections from each sub-array DC input through an assigned pair of mutually insulated windings of a common, multifilar, common-mode choke to the associated microinverter, wherein the sub-array inputs of said first subset of microinverters connect to a first end of their assigned pairs of said multifilar windings and the sub-array inputs of said second subset of microinverters connect to a second end opposite to said first end of the multifilar winding pairs assigned to the second subset of microinverters.

18. The method of claim 13 in which controlling said microinverters with said common controller results in a common mode signal appearing on each associated sub-array section of said photovoltaic array when operating, the common mode signal being equal in frequency to said desired AC output frequency.

19. The method of claim 13 in which controlling said microinverters with said common controller results in a common mode signal appearing on the associated sub-array section of said photovoltaic array when operating, the common mode signal being a square wave combined with a sinewave equal in frequency to said desired AC output frequency.

20. A DC to AC inverter arrangement for converting Direct Current (DC) power from photovoltaic sub-arrays to Alternating Current (AC) power of a desired AC output voltage or current at output terminals and having a sinusoidal waveform of a desired frequency comprising:

a number of substantially identical microinverters combined in the same mechanical housing, each microinverter being configured to be powered from a respective photovoltaic sub-array via a positive and a negative DC input terminal, and configured so that the positive and negative input terminals from each sub-array get connected through a common mode filter comprising a common-mode choke to the positive and negative terminals of an associated smoothing capacitor, the positive and negative terminals of the smoothing capacitor also being connected to the positive and negative inputs of an associated H-bridge configuration of switching transistors, at least one output of each H-bridge being connected through a low pass filter to attenuate switching frequency components and to obtain a corresponding filtered H-bridge output across the microinverter output terminals, wherein one output terminal of at least a first microinverter is connected to a first output terminal of the inverter and one output terminal of at least a second microinverter is connected to a second output terminal of the inverter, and wherein the other output terminals of the microinverters are connected in parallel, series, or series parallel configuration;

a common switching controller configured to control the switching of each H-bridge in each of said microinverters to connect a first output terminal of each H-bridge via an appropriate switching transistor of the H-bridge alternately at said desired AC output frequency to the positive and the negative H-bridge inputs from the respective terminals of said associated smoothing capacitor while controlling a second output of each H-bridge to connect via another appropriate switching transistor of the H-bridge alternately to the same or opposite polarity H-bridge input at a high switching frequency with a duty factor chosen so as to provide an effective mean value equal to a point on said sinusoidal waveform;

wherein the outputs of said microinverters are combined at the inverter outputs to provide said desired voltage or current having said sinusoidal waveform; and

wherein said common switching controller controls said high frequency switching of each of said microinverter'"'"'s H-bridge'"'"'s second output terminals to the same or opposite polarity H-bridge input using a switching clock phase that is staggered across all microinverters so as to achieve reduction of as many dominant ripple components as possible at said combined output.

21. The arrangement of claim 20 in which said common mode choke is a multifilar common mode choke having 2M mutually insulated parallel windings, each pair of windings being used to connect the positive and negative terminals of a sub-array to the associated microinverter'"'"'s smoothing capacitor and H-bridge, thereby sharing the same common mode choke among a number M of Microinverters.

22. The arrangement of claim 20 in which said microinverter outputs are combined in series at said combined output.

23. The arrangement of claim 20 in which said microinverter outputs are combined in parallel at said combined output.

24. The arrangement of claim 20 in which said microinverter outputs are combined in a series parallel combination.

25. The arrangement of claim 20 in which a first of said microinverters generates a first approximately sinusoidal waveform at a first output voltage at its second output terminal relative to its first output terminal and a second of said microinverters generates a second approximately sinusoidal waveform at a second output voltage at its second output terminal relative to its first output terminal, the second approximately sinusoidal waveform being in antiphase with the first approximately sinusoidal waveform, and the outputs of said first and second microinverters are constructively combined in series by connecting the first output terminals of both microinverters together to obtain a combined approximately sinusoidal waveform of voltage equal to the sum of said first output voltage and said second output voltage between the second output terminals of said first and second microinverters.

26. The arrangement of claim 20 in which a first of said microinverters generates a first approximately sinusoidal waveform at a first output voltage at its second output terminal relative to its first output terminal and a second of said microinverters generates a second approximately sinusoidal waveform at a second output voltage at its second output terminal relative to its first output terminal, the second approximately sinusoidal waveform being in antiphase with the first approximately sinusoidal waveform, and the outputs of said first and second microinverters are constructively combined in series by connecting the second output terminals of both microinverters together to obtain a combined approximately sinusoidal waveform of voltage equal to the sum of said first output voltage and said second output voltage between the first output terminals of said first and second microinverters.

27. The arrangement of claim 20 in which said combined output at said output terminals is connected to an electricity grid and said microcontroller controls said voltage and current to cause a desired power flow from said DC to AC inverter arrangement into said electricity grid.

28. The arrangement of claim 20 in which said output terminals are connected to the L1 and antiphase L2 of a 120/240 v 60 Hz split phase utility grid and each microinverter'"'"'s positive and negative input terminals for DC from its respective sub-array are decoupled to grid neutral with a capacitor, the connection to neutral being interruptible by means of a output relay.

29. The arrangement of claim 20, further comprising:

the number of substantially identical microinverters comprise at least one pair of associated microinverters, wherein a first microinverter of each pair is powered by DC from a respective first sub-array of photovoltaic cells and the second microinverter of each pair is powered by a respective second photovoltaic sub-array of photovoltaic cells, and the first and second sub-arrays of cells are interleaved in a pattern such that groups of cells associated with a first microinverter of each pair of microinverters are physically located between groups of cells associated with second microinverters of each pair of microinverters;

the common switching controller controls said first and second microinverters so that said first microinverters generate a sinusoidal voltage or current output of a first phase and said second microinverters generate a sinusoidal voltage or current output in antiphase to said first phase; and

wherein the outputs of said first and second microinverters are constructively combined in parallel by reversing the output terminals of the antiphase second inverters relative to the output terminals of the first inverters in order to obtain said AC power output of desired voltage or current and frequency, or alternatively the outputs are constructively combined in series by connecting a terminal of an antiphase second converter to a corresponding terminal of a first inverter.