Technologies for interleaved control of an inverter array

• US 9,467,063 B2
• Filed: 11/29/2010
• Issued: 10/11/2016
• Est. Priority Date: 11/29/2010
• Status: Expired due to Fees

• Current Assignee: Enphase Energy Incorporated
• Original Assignee: Sunpower Corporation (Totalenergies Se)
• Inventors: Krein, Philip
• Primary Examiner(s): Nguyen, Matthew
• Assistant Examiner(s): DANG, TRINH Q
• Application Number:
  US12/955,894
• Publication Number:
  US 20120134189A1
• Time in Patent Office: 2,143 Days
• Field of Search: 323/272, 323/282, 323/299, 323/283, 323/268, 323/265, 323/271, 363/109, 363/15, 363/34, 363/71, 363/132, 363/89, 363/49, 363/55, 363/50, 307/80, 307/82
• US Class Current: 1/1
• CPC Class Codes: H02M 7/42 Conversion of dc power input into ac power output without possibility of reversal
• CPC Class Codes: H02M 7/49 Combination of the output voltage waveforms of a plurality of converters
• CPC Class Codes: H02M 7/51 using discharge tubes only

Abstract

An apparatus to deliver an alternating current (AC) power may include a controller having a processor and a memory. The apparatus may also include a plurality of power inverters in communication with the controller. Each power inverter may be configured to convert direct-current (DC) power into the (AC) power. Each of the plurality of power inverters may be configured to be controlled by the controller to generate AC power below at least one predetermined operating threshold. The plurality of power inverters may be configured to combine AC power generated by each of the plurality of power inverters, such that the combined AC power is delivered to a common AC load above the predetermined operating threshold. The apparatus may be arranged and operated according to a ratio of FMA=F_r/N, where Fr=f_s/f_l, f_s is the switching frequency of the plurality of power inverters, f_l is the frequency of the common AC load, and N is the number of power inverters of the apparatus.

Claims

1. A power inverter configured to receive power from a photovoltaic panel comprising a plurality of solar cells and to deliver an alternating current (AC) power, at a first frequency, fu, to a power grid, the power inverter comprising:

a controller having a processor and a memory;

an input converter having (i) an input configured to receive a DC input from the photovoltaic panel and (ii) an output coupled to a DC power bus, the input converter configured to supply a DC output to the DC power bus;

an output converter (i) having an input coupled to the DC power bus and (ii) configured to deliver the AC power at an AC output; and

an active filter electrically connected to the DC power bus and in communication with the controller, the active filter comprising;

at least two switching converters electrically coupled in parallel at a first common node and a second common node, wherein each switching converter of the at least two switching converters includes;

a first switch having a first terminal electrically coupled to the first common node and a second terminal electrically coupled to an internal node of the corresponding switching converter;

a second switch having a first terminal electrically coupled to the internal node and a second terminal electrically coupled to the second common node; and

at least one corresponding energy storage device electrically coupled to the internal node,

wherein each said switching converter is configured to supply a first AC power with a fundamental frequency at twice the first frequency to and absorb a second AC power with a fundamental frequency at twice the first frequency from the DC power bus using the at least one corresponding energy storage device of the corresponding switching converter,

wherein each of the first switch and the second switch is configured to operate in a series of switching cycles during which the relative timing and duration of the on and off times of each of the first switch and the second switch is configured to be controlled by the controller to control the AC power delivered by each said switching converter, and

wherein the controller is configured to control the switching cycles of the at least two plurality of switching converters to be interleaved with respect to one another.

2. The power inverter of claim 1, wherein each said switching converter is operated at a ratio of FMA=Fr/N that is less than four, wherein fu is the first frequency, wherein fs is a switching frequency for each said switching converter, and wherein Fr=fs/(2*fu) is a normalized switching frequency of the plurality of switching converters and N is a number of switching converters.

3. The power inverter of claim 1, wherein each switching converter of the plurality of switching converters receives power from a single corresponding DC source.

4. The power inverter of claim 1, wherein each said switching converter is configured to operate in a tri-level pulse width modulation (PWM) mode of operation.

5. The power inverter of claim 2, wherein FMA is less than 1.

6. The power inverter of claim 2, wherein Fr is greater than one and less than fifty.

7. The power inverter of claim 2, wherein Fr is greater than one and less than three.

8. The power inverter of claim 3, wherein the single corresponding DC source is a photovoltaic (PV) module comprising a number M PV cells and the power inverter comprises a number N switching converters.

9. The power inverter of claim 8, wherein M equals seventy-two.

10. The power inverter of claim 9, wherein N equals seventy-two.

11. An apparatus configured to deliver an alternating current (AC) power at a first frequency to a power grid, the apparatus comprising:

a controller having a processor and memory;

a photovoltaic panel comprising a plurality of solar cells; and

a plurality of power inventers in communication with the controller, wherein each power inverter of the plurality of power inverters includes a direct current (DC) input connected to a different subset of solar cells of the plurality of solar cells and comprises an active filter connected to a DC power bus of the corresponding power inverter, each active filter comprising;

at least two switching converters electrically coupled in parallel at a first common node and a second common node, wherein each switching converter of the at least two switching converters includes;

a first switch having a first terminal electrically coupled to the first common node and a second terminal electrically coupled to an internal node of the corresponding switching converter;

a second switch having a first terminal electrically coupled to the internal node and a second terminal electrically coupled to the second common node; and

at least one corresponding energy storage device electrically coupled to the internal node,

wherein each switching converter is configured to supply a first AC power with a fundamental frequency at twice the first frequency to and absorb a second AC power with a fundamental frequency at twice the first frequency from the DC power bus using the at least one corresponding energy storage device of the corresponding switching converter,

wherein each of the first switch and the second switch is configured to operate in a series of switching cycles, the duration of which defines a switching period and a switching frequency for the corresponding switching converter and is configured to be controlled by the controller to control the AC power delivered by each said switching converter; and

wherein the controller is configured to control the switching cycles of the at least two switching converters to be interleaved with respect to one another.

12. The apparatus of claim 11, wherein each power inverter of the plurality of power inverters comprises:

an input converter having an input configured to receive a DC input from the corresponding different subset of solar cells and an output coupled to the DC power bus, the input converter configured to supply a DC output to the DC power bus; and

an output converter having an input coupled to the DC power bus and configured to deliver the AC power at an AC output.

13. The apparatus of claim 11, wherein each of the first switch and the second switch is configured to operate in a series of switching cycles during which the relative timing and duration of the on and off times of each switch of the first switch and the second switch is configured to be controlled by the controller to control AC power delivered by each switching converter.

14. The apparatus of claim 11, wherein each said power inverter has the DC current input connected to a different solar cell of the plurality of solar cells.

15. The apparatus of claim 11, wherein the controller and the first switch and the second switch of each of the at least two switching converters are incorporated in an integrated circuit.

16. The apparatus of claim 11, wherein each said power inverter is configured to be a current-sourcing inverter for delivering a fraction of a total AC current delivered to the power grid.

17. The apparatus of claim 11, wherein each said switching converter is configured to operate in a tri-level pulse width modulation (PWM) mode of operation.

18. The apparatus of claim 11, wherein each said switching converter is operated at a ratio of FMA=Fr/N that is less than four, wherein fu is the first frequency of current delivered by each switching converter, fs is the switching frequency, Fr=fs/(2*fu) is a normalized switching frequency of the switching converters, and N is a number of switching converters included in the active filter.

19. The apparatus of claim 11, wherein N is a number of switching converters included in the active filter, T is the switching period, and the controller is configured to control the plurality of inverters to stagger a beginning of each successive switching cycle to occur substantially T/N seconds after a beginning of a preceding switching cycle of the switching converters.

20. The apparatus of claim 16, wherein each power inverter delivers a substantially equal fraction of the total AC current delivered to the power grid.

21. A method of operating a plurality of power inverters each of which is a direct current (DC)-alternating current (AC) power inverter to deliver an AC power at a first frequency to a power grid, the method comprising:

receiving, by each power inverter of the plurality of power inverters, a corresponding DC input from a corresponding subset of solar cells of a photovoltaic panel, wherein each power inverter comprises an active filter connected to a DC power bus of the corresponding power inverter, wherein each active filter comprises at least two switching converters electrically coupled in parallel at a first common node and a second common node, wherein each switching converter of the at least two switching converters comprises (i) a first switch having a first terminal electrically coupled to the first common node and a second terminal electrically coupled to an internal node of the corresponding switching converter, (ii) a second switch having a first terminal electrically coupled to the internal node and a second terminal electrically coupled to the second common node, and (iii) at least one energy storage device electrically coupled to the internal node; and

controlling switching cycles of an active filter of each said power inverter in an interleaved manner to supply a first AC power with a fundamental frequency at twice the first frequency to and absorb a second AC power with a fundamental frequency at twice the first frequency from a corresponding DC power bus of a corresponding power inverter using the at least one energy storage device of the corresponding active filter,

wherein each of the first switch and the second switch is configured to operate in a series of switching cycles, the duration of which defines a switching period and a switching frequency for the corresponding switching converter and is configured to be controlled by the controller to control the AC power delivered by each said switching converter.

22. The method of claim 21, further comprising providing a combined AC output of the plurality of power inverters to the power grid.

23. The method of claim 21, wherein controlling the switching cycles of the active filter further comprises sequentially controlling a beginning of a switching cycle in said each power inverter to occur at a different time during the operating period of the plurality of power inverters, such that each switching cycle is to occur substantially at 1/(fs*N) seconds after a beginning of a preceding switching cycle, wherein fs is the switching frequency and N is a number of power inverters included in the plurality of power inverters.

24. The method of claim 21, wherein the plurality of power inverters are embodied as an array of power inverters.

25. The method of claim 21, wherein controlling the switching cycles of the active filter comprises operating the switching converters in a tri-level pulse width modulation (PWM) mode of operation.

26. The method of claim 22, wherein providing the combined AC output comprises controlling each said power inverter to deliver substantially a same amount of power to the power grid as each other said power inverter.