Method and apparatus for improved burst mode during power conversion

• US 8,035,257 B2
• Filed: 08/02/2010
• Issued: 10/11/2011
• Est. Priority Date: 10/10/2008
• Status: Active Grant

• Current Assignee: Enphase Energy Incorporated
• Original Assignee: Enphase Energy Incorporated
• Inventors: Fornage, Martin
• Primary Examiner(s): Deberadinis; Robert L.
• Application Number:
  US12/804,943
• Publication Number:
  US 20100309695A1
• Time in Patent Office: 435 Days
• Field of Search: 307/140
• US Class Current: 307/140
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02M 7/42 Conversion of dc power input into ac power output without possibility of reversal
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A method and apparatus for coupling power to an AC power grid. In one embodiment, the method comprises interleaving a storage period and a burst period, wherein (i) energy is stored during the storage period for a predetermined number of grid voltage cycles, and (ii) stored energy is converted to AC power and coupled to the AC power grid during the burst period.

Claims

1. A method for coupling power to an AC power grid, comprising:

interleaving a storage period and a burst period, wherein (i) energy is stored during the storage period for a predetermined number of grid voltage cycles, and (ii) stored energy is converted to AC power and coupled to the AC power grid during the burst period.

2. The method of claim 1, wherein the predetermined number of the grid voltage cycles is determined prior to the storage period such that a ripple voltage across a device storing the energy satisfies a voltage threshold.

3. The method of claim 1, further comprising:

generating a first power measurement and a second power measurement;

computing a power difference based on a difference between the first and the second power measurements; and

monitoring, based on the power difference, a maximum power point (MPP) of a power source providing power.

4. The method of claim 3, wherein the first power measurement is based on binning the power during a first period and the second power measurement is based on binning the power during a second period.

5. The method of claim 4, wherein the first period is a first portion of the storage period and the second period is a second portion of the storage period.

6. The method of claim 1, further comprising converting DC power received during the burst period to generate the AC power.

7. The method of claim 1, wherein the energy is stored during the storage period when power from a power source is less than optimal for continually coupling power to the AC power grid.

8. The method of claim 7, wherein the power is less than optimal when the power satisfies a power threshold.

9. The method of claim 1, wherein the predetermined number of the grid voltage cycles in the storage period is greater than one and the burst period is one grid voltage cycle.

10. The method of claim 2, wherein the predetermined number of the grid voltage cycles is less than C*Vdc*Vr/Pin, where C is a capacitance of the device, Vdc is an average voltage across a power source, Vr is a magnitude of the ripple voltage, and Pin is an input power from the power source.

11. An apparatus for coupling power to an AC power grid, comprising:

a capacitor for storing energy during a storage period of at least one grid voltage cycle of the AC power grid;

a burst mode controller coupled to the capacitor for controlling energy flow to and from the capacitor, wherein the burst mode controller computes a number of the grid voltage cycles in the storage period prior to the storage period; and

a DC-AC converter coupled to the capacitor for converting stored energy to AC power and coupling the AC power to the AC power grid during a burst period.

12. The apparatus of claim 11, wherein the burst mode controller computes the number of the grid voltage cycles such that a ripple voltage across the capacitor satisfies a voltage threshold.

13. The apparatus of claim 11, wherein the burst mode controller generates a first power measurement and a second power measurement, and wherein a power difference based on a difference between the first and the second power measurements is utilized for monitoring a maximum power point (MPP) of a power source providing power.

14. The apparatus of claim 13, wherein the first power measurement is based on binning the power during a first period and the second power measurement is based on binning the power during a second period.

15. The apparatus of claim 14, wherein the first period is a first portion of the storage period and the second period is a second portion of the storage period.

16. The apparatus of claim 11, wherein the DC-AC converter further converts DC power received during the burst period to generate the AC power.

17. The apparatus of claim 11, wherein the burst mode controller causes the energy to be stored when power from a power source is less than optimal for continually coupling power to the AC power grid.

18. The apparatus of claim 11, wherein the number of the grid voltage cycles in the storage period is greater than one and the burst period is one grid voltage cycle.

19. The apparatus of claim 12, wherein the number of the grid voltage cycles is less than C*Vdc*Vr/Pin, where C is a capacitance of the capacitor, Vdc is an average voltage across a power source, Vr is a magnitude of the ripple voltage, and Pin is an input power from the power source.

20. A system for coupling power to an AC power grid, comprising:

a photovoltaic (PV) module; and

an inverter coupled to the PV module, wherein the inverter comprises;

a capacitor for storing energy from the PV module during a storage period of at least one grid voltage cycle of the AC power grid;

a burst mode controller coupled to the capacitor for controlling energy flow to and from the capacitor, wherein the burst mode controller computes, prior to the storage period, a number of the grid voltage cycles in the storage period such that a ripple voltage across the capacitor satisfies a voltage threshold; and

a DC-AC converter coupled to the capacitor for converting stored energy to AC power and coupling the AC power to the power grid.