Method and apparatus for improved burst mode during power conversion

• US 8,492,932 B1
• Filed: 09/14/2012
• Issued: 07/23/2013
• 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:
  US13/615,920
• Time in Patent Office: 312 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 converting DC input power to AC output power. The apparatus comprises an input capacitor, a DC-AC inverter, a burst mode controller for causing energy to be stored in the input capacitor during at least one storage period and the energy to be drawn from the input capacitor during at least one burst period, wherein the AC output power is greater than the DC input power during the at least one burst period; a first feedback loop for determining a maximum power point (MPP) and operating the DC-AC inverter proximate the MPP; and a second feedback loop for determining a difference in a first power measurement and a second power measurement, producing an error signal indicative of the difference, and coupling the error signal to the first feedback loop to adjust at least one operating parameter of the DC-AC inverter to drive toward the MPP.

Claims

1. A method for converting DC input power into AC output power comprising:

operating in a continuous mode, while the DC input power is at a first level, wherein the DC input power is continuously converted into the AC output power and applied to an AC power grid; and

upon detecting the DC input power is at a second level, operating in a burst mode, wherein a burst of AC output power is followed by a period of no output power generation and an amount of AC output power for the burst is computed before applying the computed amount of AC output power to the AC power grid.

2. The method of claim 1 further comprising maximum power point tracking to substantially maintain the DC input power at a maximum amount during both the continuous and burst modes.

3. The method of claim 1 wherein, during the burst mode, determining a number of AC grid voltage cycles, N_off, that no output power is generated.

4. The method of claim 3 wherein N_off is less than

C*V_dc*V_r/P_in*T

where

C is the capacitance of an energy storage capacitor;

V_dc is an input voltage;

V_r is a burst mode ripple voltage;

P_in is the DC input power; and

T is an AC grid voltage cycle period.

5. The method of claim 3 wherein the amount of AC output power during the burst is a function N_off.

6. The method of claim 1 wherein, during the period of no output power, energy is stored in a storage device.

7. The method of claim 6 wherein the storage device is a capacitor.

8. The method of claim 7 further comprising minimizing a ripple voltage across the capacitor.

9. Apparatus for converting DC input power into AC output power comprising:

at least one controller for causing the apparatus to operate in a continuous mode while the DC input power is at a first level and operate in a burst mode while the DC input power is at a second level;

wherein, during the continuous mode, the DC input power is continuously converted into the AC output power and applied to an AC power grid and, during the burst mode, a burst of AC output power is followed by a period of no output power generation and an amount of AC output power for the burst is computed before applying the computed amount of AC output power to the AC power grid.

10. The apparatus of claim 9 further comprising a maximum power point tracking controller for substantially maintaining the DC input power at a maximum amount during both the continuous mode and the burst mode.

11. The apparatus of claim 9 further comprising an energy storage device for storing energy during the period of no output power generation.

12. The apparatus of claim 11 wherein the energy storage device is a capacitor.

13. A power generator comprising:

a photovoltaic panel for generating a DC input power; and

an inverter for converting the DC input power into AC output power comprising at least one controller for causing the inverter to operate in a continuous mode while the DC input power is at a first level and operate in a burst mode while the DC input power is at a second level;

wherein, during the continuous mode, the DC input power is continuously converted into the AC output power and applied to an AC power grid and, during the burst mode, a burst of AC output power is followed by a period of no output power generation and an amount of AC output power for the burst is computed before applying the computed amount of AC output power to the AC power grid.

14. The power generator of claim 13 further comprising a maximum power point tracking controller for substantially maintaining the DC input power at a maximum amount during both the continuous mode and the burst mode.

15. The power generator of claim 13 further comprising an energy storage device for storing energy during the period of no output power generation.

16. The power generator of claim 15 wherein the energy storage device is a capacitor.