METHOD AND APPARATUS FOR IMPROVED BURST MODE DURING POWER CONVERSION

• US 20140293669A1
• Filed: 03/29/2013
• Published: 10/02/2014
• Est. Priority Date: 03/29/2013
• Status: Active Grant

• Current Assignee: Enphase Energy Incorporated
• Original Assignee: Enphase Energy Incorporated
• Inventors: Fornage, Martin
• Granted Patent: US 10,193,347 B2
• Time in Patent Office: Days
• US Class Current: 363/95
• 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 1/0035 using burst mode control
• CPC Class Codes: H02M 7/48 using discharge tubes with control electrode or semiconductor devices with control electrode
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

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 DC input power is continuously converted into 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 for a half grid cycle is followed by a period of energy storage lasting an integer number of grid cycles.

Claims

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

operating a DC-AC converter in a continuous mode, while the DC input power is at a first level, wherein during the continuous mode the DC input power is continuously converted into 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 first burst mode, wherein during the first burst mode a burst of AC output power for a half grid cycle is followed by a period of energy storage lasting an integer number of grid cycles.

2. The method of claim 1 wherein the energy storage period is for ((N_off/2) rounded up to the nearest integer) AC grid voltage cycles, wherein N_off is the number of grid cycles of energy storage for bursting for a full grid-cycle.

3. The method of claim 2 further comprising calculating the current generated by the DC-AC inverter during the first burst mode, I_B, as I_req*(2*(new N_off)+1) wherein new N_off=((N_off/2) rounded up to the nearest integer), and wherein I_req is a required inverter AC output current.

4. The method of claim 1 further comprising automatically alternating the polarity of the burst of AC output power over a plurality of grid cycles.

5. The method of claim 1 further comprising:

calculating the current generated by the DC-AC inverter during a second burst mode, I_B, as I_req*(2*N_off+1); and

limiting the DC-AC inverter to operating in the second burst mode with an energy storage period of N_off, wherein N_off is the number of grid cycles of energy storage for bursting for a full grid-cycle, and wherein I_req is a required inverter AC output current.

6. The method of claim 5 further comprising:

selecting the first burst mode if I_req is greater than a maximum rating for the DC-AC inverter; and

selecting the second burst mode if I_req is not greater than the maximum rating for the DC-AC inverter.

7. The method of claim 5 further comprising selecting a burst mode from the first or the second burst mode based on the burst mode which harvests a greater amount of energy.

8. 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 first 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 AC output power and applied to an AC power grid and, during the first burst mode, a burst of AC output power for a half grid cycle is followed by a period of energy storage lasting an integer number of grid cycles.

9. The apparatus of claim 8 wherein the energy storage period is for ((N_off/2) rounded up to the nearest integer) AC grid voltage cycles, wherein N_off is the number of grid cycles of energy storage when AC output power is burst for a full grid-cycle.

10. The apparatus of claim 9 wherein the at least one controller is further configured for calculating the current generated by the DC-AC inverter during the first burst mode, I_B, as I_req*(2*(new N_off)+1), wherein new N_off=N_off/2 rounded up to the nearest integer), and wherein I_req is a required inverter AC output current.

11. The apparatus of claim 8 wherein the at least one controller is further configured for automatically alternating the polarity of the burst of AC output power over a plurality of grid cycles.

12. The apparatus of claim 8 wherein the at least one controller is further configured for:

calculating the current generated by the DC-AC inverter during a second burst mode, I_B, as I_req*(2*N_off+1); and

limiting the DC-AC inverter to operating in the second burst mode with an energy storage period of N_off, wherein N_off is the number of grid cycles of energy storage when AC output power is burst for a full grid-cycle, and wherein I_req is a required inverter AC output current.

13. The apparatus of claim 12 wherein the at least one controller is further configured for:

selecting the first burst mode if I_req is greater than a maximum rating for the DC-AC inverter; and

selecting the second burst mode if I_req is not greater than the maximum rating for the DC-AC inverter.

14. The apparatus of claim 12 wherein the at least one controller is further configured for selecting a burst mode from the first or the second burst mode based on the burst mode which harvests a greater amount of energy.

15. System for converting DC input power into AC output power comprising:

a photovoltaic (PV) module for providing the DC input power; and

an inverter, coupled to the PV module, comprising at least one controller for operating the inverter in a continuous mode while the DC input power is at a first level and operating the inverter in a first 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 AC output power and applied to an AC power grid and, during the first burst mode, a burst of AC output power for a half grid cycle is followed by a period of energy storage lasting an integer number of grid cycles.

16. The system of claim 15 wherein the energy storage period is for ((N_off/2) rounded up to the nearest integer) AC grid voltage cycles, wherein N_off is the number of grid cycles of energy storage when AC output power is burst for a full grid-cycle.

17. The system of claim 16 wherein the at least one controller is further configured for calculating the current generated by the DC-AC inverter during the first burst mode, I_B, as I_req*(2*(new N_off)+1), wherein new N_off=((N_off/2) rounded up to the nearest integer), and wherein I_req is a required inverter AC output current.

18. The system of claim 15 wherein the at least one controller is further configured for automatically alternating the polarity of the burst of AC output power over a plurality of grid cycles.

19. The system of claim 15 wherein the at least one controller is further configured for:

calculating the current generated by the DC-AC inverter during a second burst mode, I_B, as I_req*(2*N_off+1); and

limiting the DC-AC inverter to operating in the second burst mode with an energy storage period of N_off, wherein N_off is the number of grid cycles of energy storage when AC output power is burst for a full grid-cycle, and wherein I_req is a required inverter AC output current.

20. The system of claim 19 wherein the at least one controller is further configured for:

selecting the first burst mode if I_req is greater than a maximum rating for the DC-AC inverter; and

selecting the second burst mode if I_req is not greater than the maximum rating for the DC-AC inverter.