Method and apparatus for improved burst mode during power conversion

• US 10,193,347 B2
• Filed: 03/29/2013
• Issued: 01/29/2019
• Est. Priority Date: 03/29/2013
• Status: Active Grant

• Current Assignee: Enphase Energy Incorporated
• Original Assignee: Enphase Energy Incorporated
• Inventors: Fornage, Martin
• Primary Examiner(s): Tran, Nguyen
• Assistant Examiner(s): Mata, Monica
• Application Number:
  US13/853,239
• Publication Number:
  US 20140293669A1
• Time in Patent Office: 2,132 Days
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources maximum power point systems in particular G05F1/67
• 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 inverter 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 the DC-AC inverter in a first burst mode, wherein during the first burst mode a first period of energy storage is immediately followed by a burst of AC output current generated for half of a particular grid cycle and immediately followed by a second period of energy storage, wherein each of the first and the second periods of energy storage lasts an integer number of grid voltage periods during which the DC-AC inverter does not generate any output power.

2. The method of claim 1 wherein each of the first and the second periods of energy storage 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 to be generated by the DC-AC inverter during the burst, 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 AC output current from the DC-AC inverter.

4. The method of claim 1 further comprising automatically alternating the polarity of subsequent bursts of AC output current following the burst of AC output current.

5. The method of claim 1 further comprising:

calculating the current to be generated by the DC-AC inverter during a burst when operating in a second burst mode as I_req*(2*N_off+1); and

operating the DC-AC inverter in the second burst mode, wherein, when operating in the second burst mode, each energy storage period lasts N_off AC grid voltage cycles, 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 AC output current from the DC-AC inverter.

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. An apparatus for converting DC input power into AC output power comprising:

a DC-AC inverter comprising at least one controller for causing the DC-AC inverter 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 first period of energy storage is immediately followed by a burst of AC output current generated for half of a particular grid cycle and immediately followed by a second period of energy storage, wherein each of the first and the second periods of energy storage lasts an integer number of grid voltage periods during which the DC-AC inverter does not generate any output power.

9. The apparatus of claim 8 wherein each of the first and the second periods of energy storage 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 to be generated by the DC-AC inverter during the burst, 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 AC output current from the DC-AC inverter.

11. The apparatus of claim 8 wherein the polarity of subsequent bursts of AC output current following the burst of AC output current automatically alternates.

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

calculating the current to be generated by the DC-AC inverter during a burst when operating in a second burst mode as I_req*(2*N_off+1); and

operating the DC-AC inverter in the second burst mode, wherein, when operating in the second burst mode, each energy storage period lasts N_off 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, and wherein I_req is a required AC output current from the DC-AC inverter.

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. A 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 first period of energy storage is immediately followed by a burst of AC output current generated for half of a particular grid cycle and immediately followed by a second period of energy storage, wherein each of the first and the second periods of energy storage lasts an integer number of grid voltage periods during which the inverter does not generate any output power.

16. The system of claim 15 wherein each of the first and the second periods of energy storage 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 to be generated by the inverter during the burst, 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 AC output current from the inverter.

18. The system of claim 15 wherein the polarity of subsequent bursts of AC output current following the burst of AC output current automatically alternates.

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

calculating the current to be generated by the inverter during a burst when operating in a second burst mode as I_req*(2*N_off+1); and

operating the inverter in the second burst mode, wherein, when operating in the second burst mode, each energy storage period lasts N_off AC grid voltage cycles, 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 AC output current from the inverter.

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 inverter; and

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