Apparatus and method for controlling a power inverter

• US 8,817,510 B2
• Filed: 10/02/2012
• Issued: 08/26/2014
• Est. Priority Date: 10/11/2010
• Status: Active Grant

• Current Assignee: Enphase Energy Incorporated
• Original Assignee: Solarbridge Technologies Incorporated (Totalenergies Se)
• Inventors: Esram, Trishan, Gray, Alexander, Martina, Eric, Chapman, Patrick
• Primary Examiner(s): Zhang, Jue
• Application Number:
  US13/633,785
• Publication Number:
  US 20130027998A1
• Time in Patent Office: 693 Days
• Field of Search: 363/132.95, 363/17, 363/98, 363/132, 700/286, 700/298, 700/291
• US Class Current: 363/132
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• 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: H02J 3/44 with means for ensuring correct phase sequence
• CPC Class Codes: H02M 7/4807 having a high frequency intermediate AC stage
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

An apparatus and method for controlling a DC-to-AC inverter is disclosed. The DC-to-AC inverter may be configured to convert DC power received from an alternative energy source to AC power for supplying an AC grid or load. The inverter may determine whether the power presently supplied by the alternative energy source is less than a predetermined amount of power and, if so, disable an output converter of the inverter. Additionally, the inverter may predict the voltage of a DC bus of the inverter at a future point in time and, if the predicted DC bus voltage is greater than a predetermined maximum DC bus voltage, enable the output converter to transfer energy from the DC bus to the AC grid to reduce the DC bus voltage.

Claims

1. A direct current (DC)-to-alternating current (AC) inverter comprising:

an input converter having an input configured to receive a DC input power from a DC energy source;

an output converter having an AC output configured to supply an AC output power to an AC grid;

a DC bus coupled to the input converter and the output converter; and

a control circuit electrically coupled to the input converter and the output converter, wherein the control circuit is configured to;

disable the output converter in response to a determination that the DC input power of the DC-to-AC inverter is less than a first reference threshold;

determine an estimated future voltage of the DC bus based on a present voltage of the DC bus; and

enable, subsequent to the disablement of the output converter, the output converter in response to the determination that the estimated future voltage of the DC bus is greater than a second reference threshold.

2. The DC-to-AC inverter of claim 1, wherein to to determine the estimated future voltage comprises to determine an estimated voltage of the DC bus for a future reference point of a grid voltage or a grid current of the AC grid.

3. The DC-to-AC inverter of claim 2, wherein to determine the estimated voltage of the DC bus comprises to determine the estimated voltage of the DC bus based on the DC input power.

4. The DC-to-AC inverter of claim 2, wherein to enable the output converter comprises to:

determine a minimum DC bus voltage for the future reference point of the grid voltage or the grid current of the AC grid; and

transfer energy from the DC bus to the AC output to reduce the voltage of the DC bus to the minimum DC bus voltage.

5. The DC-to-AC inverter of claim 4, wherein to determine the minimum DC bus voltage comprises to determine a minimum DC bus voltage for the future reference point of the grid voltage or the grid current of the AC grid as a function of (i) the grid voltage of the AC grid and (ii) a DC voltage of the DC input power.

6. The DC-to-AC inverter of claim 1, wherein the control circuit is further configured to cycle the output converter between an enabled state and a disabled state while the DC input power is less than the first reference threshold to maintain a voltage of the DC bus between a minimum reference voltage and the first reference voltage.

7. The DC-to-AC inverter of claim 1, wherein the DC bus comprises a bus capacitor coupled to a DC output of the input converter and a DC input of the output converter.

8. A method for increasing the efficiency of a direct current (DC)-to-alternating current (AC) inverter, the method comprising:

disabling an AC output of the DC-to-AC inverter in response to a DC input power of the DC-to-AC inverter being less than a first reference threshold;

determining an estimated future voltage of a DC bus of the DC-to-AC inverter based on a present voltage of the DC bus; and

enabling, subsequent to disabling the AC output of the DC-to-AC inverter, the AC output in response to the estimated future voltage of the DC bus of the DC-to-AC inverter being greater than a second reference threshold.

9. The method of claim 8, wherein disabling the AC output of the DC-to-AC inverter comprises disabling a DC-to-AC output converter of the DC-to-AC inverter.

10. The method of claim 8, wherein determining the estimated future voltage of the DC bus comprises determining an estimated voltage of the DC bus for a future reference point of a grid voltage or a grid current of an AC grid coupled to the AC output.

11. The method of claim 10, wherein determining the estimated voltage of the DC bus comprises determining the estimated voltage of the DC bus based on the DC input power.

12. The method of claim 10, wherein enabling the AC output of the DC-to-AC inverter comprises:

determining a minimum DC bus voltage for the future reference point of the grid voltage or the grid current of the AC grid; and

transferring energy from the DC bus to the AC output to reduce the voltage of the DC bus to the minimum DC bus voltage.

13. The method of claim 12, wherein determining the minimum DC bus voltage comprises determining a minimum DC bus voltage for the future reference point of the grid voltage or the grid current of the AC grid as a function of (i) the grid voltage of the AC grid and (ii) a DC voltage of the DC input power.

14. The method of claim 8, further comprising cycling the AC output of the inverter between an enabled state and a disabled state while the DC input power of the DC-to-AC inverter is less than the first reference threshold to maintain a voltage of the DC bus of the inverter between a minimum reference voltage and the first reference voltage.

15. A direct current (DC)-to-alternating current (AC) inverter comprising:

an input converter having an input configured to receive a DC input power from a DC energy source;

an output converter having an AC output configured to supply an AC output power to an AC grid;

a DC bus coupled to the input converter and the output converter; and

a control circuit electrically coupled to the input converter and the output converter, wherein the control circuit is configured to (i) determine an estimated future voltage of the DC bus based on a present voltage of the DC bus and (ii) cycle the output converter between an enabled and a disabled state while the DC input power is less than a first reference threshold, wherein the output converter is cycled to the enabled state in response to the estimated future voltage of the DC bus being greater than a second reference threshold.

16. The DC-to-AC inverter of claim 15, wherein to determine the estimated future voltage of the DC bus comprises to determine an estimated voltage of the DC bus for a future reference point of a grid voltage or a grid current of the AC grid.

17. The DC-to-AC inverter of claim 16, wherein to determine the estimated voltage of the DC bus comprises to determine the estimated voltage of the DC bus based on the DC input power.

18. The DC-to-AC inverter of claim 16, wherein the control circuit is configured to:

determine a minimum DC bus voltage for the future reference point of the grid voltage or the grid current of the AC grid; and

cycle the output converter to the enabled state to transfer energy from the DC bus to the AC output to reduce the voltage of the DC bus to the minimum DC bus voltage in response to the estimated voltage of the DC bus being greater than the second reference threshold.

19. The DC-to-AC inverter of claim 18, wherein to determine the minimum DC bus voltage comprises to determine a minimum DC bus voltage for the future reference point of the grid voltage or the grid current of the AC grid as a function of (i) the grid voltage of the AC grid and (ii) a DC voltage of the DC input power.