Inverters

• US 8,674,548 B2
• Filed: 09/23/2011
• Issued: 03/18/2014
• Est. Priority Date: 01/18/2011
• Status: Active Grant

• Current Assignee: Tesla Inc.
• Original Assignee: Enecsys Limited
• Inventors: Mumtaz, Asim
• Primary Examiner(s): KAPLAN, HAL IRA
• Application Number:
  US13/244,226
• Publication Number:
  US 20120056484A1
• Time in Patent Office: 907 Days
• Field of Search: 307/85, 307/86, 307/109
• US Class Current: 307/86
• CPC Class Codes: H01L 31/02021 for solar cells electrical connection means, e.g. junction boxes, specially adapted for structural association with photovoltaic modules H02S40/34
• CPC Class Codes: H02H 7/16 for capacitors for synchronous capacitors H02H7/06
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 3/00 Circuit arrangements for ac mains or ac distribution networks
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/46 Controlling of the sharing of output between the generators, converters, or transformers
• CPC Class Codes: H02M 7/44 by static converters
• CPC Class Codes: H02M 7/48 using discharge tubes with control electrode or semiconductor devices with control electrode
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

We describe a photovoltaic power conditioning unit for delivering power from multiple photovoltaic panels to an ac mains power supply output, comprising: a dc input for receiving power from multiple photovoltaic panels; an ac output for delivering ac power to the ac supply; a bank of electrolytic energy storage capacitors for storing energy from the dc source for delivery to the ac supply; a dc-to-ac converter coupled to the ac output and having an input coupled to the bank for converting energy stored in the bank to ac power for the ac supply; and further comprising: a plurality of sense and control circuits, one for each capacitor in the bank, wherein each circuit is coupled in series with a capacitor, and is configured to disconnect the associated capacitor from the bank upon detection of a current flow thorough the associated capacitor of greater than a threshold current value.

Claims

1. A photovoltaic power conditioning unit for delivering power from one or more photovoltaic panels to an ac mains power supply, the power conditioning unit comprising:

a dc input for receiving power from said one or more photovoltaic panels;

an ac output for delivering ac power to said ac mains power supply;

a bank of electrolytic energy storage capacitors for storing energy from said dc input for delivering to said ac mains power supply;

a dc-to-ac converter coupled to said ac output and having an input coupled to said bank of electrolytic energy storage capacitors for converting energy stored in said bank of electrolytic energy storage capacitors to ac power for said ac mains power supply; and

a plurality of sense and control circuits, one for each of said electrolytic energy storage capacitors of said bank of electrolytic energy storage capacitors, wherein each of said sense and control circuits is coupled in series with an associated energy storage capacitor of said bank, and wherein each of said sense and control circuits is configured to disconnect the associated electrolytic energy storage capacitor from said bank of capacitors upon detection of a current flow through the associated electrolytic energy storage capacitor of greater than a threshold current value that is set according to a number of electrolytic energy storage capacitors in the bank.

2. The photovoltaic power conditioning unit of claim 1, wherein said threshold current value is determined by

3. The photovoltaic power conditioning unit of claim 1, wherein said sense and control circuit comprises a senseFET.

4. The photovoltaic power conditioning unit of claim 1, wherein said sense and control circuit comprises a fuse, and wherein said disconnection is dependent upon a time-averaged square of a current flowing onto or off said bank of energy storage capacitors.

5. The photovoltaic power conditioning unit of claim 1, wherein said sense and control circuit comprises a low-pass filter in a sense-control loop of said sense and control circuit to attenuate a high frequency component from switching of said dc-to-ac converter when sensing said current flow through the associated energy storage capacitor.

6. The photovoltaic power conditioning unit of claim 5, wherein said low-pass filter has a corner frequency of at least 1 KHz.

7. The photovoltaic power conditioning unit of claim 1, wherein a single energy storage capacitor of said bank has a capacitance which is sufficient for an ac ripple voltage component at a frequency of said ac mains power supply not to pull an instantaneous voltage on said bank below zero when said power conditioning unit is operating at a maximum rated ac output power.

8. The photovoltaic power conditioning unit of claim 1, wherein said bank of electrolytic energy storage capacitors further comprises one or more non-electrolytic energy storage capacitors, such that said bank comprises a mixture of electrolytic and non-electrolytic energy storage capacitors.

9. The photovoltaic power conditioning unit of claim 1 further comprising a capacitor technology control circuit coupled to one or more of said sense and control circuits to control selective connection of said electrolytic energy storage capacitors to an internal bus of said capacitor bank for use within said bank.

10. The photovoltaic power conditioning unit of claim 9, wherein said capacitor technology control circuit controls the selective connection of each said electrolytic energy storage capacitor of said bank, the photovoltaic power conditioning unit further comprising at least one temperature sensor, wherein said selective connection of each electrolytic energy storage capacitor comprises disconnection of the electrolytic energy storage capacitor when a temperature sensed by said temperature sensor is beyond a threshold temperature value.

11. The photovoltaic power conditioning unit of claim 9, wherein said selective connection of each electrolytic energy storage capacitor comprises disconnection of the electrolytic energy storage capacitor during a start-up period of said power conditioning unit.

12. The photovoltaic power conditioning unit of claim 1 further comprising a dc-to-dc converter coupled between said dc input and said bank of electrolytic energy storage capacitors configured to increase a dc voltage from said one or more photovoltaic panels for said dc-to-ac converter.

13. The photovoltaic power conditioning unit of claim 1, wherein said power conditioning unit has a single power conversion stage.

14. The photovoltaic power conditioning unit of claim 1, wherein said power conditioning unit has a maximum rated ac output power of less than 600 W.

15. The photovoltaic power conditioning unit of claim 1, wherein said bank of electrolytic energy storage capacitors comprises less than 20 electrolytic energy storage capacitors.

16. A photovoltaic power conditioning unit for delivering power from one or more photovoltaic panels to an ac mains power supply, the power conditioning unit comprising:

a dc input for receiving power from said one or more photovoltaic panels;

an ac output for delivering ac power to said ac mains power supply;

at least two banks of electrolytic energy storage capacitors for storing energy from said dc input for delivering to said ac mains power supply;

a dc-to-ac converter coupled to said ac output and having an input coupled to said banks of electrolytic energy storage capacitors for converting energy stored in said banks of electrolytic energy storage capacitors to ac power for said ac mains power supply;

a plurality of sense and control circuits, one for each of said electrolytic energy storage capacitors of said banks of electrolytic energy storage capacitors, wherein each of said sense and control circuits is coupled in series with an associated energy storage capacitor of said banks, and wherein each of said sense and control circuits is configured to disconnect the associated electrolytic energy storage capacitor from said banks of capacitors upon detection of a current flow through the associated electrolytic energy storage capacitor of greater than a threshold current value; and

a capacitor bank control circuit to selectively connect one or other of said banks to said dc-to-ac converter.

17. The photovoltaic power conditioning unit of claim 16, wherein said capacitor bank control circuit is configured to time-multiplex use of said banks of electrolytic energy storage capacitors.

18. The photovoltaic power conditioning unit of claim 17, wherein said capacitor bank control circuit is further configured to avoid said time-multiplexed use of a particular bank responsive to detection that all said energy storage capacitors in the particular bank have failed.

19. A method of enhancing the reliability of a photovoltaic power conditioning unit for delivering power from one or more photovoltaic panels to an ac mains power supply, the power conditioning unit comprising:

a dc input for receiving power from said one or more photovoltaic panels;

an ac output for delivering ac power to said ac mains power supply;

a bank of electrolytic energy storage capacitors for storing energy from said dc input for delivering to said ac mains power supply; and

a dc-to-ac converter coupled to said ac output and having an input coupled to said bank of electrolytic energy storage capacitors for converting energy stored in said bank of electrolytic energy storage capacitors to ac power for said ac mains power supply;

the method comprising;

disconnecting an electrolytic energy storage capacitor from said bank of capacitors upon detection of a current flow through the electrolytic energy storage capacitor of greater than a threshold current value;

wherein said threshold current value is determined by