Photovoltaic power conditioning units

• US 10,141,745 B2
• Filed: 12/12/2016
• Issued: 11/27/2018
• Est. Priority Date: 11/01/2011
• Status: Active Grant

• Current Assignee: Tesla Inc.
• Original Assignee: Tesla Inc.
• Inventors: Garrity, Paul, Mumtaz, Asim
• Primary Examiner(s): PATEL, RAJNIKANT B
• Application Number:
  US15/375,586
• Publication Number:
  US 20170093164A1
• Time in Patent Office: 715 Days
• Field of Search: 363 16, 363 34, 363 37, 363 39, 363 41, 363 71, 363 95, 363 97, 363127, 363132, 307 31, 307 35, 307 43, 307 77, 307 82, 307 87
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• 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: H02J 3/40 Synchronising a generator for connection to a network or to another generator
• CPC Class Codes: H02M 3/285 Single converters with a plurality of output stages connected in parallel parallel operation of a plurality of converters in dc distribution networks H02J1/10
• CPC Class Codes: H02M 5/458 using semiconductor devices only
• CPC Class Codes: H02M 7/46 using discharge tubes without control electrode or semiconductor devices without control electrode
• 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

We describe a photovoltaic (PV) panel system comprising a PV panel with multiple sub-strings of connected solar cells in combination with a power conditioning unit (microinverter). The power conditioning unit comprises a set of input power converters, one connected to each sub-string, and a common output power conversion stage, to provide power to an ac mains power supply output. Integration of the micro-inverter into the solar PV module in this way provides many advantages, including greater efficiency and reliability. Additionally, embodiments of the invention avoid the need for bypass diodes, a component with a high failure rate in PV panels, providing lower power loss and higher reliability.

Claims

1. A photovoltaic (PV) system comprising:

a PV module including a plurality of sub-strings of series connected solar cells arranged in loops; and

a plurality of series coupled conversion stages coupled to a DC link, each conversion stage coupled to a respective one of the plurality of sub-strings and including a DC output, one or more bypass diodes and a sub-string level Maximum Power Point Tracking (MPPT) circuit;

wherein each MPPT circuit includes a control circuit that adjusts a DC output voltage of one or more of the conversion stages to maintain a DC link voltage above a peak AC mains voltage.

2. The PV system of claim 1, wherein each conversion stage of the plurality of conversion stages includes a voltage-increasing DC-to-DC power converter.

3. The PV system of claim 1, wherein the one or more bypass diodes includes two diodes connected in parallel.

4. The PV system of claim 1, wherein MPPT is performed by monitoring current and voltage for each sub-string of the plurality of sub-strings.

5. The PV system of claim 1 further comprising a sub-string sensing system and at least one input power converter controller coupled to the sub-string sensing system to control a level of power conversion of one or more of the plurality of conversion stages responsive to a voltage of one of the plurality of sub-strings.

6. A photovoltaic (PV) system for delivering power to an AC grid, the PV system comprising:

a PV panel comprising a plurality of sub-strings of series connected solar cells, each sub-string of the plurality of sub-strings having an electrical connection at either end;

a set of series connected input power converters, one coupled to each sub-string of the plurality of sub-strings, wherein each input power converter includes one or more bypass diodes, a Maximum Power Point Tracking (MPPT) circuit and an output coupled to a common DC link; and

a common output power conversion stage coupled to the common DC link and configured to provide power to the AC grid;

wherein each MPPT circuit includes a control circuit that adjusts a DC output voltage of one or more of the input power converters to maintain a voltage of the common DC link above a peak AC grid voltage.

7. The PV system of claim 6, wherein each input power converter of the set of input power converters includes a voltage-increasing DC-to-DC converter.

8. The PV system of claim 6, wherein the common output power conversion stage includes a DC-to-AC converter that converts DC voltage received from the common DC link to AC power delivered to the AC grid.

9. The PV system of claim 8, wherein outputs of each of each input power converter of the set of input power converters are coupled to the common DC link.

10. The PV system of claim 6, wherein the one or more bypass diodes includes two diodes connected in parallel.

11. The PV system of claim 6, wherein MPPT is performed by monitoring current and voltage for each sub-string of the plurality of sub-strings.

12. The PV system of claim 6 further comprising a sub-string sensing system and at least one input power converter controller coupled to the sub-string sensing system to control a level of power conversion of one or more of the set of input power converters responsive to a voltage of one of the plurality of sub-strings.

13. A method of providing power to an AC grid from a photovoltaic (PV) panel, the PV panel comprising a plurality of sub-strings of series connected solar cells, the method comprising:

receiving, with a conversion stage, power from each sub-string of the plurality of sub-strings, wherein the conversion stage includes one or more bypass diodes and a sub-string level Maximum Power Point Tracking (MPPT) circuit;

combining power from a plurality of series connected conversion stages and conducting the combined power on a common DC bus;

adjusting a DC output voltage of one or more of the plurality of series connected conversion stages to maintain a voltage of the common DC bus above a peak AC grid voltage; and

converting, using a DC to AC converter, the combined power on the common DC bus to AC power for delivery to the AC grid.

14. The method of claim 13, wherein the conversion stage includes a voltage-increasing DC-to-DC power converter.

15. The method of claim 13, wherein DC outputs of each of the plurality of conversion stages are coupled to the common DC bus.

16. The method of claim 13, wherein the one or more bypass diodes includes two diodes connected in parallel.

17. The method of claim 13, wherein MPPT is performed by monitoring current and voltage for each sub-string of the plurality of sub-strings.

18. The method of claim 13 further comprising a sub-string sensing system and at least one input power converter controller coupled to the sub-string sensing system to control a level of power conversion of one or more of the plurality of conversion stages responsive to a voltage of one of the plurality of sub-strings.