Photovoltaic voltage regulation

• US 9,184,594 B2
• Filed: 06/03/2011
• Issued: 11/10/2015
• Est. Priority Date: 06/03/2011
• Status: Active Grant

• Current Assignee: Schneider Electric Solar Inverters Usa, Inc. (Schneider Electric SE)
• Original Assignee: Schneider Electric Solar Inverters Usa, Inc. (Schneider Electric SE)
• Inventors: Garabandic, Djordje
• Primary Examiner(s): Cavallari, Daniel
• Application Number:
  US13/152,787
• Publication Number:
  US 20120306279A1
• Time in Patent Office: 1,621 Days
• Field of Search: 307/85
• US Class Current: 1/1
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02S 40/32 comprising DC/AC inverter means associated with the PV module itself, e.g. AC modules
• CPC Class Codes: H02S 40/34 comprising specially adapted electrical connection means to be structurally associated with the PV module, e.g. junction boxes
• CPC Class Codes: H02S 50/00 Monitoring or testing of PV systems, e.g. load balancing or fault identification
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A photovoltaic system includes: a photovoltaic generator comprising strings that each includes one or more photovoltaic cells; a power converter; switches; and a controller. The power converter is configured to convert direct current (DC) power provided by the photovoltaic generator into alternating current (AC) power, and to output the AC power. Each switch is associated with one of the strings and is configured to connect the associated string to the power converter when set to a first setting, such that power generated by the first string can flow to the power converter. Each switch is also configured to disconnect the string from the power converter when set to a second setting. The controller is configured to control the power provided by the photovoltaic generator by selectively connecting the strings of the photovoltaic generator to the power converter by controlling the settings of the switches.

Claims

1. A photovoltaic system comprising:

a photovoltaic generator comprising a plurality of strings, each string comprising one or more photovoltaic cells;

a power converter configured to;

convert direct current (DC) power provided by the photovoltaic generator into alternating current (AC) power; and

output the AC power;

a plurality of switches, each switch being associated with one of the plurality of strings and being configured to connect the associated string to the power converter when set to a first setting such that power generated by the first string can flow to the power converter, each switch being further configured to disconnect the string from the power converter when set to a second setting; and

a controller configured to control the power provided by the photovoltaic generator by selectively connecting the plurality of strings of the photovoltaic generator to the power converter by controlling the settings of the plurality of switches, wherein the controller is further configured to

receive an inverter startup signal indicating that the power converter is in a startup period during which power provided by the photovoltaic generator is to be gradually ramped up,

disconnect any strings in excess of strings used to provide startup voltage, and

iteratively connect strings to gradually increase power provided by the photovoltaic generator.

2. The system of claim 1 wherein the controller is configured to monitor the voltage of a power sink, and wherein the controller is configured to decrease the power provided by the photovoltaic generator to the power converter by selectively disconnecting strings of the photovoltaic generator in response to a decrease in voltage of the power sink.

3. The system of claim 2 wherein the controller is configured to increase the power provided by the photovoltaic generator to the power converter by selectively connecting strings of the photovoltaic generator in response to an increase voltage of the power sink.

4. A photovoltaic system comprising:

a photovoltaic generator comprising a plurality of strings, each string comprising one or more photovoltaic cells;

a power converter configured to;

convert direct current (DC) power provided by the photovoltaic generator into alternating current (AC) power; and

output the AC power;

a plurality of switches, each switch being associated with one of the plurality of strings and being configured to connect the associated string to the power converter when set to a first setting such that power generated by the first string can flow to the power converter, each switch being further configured to disconnect the string from the power converter when set to a second setting; and

a controller configured to control the power provided by the photovoltaic generator by selectively connecting the plurality of strings of the photovoltaic generator to the power converter by controlling the settings of the plurality of switches, wherein the controller is configured to monitor the voltage of a power sink, and wherein the controller is configured to decrease the power provided by the photovoltaic generator to the power converter by selectively disconnecting strings of the photovoltaic generator in response to a decrease in voltage of the power sink, wherein the controller further comprises

a tangible, non-transitory computer-readable memory;

a plurality of modules comprising processor executable code stored in the memory;

a processor connected to the memory and configured to access the plurality of modules stored in the memory; and

a control interface configured to send control signals to the plurality of switches;

wherein the plurality of modules stored in the memory includes;

a voltage control module configured to cause the processor to;

monitor the voltage of the power sink to identify changes in the voltage of the power sink; and

determine whether to connect or disconnect one or more strings of the photovoltaic generator, to adjust the power provided by the photovoltaic generator, in response to a change in voltage of the power sink;

a string selection module configured to cause the processor to select one or more strings of the photovoltaic generator in response to be connected or disconnected based on a determination by the voltage control module that one or more strings of the photovoltaic generator should be connected or disconnected in response to a change in voltage of the power sink; and

a control signal module configured to cause the processor to send control signals to the switches to cause the one or more strings to be connected to the power converter or to be disconnected from the power converter.

5. A system for controlling the power output of a photovoltaic system, the photovoltaic system including a photovoltaic generator that comprises a plurality of strings, each string comprising one or more photovoltaic cells, the system comprising:

means for receiving an inverter startup signal indicating that a power converter of the photovoltaic system is in a startup period during which power provided by the photovoltaic generator is to be gradually ramped up;

means for disconnecting any strings in excess of strings used to provide startup voltage; and

means for iteratively connecting strings to gradually increase power provided by the photovoltaic generator.

6. The system of claim 5 wherein each string is associated with a switch, and wherein the means for disconnecting any strings in excess of strings used to provide startup voltage further comprises means for sending a control signal to each of the switches associated with each of the strings to be disconnected to disconnect the strings from the power converter.

7. The system of claim 6 wherein the means for connecting the strings to adjust the photovoltaic voltage provided by the photovoltaic generator further comprises means for sending a control signal to each of the switches associated with each of the strings to be connected to connect the strings to the power converter.

8. A system for controlling the power output of a photovoltaic system, the photovoltaic system including a photovoltaic generator that comprises a plurality of strings, each string comprising one or more photovoltaic cells, the system comprising:

means for monitoring a voltage of a power sink associated with the photovoltaic system;

means for determining whether the voltage of the power sink has decreased, and in response to the voltage of the power sink decreasing;

means for calculating a percentage of the voltage of the power sink relative to a nominal level associated with the power sink, the nominal level representing a desired voltage level for the power sink;

means for calculating a number strings of the photovoltaic generator to be disconnected to decrease a photovoltaic voltage provided by the photovoltaic generator, wherein disconnecting the string prevents power generated by the string from reaching a power converter of the photovoltaic system that converts direct current (DC) power to alternating current (AC) power expected by the power sink;

means for disconnecting the calculated number of strings to adjust the photovoltaic voltage provided by the photovoltaic generator.

9. The system of claim 8, further comprising:

means for determining whether the voltage of the power sink has increased, and in response to the voltage of the power sink increasing;

means for calculating a percentage of the voltage of the power sink relative to a nominal level associated with the power sink, the nominal level representing a desired voltage level for the power sink;

means for calculating a number strings of the photovoltaic generator to be connected to decrease a photovoltaic voltage provided by the photovoltaic generator, wherein connecting the string allows power generated by the string to reach the power converter of the photovoltaic system; and

means for connecting the calculated number of strings to increase the photovoltaic voltage provided by the photovoltaic generator.

10. The system of claim 9 further comprising:

means for reducing the voltage of the photovoltaic generator by an amount proportional to the decrease in voltage of the power sink responsive to the voltage of the power sink decreasing responsive to a low voltage ride through (LVRT) event.

11. The system of claim 9 further comprising:

means for increasing the voltage provided by the photovoltaic generator by an amount proportional to the increase in voltage of the power sink responsive to the voltage of the power sink increasing responsive to a low voltage ride through (LVRT) event.

12. The system of claim 9 wherein each string is associated with a switch, and wherein the means for disconnecting the calculated number of strings to adjust the photovoltaic voltage provided by the photovoltaic generator further comprises means for sending a control signal to the switches associated with each of the strings to be disconnected to disconnect the strings from the power converter.

13. The system of claim 12 wherein the means for connecting the calculated number of strings to adjust the photovoltaic voltage provided by the photovoltaic generator further comprises means for sending a control signal to the switches associated with each of the strings to be connected to connect the strings to the power converter.

14. A system for controlling the power output of a photovoltaic system, the photovoltaic system including a photovoltaic generator that comprises a plurality of strings, each string comprising one or more photovoltaic cells, comprising:

means for determining a voltage of a power sink associated with the photovoltaic system;

means for determining a reference voltage for the photovoltaic generator, the reference voltage representing a desired voltage for the photovoltaic generator;

means for determining a current voltage for the photovoltaic generator;

means for determining a difference between the reference voltage and the current voltage;

means for calculating a number of strings of the photovoltaic generator to connect or disconnect based on the difference, wherein disconnecting the string prevents power generated by the string from reaching a power converter of the photovoltaic system that converts direct current (DC) power to alternating current (AC) power expected by the power sink, and wherein connecting the string allows power generated by the string to reach the power converter of the photovoltaic system; and

means for connecting or disconnecting the calculated number of strings to adjust the photovoltaic voltage provided by the photovoltaic generator.

15. The system of claim 14 wherein each string is associated with a switch, and wherein the means for disconnecting the strings to adjust the photovoltaic voltage provided by the photovoltaic generator comprises means for sending a control signal to the switches associated with each of the strings to be disconnected to disconnect the strings from the power converter.

16. The system of claim 15 wherein the means for connecting the strings to adjust the photovoltaic voltage provided by the photovoltaic generator comprises means for sending a control signal to the switches associated with each of the strings to be connected to connect the strings to the power converter.