Maximizing power in a photovoltaic distributed power system
A power harvesting system including multiple parallel-connected photovoltaic strings, each photovoltaic string includes a series-connection of photovoltaic panels. Multiple voltage-compensation circuits may be connected in series respectively with the photovoltaic strings. The voltage-compensation circuits may be configured to provide respective compensation voltages to the photovoltaic strings to maximize power harvested from the photovoltaic strings. The voltage-compensation circuits may be include respective inputs which may be connected to a source of power and respective outputs which may be connected in series with the photovoltaic strings.
1. A system comprising:
a plurality of parallel-connected photovoltaic strings, each photovoltaic string comprising:
a photovoltaic string having a series-connection of photovoltaic panels; and
a voltage-compensation circuit configured to produce an output power having an adjustable compensation voltage; and
a controller configured to:
monitor power and adjust the adjustable compensation voltage of each voltage-compensation circuit until a net total power is maximized;
wherein a plurality of first values are the adjustable compensation voltages for each of the voltage-compensation circuits,
wherein a second value is a minimum compensation voltage of the adjustable compensation voltages; and
for each adjustable compensation voltage, adjust the adjustable compensation voltage to a new voltage value, wherein the new voltage value is the second value subtracted from the first value.
2. The system of claim 1 , wherein the plurality of parallel-connected photovoltaic strings are connected between terminals of a direct current (DC) bus.
3. The system of claim 1 , wherein the controller is configured to operate in each iteration of a control algorithm.
4. The system of claim 1 , further comprising a sensor configured to sense a power on a direct current (DC) bus connected to the plurality of parallel connected photovoltaic strings.
5. The system of claim 1 , wherein the controller is configured to determine an input of the voltage-compensation circuit from at least one electrical parameter related to a direct current (DC) bus connected to the plurality of parallel connected photovoltaic strings.
6. The system of claim 1 , wherein each voltage-compensation circuit comprises an input connected to an alternating current (AC) power grid.
7. The system of claim 1 , wherein the net total power is one of:
a power sensed by a sensor minus the power derived from an independent alternating current (AC) or direct current (DC) source if a power input to the voltage-compensation circuits is derived from the independent alternating current (AC) or direct current (DC) source; or
a power sensed by the sensor if a power input to the voltage-compensation circuits is derived from a DC bus.
8. The system of claim 1 , wherein the controller is connected to each voltage-compensation circuit.
9. The system of claim 1 , further comprising:
a sensor connected to an output of the plurality of the parallel-connected photovoltaic strings and to the controller, wherein the sensor is configured to sense a power at the output of the plurality of the parallel-connected photovoltaic strings and provide the sensed power to the controller.
10. The system of claim 1 , wherein each voltage-compensation circuit comprises an alternating current (AC) to direct current (DC) converter, wherein the AC to DC converter includes an input connected to a source of power of the respective voltage-compensation circuit, and wherein the AC to DC converter includes an output configured to provide the adjustable compensation voltage.
11. The system of claim 1 , wherein each voltage-compensation circuit comprises a direct current (DC) to DC converter, wherein the DC to DC converter includes an input connected to a source of power of the respective voltage-compensation circuit, and wherein the DC to DC converter includes an output configured to provide the adjustable compensation voltage.
12. The system of claim 1 , further comprising:
an inverter having an input attached to an output of the plurality of parallel-connected photovoltaic strings.
13. The system of claim 12 , wherein the inverter has an output configured to provide a source of power to each voltage-compensation circuit, and the net total power is sensed by a sensor.
14. The system of claim 1 , wherein an output terminal of the voltage-compensation circuit is connected to a terminal of one of the photovoltaic panels.
15. The system of claim 1 , wherein the controller is configured to track power produced from the plurality of parallel-connected photovoltaic strings.
16. A method comprising:
performing by a controller:
monitoring power at an output of a plurality of parallel-connected photovoltaic strings, wherein each photovoltaic string of the plurality of parallel-connected photovoltaic strings comprises one or more photovoltaic panels connected in series with a voltage-compensation circuit having an adjustable compensation voltage at its output;
adjusting the adjustable compensation voltage of each voltage-compensation circuit until a net total power is maximized, wherein a plurality of first values are the adjustable compensation voltages, each first value corresponding to one of the adjustable compensation voltages, wherein a second value is a minimum compensation voltage of the adjustable compensation voltages; and
adjusting each of the adjustable compensation voltages to a new voltage value, wherein the new voltage value is the second value subtracted from the first value.
17. The method of claim 16 , wherein the net total power is one of:
a power sensed by a sensor minus a power derived from an independent alternating current (AC) or direct current (DC) source if a power input to the voltage-compensation circuits is derived from the independent alternating current (AC) or direct current (DC) source; or
a power sensed by the sensor if a power input to the voltage-compensation circuits is derived from a DC bus.
18. The method of claim 16 , wherein a sensor is connected to an output of the plurality of parallel-connected photovoltaic strings and to the controller, and the sensor is configured to sense a power at the output of the plurality of parallel-connected photovoltaic strings and provide the sensed power to the controller.
19. The method of claim 16 , wherein:
an input of each voltage-compensation circuit is connected to a source of power independent from power provided by a corresponding photovoltaic string, and
the adjustable compensation voltage is generated from outputs of a converter receiving the source of power at inputs of the converter.
20. The method of claim 16 , wherein each voltage-compensation circuit comprises an input connected to an alternating current (AC) power grid.
21. The method of claim 16 , wherein an input of an inverter is connected to an output of the plurality of parallel-connected photovoltaic strings, and wherein an output of the inverter is configured to provide a source of power to each voltage-compensation circuit, and the net total power is sensed by a sensor.
22. The method of claim 16 , wherein:
the controller is connected to each voltage-compensation circuit;
the controller is configured to track power produced from the plurality of parallel-connected photovoltaic strings;
the plurality of parallel-connected photovoltaic strings are connected between terminals of a direct current (DC) bus;
an output terminal of the voltage-compensation circuit is connected to a terminal of one of the photovoltaic panels; and
the controller is configured to operate in each iteration of a control algorithm.