Method and apparatus for determining a maximum power point of photovoltaic cells
First Claim
1. A method for determining a maximum power point (MPP) of a photovoltaic array, comprising at least one photovoltaic cell, coupleable to a power inverter by way of a DC bus comprising a capacitor coupled across the DC bus and a switch positioned between the photovoltaic array and an AC bus of the inverter, the method comprising:
- closing the switch and obtaining a maximum value of a current substantially provided by the photovoltaic array to the capacitor in response to the closing of the switch;
charging the capacitor with the current to progressively increase a voltage of the capacitor while the current decreases from the maximum value;
obtaining values of the current and the voltage while the capacitor is charging;
obtaining a value of the voltage after the capacitor is charged;
using the obtained maximum value of the current, the values of the current and the voltage while the capacitor is charging, and the value of the voltage after the capacitor is charged to generate I-V characteristics of the photovoltaic array; and
determining the MPP of the photovoltaic array from the generated I-V characteristics.
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Accused Products
Abstract
The maximum power point (MPP) of a photovoltaic array that can be coupled to power inverter is determined. A capacitor on a DC-bus side of the inverter is used as a load from which I-V characteristics of the photovoltaic array can be generated. The photovoltaic array is connected to the capacitor, which has been previously discharged by a bleed down resistor. Short circuit current, open circuit voltage, and values of current and voltage as the capacitor charges are determined and used to generate I-V characteristics of the photovoltaic array. From the I-V characteristics, the MPP can be calculated.
206 Citations
34 Claims
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1. A method for determining a maximum power point (MPP) of a photovoltaic array, comprising at least one photovoltaic cell, coupleable to a power inverter by way of a DC bus comprising a capacitor coupled across the DC bus and a switch positioned between the photovoltaic array and an AC bus of the inverter, the method comprising:
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closing the switch and obtaining a maximum value of a current substantially provided by the photovoltaic array to the capacitor in response to the closing of the switch;
charging the capacitor with the current to progressively increase a voltage of the capacitor while the current decreases from the maximum value;
obtaining values of the current and the voltage while the capacitor is charging;
obtaining a value of the voltage after the capacitor is charged;
using the obtained maximum value of the current, the values of the current and the voltage while the capacitor is charging, and the value of the voltage after the capacitor is charged to generate I-V characteristics of the photovoltaic array; and
determining the MPP of the photovoltaic array from the generated I-V characteristics. - View Dependent Claims (2, 3, 4, 5)
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6. A method of determining a maximum power point (MPP) of an energy source, the method comprising:
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determining current and voltage values associated with a capacitor under short circuit and open circuit conditions;
determining current and voltage values associated with the capacitor while a charging state of the capacitor is changing; and
using the determined current and voltage values to determine the MPP of the energy source. - View Dependent Claims (7, 8, 9, 10, 11)
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12. An article of manufacture usable with a photovoltaic array, comprising at least one photovoltaic cell, coupleable to a power inverter by way of a DC bus comprising a capacitor coupled across the DC bus and a switch positioned between the photovoltaic array and an AC bus of the inverter, the article of manufacture comprising:
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a machine-readable medium comprising instructions stored thereon to cause a processor to determine a maximum power point (MPP) associated with the photovoltaic array, by;
obtaining a maximum value of a current provided by the photovoltaic array substantially to the capacitor in response to a closing of the switch in a short circuit condition, the current charging the capacitor to progressively increase a voltage of the capacitor while the current decreases from the maximum value;
obtaining values of the current and the voltage while the capacitor is charging;
obtaining a value of the voltage in an open circuit condition after the capacitor is charged;
using at least some of the obtained values of the current and the voltage to generate I-V characteristics of the photovoltaic array; and
determining the MPP of the photovoltaic array from the generated I-V characteristics. - View Dependent Claims (13, 14, 15, 16)
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17. A system, comprising:
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a means for determining current and voltage values associated with a capacitor under short circuit and open circuit conditions;
a means for determining current and voltage values associated with the capacitor associated with a charging state of the capacitor; and
a means for using the determined current and voltage values to determine a maximum power point (MPP) of a photovoltaic source. - View Dependent Claims (18, 19, 20, 21, 22)
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23. A system, comprising:
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a photovoltaic array comprising at least one photovoltaic cell;
an inverter to invert DC power from the photovoltaic array into AC power;
a DC bus to couple the photovoltaic array to the inverter;
a capacitor coupled across the DC bus;
a current sensor coupled to the DC bus to determine current associated with the photovoltaic array;
a voltage sensor coupled to the DC bus to determine voltage associated with the photovoltaic array; and
a controller to determine a maximum power point (MPP) of the photovoltaic array based at least in part on current and voltage values respectively provided by the current sensor and the voltage sensor, the current and voltage values representing I-V characteristics of the photovoltaic array with the capacitor as a load. - View Dependent Claims (24, 25, 26, 27, 28, 29)
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30. An apparatus, comprising:
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a current sensor to determine current from a photovoltaic array, comprising at least one photovoltaic cell, during at least short circuit, open circuit, and capacitor-charging conditions;
a voltage sensor to determine voltage from the photovoltaic array during the open circuit and capacitor-charging conditions; and
a processor to determine a maximum power point (MPP) associated with the photovoltaic array by using the determined currents and voltages to directly determine I-V characteristics of the photovoltaic array and to use the I-V characteristics to identify the MPP. - View Dependent Claims (31, 32, 33, 34)
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Specification