Inverter control methodology for distributed generation sources connected to a utility grid
First Claim
1. A method for maximum power point tracking (MPPT) in a distributed generation system coupled to an alternating current (AC) power grid, comprising:
- comparing a current gain of the distributed generation system between zero crossings of the AC power grid;
if the current gain has decreased in the current gain comparing step, comparing a change in power magnitude of the distributed generation system between the zero crossings of the AC power grid with an expected power decrement and, if the change in power magnitude is greater than a factor q of the expected power decrement, incrementing the current gain, otherwise decrementing the current gain;
if the current gain has not decreased in the current gain comparing step, comparing the change in power magnitude of the distributed generation system between the zero crossings of the AC power grid with an expected power increment and, if the change in power magnitude is less than the factor q of the expected power increment, decrementing the current gain, otherwise comparing the change in power magnitude to a power incline function and incrementing or decrementing the current gain based on the comparison.
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Abstract
The present invention provides an improved control methodology for maximum power point tracking (MPPT), anti-islanding, and output current regulation for distributed generation sources connected to a utility grid. The control includes enhancements for MPPT and regulating the inverter output-current that is sourced into the utility grid. In addition, the functions associated with MPPT, anti-islanding detection and output current regulation are integrated together; the MPPT algorithm operates in conjunction with the anti-islanding detection, and the output current regulation operates in conjunction with the MPPT algorithm.
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Citations
37 Claims
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1. A method for maximum power point tracking (MPPT) in a distributed generation system coupled to an alternating current (AC) power grid, comprising:
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comparing a current gain of the distributed generation system between zero crossings of the AC power grid;
if the current gain has decreased in the current gain comparing step, comparing a change in power magnitude of the distributed generation system between the zero crossings of the AC power grid with an expected power decrement and, if the change in power magnitude is greater than a factor q of the expected power decrement, incrementing the current gain, otherwise decrementing the current gain;
if the current gain has not decreased in the current gain comparing step, comparing the change in power magnitude of the distributed generation system between the zero crossings of the AC power grid with an expected power increment and, if the change in power magnitude is less than the factor q of the expected power increment, decrementing the current gain, otherwise comparing the change in power magnitude to a power incline function and incrementing or decrementing the current gain based on the comparison. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A system for improving regulation of an output current of an inverter coupled between a distributed generation system and an alternating current (AC) power grid, comprising:
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a proportional-integral-derivative (PID) controller;
a feed forward controller; and
a power normalization controller. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23)
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24. A method for maximum power point tracking (MPPT) in an inverter coupled between a distributed generation system and an alternating current (AC) power grid, comprising:
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enhancing a quality of an output current of the inverter through combined use of a proportional-integral-derivative (PID) controller, a feed forward controller, and a power normalization controller; and
performing the MPPT on the enhanced quality output current to improve stability of the MPPT. - View Dependent Claims (25, 26, 27, 28, 29)
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30. A method for detecting an islanding condition in a system including a distributed generation system and an inverter coupled between the distributed generation system and an AC power grid, comprising:
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comparing an RMS voltage of the AC power grid with an island threshold;
if the RMS voltage is greater than the island threshold, determining if a change in the RMS voltage reflects a change made to a current gain of the inverter when islanding;
if the change in the RMS voltage reflects a change made to the current gain of the inverter when islanding, then incrementing a number of island hits;
processing the number of island hits that occurred during a collection period; and
enabling or disabling the inverter based on the number of island hits that occurred during the collection period. - View Dependent Claims (31, 32, 33, 34, 35, 36)
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37. A method for detecting an islanding condition in a system including a distributed generation system, an inverter coupled between the distributed generation system and an AC power grid, and a maximum power point tracking (MPPT) system for tracking a maximum power point (MPP) of the distributed generation system, comprising:
using a change in current gain determined by the MPPT system to detect an islanding condition.
Specification