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Module-Level Power Converters For Parallel Connected Photovoltaic Arrays
MISSOURI UNIV OF SCIENCE AND TECHNOLOGY ROLLA
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The number of installation locations with unshaded southern exposure over an area large enough for a conventional photovoltaic PV array is limited. If the array s performance under parital shading could be increased, the number of suitable installation sites would increase significantly. A typical solar panel generates up to 200 W at about 26 V. A typical inverter is rated for at least 250 V on its input terminals. Conventionally, PV panels are connected in series strings that achieve the desired system voltage, and then these strings are connected in parallel to achieve the desired system power rating. Unfortunately, if one panel is compromised due to shading, obstructions, damage, etc. the output power of its whole string is significantly reduced. Since PV system designers and installers are aware of the detrimental effects of shading, they design for as minimal shading as possible. With the proposed approach, panels can be connected in parallel instead. Then any single compromised panel will only affect that particular panel, rather than the whole array. This will cause the average system output power to increase. While shading should still be avoided or minimized, moderate shading can be tolerated, so more installation sites can be considered. In the proposed array topology, each individual PV panel has an integrated dc-dc converter which increases the input voltage by a fixed gain. The output of the converter could then be directly connected to a grid-tie inverter that performs maximum power point tracking MPPT. Good source and load regulation are needed so that individual panels operate near the same voltage, regardless of system voltage and individual panel power production.
APPROVED FOR PUBLIC RELEASE