Realization of a New Inverter Circuit for Direct Photovoltaic Energy Feedback into the Public Grid

Abstract
A new regulated utility interactive inverter for direct photovoltaic energy feedback to the mains has been realized. A modulated buck converter converts the photovoltaic dc current to a rectified 50-Hz sine wave current, and the following self-commutated half-bridge generates a 50-Hz sine wave current, which is fed into one phase of the public power grid. This nonclassical inverter needs only three power transistor switches and isolates the grid and the photovoltaic array using a commercial 50-Hz transformer. It acts as a current source, and due to pulsewidth modulation its output is a sine wave current with very low total harmonic distortion of one percent. The overall efficiency of the 1-kW prototype is at least 88 percent between 250 and 1000 W, and the projected efficiency is over 90 percent for 1-20 kW. Furthermore, a circuit which tracks the maximum power available from the photovoltaic generator has been developed. This circuit regulates the input power to its maximum by detecting the phase angle between the voltage and power ripples at the inverter input.

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