Medium voltage AC collection grid for large scale photovoltaic plants based on medium frequency transformers

A three phase medium voltage (MV)/medium frequency (MF) power collection grid for megawatt (MW) scale photovoltaic plant (PV) is proposed. The proposed ac collection grid is shown to increase power density and improves system modularity while maintaining high efficiency levels. The PV panels power standard three phase PWM voltage source inverters (VSI) to generate MF ac voltage. Various VSI outputs are combined in series via MF transformers to form the proposed MF ac collection grid. A three phase ac-ac cycloconverter interfaces the MF grid with the 60Hz mains. An 80MW PV power plant located in Eggebek/Germany is used for comparison in the design example. Detailed simulation and calculations of the proposed system demonstrates size/weight reduction and overall efficiency improvement of 2%.