A maximum power point tracker variable-dc-link three-phase inverter for grid-connected PV panels

This paper introduces a variable dc-link control scheme of a grid-connected three-phase inverter for photovoltaic power plants with maximum power point tracking capability. The control scheme includes two layers. An inner current control loop injects power with an adjustable power factor into the ac grid. An outer control loop introduces small changes in the dc-link voltage based on a modified version of the well known incremental conductance algorithm in order to track the point of maximum power in the photovoltaic array. A chief advantage of the proposed scheme is the elimination of the intermediate dc/dc converter stage usually included to realize the maximum power point tracking function. The control scheme is validated in a 425kW system using real irradiance data provided by the U.S. Department of Energy´s National Renewable Energy Laboratory through a detailed computer simulation in the PSCAD/EMTDC mathematical software package.