Direct Connection of Supercapacitors to Photovoltaic Panels With On–Off Maximum Power Point Tracking

A system dedicated to energy storage is presented. It allows energy storage from photovoltaic panels to a compressed air accumulator. This accumulator is controlled to enable compression and expansion modes under Maximum Efficiency Point Tracking (MEPT). A Maximum Power Point Tracking (MPPT) power converter is as usual connected to the solar cells. An intermediary storage tank consisting of supercapacitors and its associated power converter are inserted as a buffer. They adapt the power extracted from the solar cells under the MPPT condition to the power injected into the hydro-pneumatic system under the MEPT condition. Energy transfer from the solar cells to the hydro-pneumatic system is sequentially operated. The number of cascaded power converters decreases the global efficiency of this hybrid accumulator. This paper introduces a solution that consists of the reduction of the number of power converters. It is obtained by a direct connection of the supercapacitors on the solar panels to lower losses. Taking advantage of the sequential energy transfer, the MPPT mode is kept for the solar panels, as well as the MEPT mode for the hydro-pneumatic accumulator. The general topologies, sizing criteria, and control are presented, as well as considerations on efficiency.