Module-level DC/DC conversion for photovotaic systems : the delta-conversion concept

Photovoltaic (PV) systems are increasingly used to generate electrical energy from solar irradiation incident on PV modules. PV modules are formed by placing many PV cells in series. The PV system is then formed by placing a number of PV modules in series in a string. In practical cases, differences will exist between output powers of the PV cells in the various PV modules, e.g., due to (part of) the modules being temporarily shaded or pollution on one or more PV cells. Due to the current-source-type behavior of PV cells and their series connection, these differences will lead to a relatively large drop in PV-system output power. This paper addresses this problem by adding dc/dc converters on PV-module level. The so-called delta-conversion concept is introduced that aims at averaging out differences in output power between groups of PV cells within modules and between modules inside the PV system. All groups of PV cells can then output their maximum available power, such that a drop in output power of the total system is prevented. This paper describes implementation details, compares the delta-conversion concept with other state-of-the-art module-level power-conversion concepts, and presents first measurement results obtained with a demonstrator system.