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

Module-level DC/DC conversion for photovoltaic systems

Photovoltaic (PV) systems are increasingly used to generate electrical energy from solar irradiance incident on PV modules. Each PV module is formed by placing a large amount of PV cells, typically 60, in series. The PV system is then formed by placing a number, typically 10–12, of PV modules in series in a string and sometimes by placing multiple strings of series-connected PV modules in parallel, depending on the desired output voltage and power range. In practical cases, differences will exist between output powers of the cells in the various PV modules, e.g. due to (part of) the modules being temporarily shaded, pollution on one or more PV cells, or even spread in cell behaviour. Due to the current-source-type behaviour 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 concept, named ‘delta conversion’, aims at averaging out differences in output power between groups of PV cells within modules and between modules inside the PV system. As a result, all these groups of PV cells can output their maximum available power, such that a drop in output power of the total system is prevented. This paper 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

A driver IC for photovotaic module-integrated DC/Dc converters

Photovoltaic (PV) installations suffer from a disproportional decrease in output power in case irradiance differences are present in the system. The Delta converter improves the output power in such cases by routing current differences around the shaded substring or module. This paper presents a driver IC for the Delta converter that simultaneously reduces its cost and improves its reliability. The driver IC integrates the complete control loop, power supplies, protections and references. The driver IC demonstrated trouble-free operation for 3 months under real-life conditions in a PV installation with different shading patterns. Depending on the shading pattern the Delta converter energy gain was 8%-18%