Advanced digital current prediction for current ripple reduction in DC-DC converters for photovoltaic applications

Photovoltaic applications require very small current and voltage ripples at the output of the solar cells to avoid power losses due to deviations from the maximum power point. Digital control offers optimization potentials to reduce this ripple without increasing the requirements on the analog-to-digital converters or the loop delay. This paper investigates the achievable current ripple reduction for two different digital current prediction algorithms applied to a hysteretic controlled photovoltaic submodule converter. A basic method relying on the continuity of the inductor current and an advanced algorithm, which compensates loop delay have been implemented in VHDL. Both methods are compared in structure and simulation results. The basic current prediction reduces the current ripple by 11 %, whereas the advanced current prediction decreases the ripple in total by 26 %. The whole controller including the advanced current prediction requires less than 0.1mm² in a 150nm CMOS technology.