Design of cascaded control loop for solar power optimizer based on a buck-boost converter

Abstract

Power optimizers are dc-dc converters, featuring maximum power point (MPP) tracking operation, deployed on a per module basis in modern PV plants, adding value on flexibility, diagnostic capability and energy yield. This paper considers the non-inverting buck-boost converter used as a power optimizer, with emphasis on the control scheme applied to it. In the analysed configuration, the converter inductor current and PV voltage are controlled in a cascaded fashion, where the outer loop controlling the PV voltage provides the inductor current reference for the fast inner loop. With the selected control technique, the transfer functions describing the plant exhibit a first order like behaviour, hence facilitating the controller design, allowing to avoid using lead-lag networks or controllers whose tuning is non-trivial. The controlled converter performance in tracking the MPP voltage is analysed by means of simulations after a simple proportional integral (PI) controller is added in the voltage loop and another PI controller is adopted in the current loop.