Passivity-based control for a high reduction ratio step-down converter in a battery charger application

This paper presents a control strategy for a high reduction ratio DC-DC step-down converter used in battery charging applications. The studied converter is conformed by a conventional step-down converter that has been modified with a capacitive active switching cell inserted at the input. This topology allows a high reduction ratio in contrast to traditional step-down converters. The battery charging strategy employed in this work is the well-known constant current and constant voltage. The design of the proposed control scheme results in two control loops, known as inner and outer control loops, which are aimed at guaranteeing that the battery charging profile is followed. Passivity-based control techniques are used to design the inner control loop. This loop is aimed at constant current injection which acts during the constant current and voltage stages. The voltage regulation is designed as a PI controller which is aimed to ensure the voltage regulation to a desired reference. The outer control loop acts only during the constant battery voltage stage. Finally, numerical simulations are carried out to assess the performance of the proposed control strategy used in a battery energy storage system application.