High-Gain Step-Down DC–DC Converter Employed in a Battery Charging Application

Abstract

In this paper, a model-based control scheme for a DC-DC power converter as a battery charger is presented. The proposed DC-DC converter for this task is a high-gain step-down converter based on the switched inductor concept. Thus, the considered topology is able to highly reduced the output voltage on a single stage compared to traditional step-down converters. The proposed control strategy is aimed at fulfilling the requirements of the constant current and constant voltage algorithm widely used for battery charging purposes. Given the structure of the system model, the proposed control scheme results in a multi-loop controller, which is structured by a PI current control loop and a PI voltage control loop. During the constant current stage, the system is required to inject constant current into the battery while the voltage freely increases. Thus, the current control loop maintains the input battery current at a constant reference value. On the other hand, in the constant voltage stage, the battery is regulated to a desired constant value. Hence, in the end, both control loops act on the system to fulfill the objective. An external battery management system is aimed at controlling the transition between both modes, considering the physical thresholds of current and voltage required by the battery to guarantee the successful charging process. Finally, the performance of the proposed control strategy for battery charging is assessed on an experimental setup.

Keywords

• Battery charger
• constant current and constant voltage
• DC–DC converters
• model-based control