<p>This paper presents a control strategy of secondary-side buck converter in the series–parallel topology-based wireless charging systems, to realize a robust constant current/voltage charging. In the series–parallel topology-based wireless charging systems, the relationships between the duty ratio of driving signal of the secondary side buck converter and the charging current and charging voltage are derived. And in the processes of constant current charging and constant voltage charging, the behaviors of the duty ratio, according to the change of battery internal resistance value are investigated. Based on that, a control strategy is presented to realize a robust constant current/voltage charging. A prototype of battery charging system, which materialized this strategy, is constructed and the presented strategy is validated by some experimental results.</p>