An IPT battery charger with near unity power factor and load-independent constant output combating design constraints of input voltage and transformer parameters

Abstract

Inductive power transfer (IPT) techniques are becoming popular in battery charging applications due to some unique advantages compared to the conventional plug-in systems. A high-performance IPT charger should provide the battery with an efficient charging profile consisting of constant charging current and constant charging voltage. However, with a wide load range, it is hard to realize the initial load-independent constant current (CC) and the subsequent load-independent constant voltage (CV) using a single IPT converter while maintaining nearly unity power factor and soft switching of power switches simultaneously. This paper systematically analyzed the characteristics of an LCC-LCC compensated IPT converter and proposed a design method to realize the required load-independent CC and CV outputs at two zero-phase angle frequencies. The design also combats the constraints of an IPT transformer and input voltage, thus facilitating the use of a simple duty cycle control operating at two fixed frequencies for both CC and CV operations. The design criteria, control logic, and sensitivities of compensation parameters to the input impedance and load-independent output are discussed. Finally, an IPT battery charger prototype with 1 A charging current and 24 V battery voltage is built to verify the analysis.