Step-charging technique for CC/CV mode battery charging with low-cost control components in IPT systems

Abstract

In wireless power transfer technology, power control technique is required to realise constant current (CC) and constant voltage (CV) modes for battery charging. CC and CV modes are needed to effectively charge lithium (Li)-ion batteries to ensure long life span and maximum capacity utilisation. The use of additional battery charging circuitry reduces efficiency, increases volume, and increases circuit complexity. The frequency modulation method is a method that can control power without an additional charging circuit, but a high-resolution controller is needed to control the voltage and current for charging the battery by frequency modulation. This study proposes a system that controls current and voltage for CC and CV modes through a step-charging method using a battery hysteresis with a low-cost control system. The in-band communication circuit is analysed and used to link the primary and secondary sides of the inductive power transfer (IPT) coils, which enables effective feedback control without an additional wireless communication module. This method enables high-efficiency charging while minimising the overall size and cost of mobile IPT applications such as power tools. The proposed system shows 90.3% transfer efficiency with a 20.75V, 4Ah Li-ion battery at 7mm distance.