Research On Three-Coil Wireless Battery Charger For Self-Adapting Battery Charging Profile

Inductive power transfer(IPT)technology has been widely used in the portable equipment.Since lithium-ion batteries are mostly used as energy storage devices,the wireless battery charger should efficiently provide an initial constant current(CC)and a subsequent constant voltage(CV)output for the battery.At present,the existing schemes mainly include two-stage converter,hybrid topology,or high-order network,etc.,resulting in large number of circuit components,complicated control,low efficiency and poor reliability.To solve the above problems,the three-coil IPT system with S-S-S compensation topology can automatically realize CC-to-CV transition by adding an assistive coil and a passive rectifier bridge on the primary side.In both charging modes,it can ensure near zero reactive power circulation in the circuit and soft switching,which can reduce device stress and improve transmission efficiency.However,the output gain of the simple S-S-S compensation network is limited by the parameters of the magnetic coupling mechanism,mainking it difficult to meet the requirements of different battery charging profile.Therefore,this dessertation aims to improve the existing three-coil IPT system based on the S-S-S compensation topology.Retaining the function of automatic CC-to-CV transition in the three-coil topology,the assistive side and secondary side compensation topologies are improved to avoid the limitation of the coupling mechanism parameters to the output gain,so that it could adapt to different battery charging curves.In this dessertation,a specific compensation network is firstly constructed by the resonant cavity method to provide a voltage source with adjustable amplitude for the auxiliary circuit.Accordingly,an improved three-coil battery wireless charger that can self-adapt battery charging profile is proposed.In the proposed topology,a specified compensation network connected into the assistive coil is adopted to make the output voltage threshold not subject to the magnetic coupling mechanism parameter and self-adapt any battery charging profile.Then,according to the equivalent transformation characteristics of the three-coil topological input power supply,the LC compensation topology is introduced in the secondary side by the network matrix analysis.Compared with S-type compensation,LC-type compensation only adds one controllable parameter,which effectively decouples the output gain from the magnetic coupling mechanism.It should be emphasized that both improvements retain the automatic CC-to-CV transition of the three-coil IPT system without additional control and with the function of automatic open-circuit protection.Finally,to verify the proposed three-coil IPT systems for self-adapting battery charging profile,two experimental prototypes are built to verify the effectiveness of the improvement on the auxiliary side and the secondary side.