Design Of Magnetic Coupling Wireless Power Transmission System With Constant Current And Constant Voltage Output Characteristics

Wireless power transmission(WPT)is a new technology,which can wirelessly transmit power from the primary side to the secondary side without physical contact.It is considered as a new choice of power transmission system in the future.When charging the battery,it is necessary to use the mixed mode of constant current(CC)/constant voltage(CV)to ensure the long life and maximum capacity utilization of the battery.Therefore,it is of great significance to study WPT system with CC/CV characteristics.This paper designs a more controllable magnetic coupling resonant wireless power transmission(MCR-WPT)system which is suitable for charging lithium battery in CC/CV mixed mode.The system realizes CC/CV output through matching circuit.Specifically,LCL-P is used to realize constant current output and LCL-S is used to realize constant voltage output,and this paper theoretically proves that the two topologies have constant current or constant voltage characteristics respectively.The advantage of this system is that it doesn’t need to add additional wireless data communication links or switch multiple frequencies to set CC/CV mode.The receiving circuit is used to realize battery charging without extra battery management circuit,and the circuit topology of WPT is switched independently according to the battery state,without extra DC-DC circuit or active rectifier bridge to maintain CC/CV mode,thus reducing the hardware complexity and software control complexity of the circuit and further improving the overall efficiency of the system.In addition,this paper solves the power and efficiency expressions for LCL-P topology and LCL-S topology respectively,and briefly analyzes the characteristics of the two different topologies by establishing three-dimensional coordinate diagrams.In order to improve the total power of power transmission,the closed-loop PI algorithm is used in the primary side to maximize the current in the primary coil,which reduces the system error caused by devices in practical application and improves the stability and efficiency of the system in CC/CV mode.The feasibility of the proposed scheme is verified by mathematical theory analysis,software simulation and experiments.Finally,it is verified by software simulation and physical experiments that the WPT system has the output characteristics of CC/CV mode.The oscillograph waveform analysis of each module of the system and the waveform diagram of the load voltage and current when the system works in CC/CV mode are given.The experimental results show that when the load resistance changes from 5Ω to 20Ω,the load current changes less than 3% in CC mode and the load voltage changes less than 5% in CV mode.This scheme is suitable for low-cost and high-efficiency small and medium-power MCRWPT charging system.