Study On Constant Output Voltage In Multi-Coil And Multi-Load Wireless Power Transfer System

Wireless power transfer technology has a wide range of potential application value in daily household and office areas where there are a large number of low-power terminal devices,and most of the devices are powered by constant voltage.However,the existing multi-coil multi-load WPT system is difficult to take into account both the large power supply range and the constant voltage output design,and little literature analyzes the influence of cross couplings between the coils on the load voltage.So this thesis focuses on the multi-load constant voltage design with consideration of cross couplings and provides a feasible constant voltage wireless power supply scheme for multi-load where low-power terminal equipment is ubiquitous.The multi-load WPT system studied in this thesis is an improvement and combination of the existing multi-load WPT structure.It consists of multiple one-to-one WPT subsystems in cascade(serial)and parallel structure.And the cascaded one-to-one structure facilitates the expansion of the load power supply range,and provides an approximately constant voltage AC bus for the parallel structure at the same time;the parallel one-to-one structure takes power from the AC bus,and facilitates the constant load voltage design at the same time.Based on this system architecture,three progressive multi-load constant voltage wireless power supply schemes are considered when considering cross coupling of coils.(1)The constant voltage design of a multi-coil multi-load WPT system based on passive compensation.Firstly,design the passive compensation network for constant voltage of every WPT subsystem respectively.Secondly,analyze the effect of cross couplings between coils on the load voltage and the phase angle of input voltage and current with different compensation structures.Thirdly,a suitable passive compensation structure can be selected based on the cross coupling or the design objective to emphasize the constant voltage effect or the system efficiency.Finally,do some simulation verifications about the influence of cross coupling on load voltage and phase angle of input voltage and current in cascaded and parallel structure respectively.(2)The constant voltage design of a multi-coil multi-load WPT system based on the magnetic field decoupling method.Based on the passive compensation method,the shielding sheets are added to decouple the cross magnetic field,and the cross coupling is reduced so to its influence on the constant output voltage.Firstly,the accuracy of finite element simulation in magnetic field parameter measurement is discussed.Then design the shielding scheme of the four-coil structure,which is the smallest basic unit in the cascade structure and the parallel structure using COMSOL finite element simulation.Finally,make the two-load constant-voltage experimental verification of the Ferrite-Aluminum-Ferrite sandwich shielding scheme in cascade structure and the unshielded scheme in the parallel structure,and the results show the feasibility of the proposed magnetic field decoupling method.(3)The constant voltage design of a multi-coil multi-load WPT system based on the hybrid method.High voltage regulation accuracy cannot be achieved under cross-coupling and load disturbance conditions using whether single passive compensation method or magnetic field decoupling methods.Therefore,based on passive compensation and magnetic field decoupling methods,an active closed-loop feedback regulation circuit is added at the load side to perform feedback regulation of the load voltage so as to achieve higher regulation accuracy and anti-interference performance.In the proposed hybrid method,the passive compensation method and the magnetic field decoupling method provide approximately constant input voltage for the active closed-loop circuit,which solves the auxiliary power supply of the active circuit at receiving side innovatively.So that the circuit can get rid of the wired connection used in the existing literature and maintain the essential feature of "wireless" in the WPT system.Finally,a three-load WPT system experimental platform based on the proposed hybrid method with cascading and parallel structures was built to verify the feasibility of the proposed hybrid method.The proposed three types of multi-coil and multi-load WPT system constant voltage output design schemes in this thesis have different applications,and they can be selected based on cross-coupling condition,voltage regulation accuracy requirement,space location condition,and efficiency-focused condition in actual situations.All schemes can provide theoretical references for practical application of the project.