Research On High Frequency Wireless Power Transfer System With Multiple Receivers Based On Magnetic Coupling Resonance

Wireless power transfer(WPT)technology is widely accepted and applied in the market due to its safety and convenience,which achieves isolation charging between terminals and power supplies with non-contacting manner.In order to achieve a larger charging area and a longer charging distance with a smaller volume,WPT technology for small-sized smart terminals is gradually oriented to high frequency.However,the transfer efficiency and unstable output will be induced due to the unmatched impedance of load network from driver sources,increase of high-frequency loss of coupling coil,quality factor deduction and power distribution problems towards multiple receivers.For all these problems mentioned above,this paper studies the system power allocation strategies according to the system modeling,load network impedance matching and practical requirements based on 6.78 MHz multi-receiver WPT system.The main research contents are listed as follows:Firstly,since high frequency class E power amplifier cannot operate efficiently in a wide load range,this paper proposes an improved load network configuration method.By reasonably configuring the input characteristic impedance and quality factor of load network,the load bandwidth can be greatly improved.The improved class E power amplifier not only has the advantages of high frequency efficiency of the traditional class E power amplifier,but also has wide load adaptability,which improves the reliability and practicability of the driving source.Secondly,aiming at the small size of smart terminal and the influence of distribution parameters on quality factor,a basket-type coil with turn-to-turn crossing angle is proposed.Based on the researches of conventional single-layer planar spiral coils,the overall electrical performance of the novel coil structure is analyzed,including the equivalent lumped parameters and distribution parameters.Furthermore,the improvement of the system performance by the new struct ure is discussed.In order to improve the misalignment tolerance of small terminal wireless charging,a method to make the magnetic field of high frequency coil uniformly distributed is proposed.Then,a PCB coil with uniform distribution of magnetic field is designed.Thirdly,in order to solve the problem of uneven power distribution and inability of load operation caused by different load power levels and relative positions of multiple receivers,an output power stabilization control strategy based on perturbation and observation(P&O)algorithm is proposed.With the power requirements of each receiver and multi-objective optimization algorithm,the total power of the system is centralized and the efficiency is improved.The expression of power distribution ratio and primary/secondary current is derived.Then the load impedance regulation range is obtained according to the expression.The impedance matching parameters under the condition of load power are obtained by analyzing the expression of variable load impedance transformation.After that,the effectiveness of power allocation is guaranteed.Finally,a multi-receiver experimental platform for high-frequency and low-power applications is set up.The relationship between mutual inductance and magnetic field distribution is analyzed to verify the proposed power allocation strategy.The efficiency tracking process under fixed output power and the effectiveness of the proposed P&O algorithm are verified.With a wide range of coupling coefficient and controllable load impedance,the system achieves stable output power and higher system efficiency.