Research On Anti-misalignment Technology And Optimal Design For Wireless Power Transfer Systems

Wireless Power Transfer(WPT)technology has gained great attention of worldwide researchers because of its environmental adaptability,safety,convenience,simplicity and other advantages.At present,WPT technology has successfully applied in percutaneous medical equipment,underwater electrical equipment,various consumer electronics,rail transit vehicles and electric vehicles.In many WPT applications misalignment of coupler is ineluctable,which reduces the coupling coefficient and mutual inductance between the primary and secondary coil,and decreases the stability of the output power,hindering the further popularization and implementation of WPT technology.Therefore,it is necessary to study anti-misalignment method in order to improve the output stability of WPT system with coil misalignment.Generally,there are three ways to improve the misalignment performance of the WPT system.Radically,the first way is to optimize the overall structure of the coupler for the purpose of creating a magnetic field environment in which the flux changes little within the misalignment range and postponing the decreasing trend of mutual inductance,so as to improve the output stability of the system.Secondly,it is feasible to optimize the circuit topology according to the change of mutual inductance when the coupler is misaligned,so that the output power of the system can remain stable when the mutual inductance changes.Finally,when the coupler and circuit topology are both determined,optimizing the circuit parameter to reduce the sensitivity of output performance with various mutual inductance is also an important way to improve the anti-misalignment ability of the system.The output characteristics of WPT system in misalignment case are analyzed by combining the misaligned characteristics of coupler with the output characteristics of WPT system.Then,based on the above three approaches,anti-misalignment methods are proposed for series-series(SS)compensated topology and LCL topology WPT system respectively:1)Anti-misalignment method of WPT system based on SS compensated topology.Firstly,by analyzing the output characteristics of the system when the coupler is misaligned in tuned and detuned states,the compensated capacitors is selected as the optimized parameter to improve the anti-misalignment ability of the system from the consideration of parameter optimization.Then,the enumeration method is used to find the optimal compensated capacitors,which maximizes the allowable range of mutual inductance when the fluctuation ratio of voltage gain and the range of load value are set.At the same time,the optimal compensated capacitors is required to satisfy the zero voltage switching characteristic of the system.Finally,an experimental prototype is built to compare the output fluctuation of the tuned and optimized WPT system,and to validate the proposed method.2)Optimizing the LCL based WPT system and its anti-misalignment method.Firstly,a dual coupled LCL based WPT system was proposed in this paper by replacing the resonant inductor with a pair of coupled coils in the traditional LCL compensation network,and the DDQ coil is selected as the coupler optimally,can realize dual-channel power transfer.Through theoretical comparison,it is concluded that the transmission efficiency and output stability of the system are better than those of the traditional single-coupled LCL topology WPT system.Then,based on the principle of optimizing the circuit topology,an anti-misalignment method of topology switching is proposed to further improve the output stability of the WPT system.Finally,the proposed system and its anti-migration method are verified by experiments.