Inductive Power Transfer With High Order Constant Current And Optimization Of Misalignment Tolerance

Wireless power transfer(WPT)technology is a new frontier technology in the field of electrical engineering,which utilizes soft media(air,water,etc.)to transfer power energy to the load through electromagnetic conversion.The magnetic coupling wireless power transfer technology can realize the power transmission in medium distance,which is suitable for most occasions,and has been paid close attention by the industry and the academia.However,there are still some problems in wireless power transfer technology,such as imperfect model construction,low energy transmission efficiency,poor anti-misalignment performance and high system cost,which hinder the practical process of the technology and is urgent to break through.In this thesis,the modeling of magnetic coupling resonant power transfer system,the design method and application of high order topology,the power transmission characteristics of the new topologies and the improvement of misalignment tolerance are studied with theories and experiments.This thesis supported by the sub project "wireless charging system interoperability testing and safety evaluation technology(2018YFB0106304)" of the national key R & D project "key technology of high performance charging system based on new power electronic devices" and its supporting science and technology project of State Grid Corporation of China(52110418003G).The main research work is as follows:Firstly,the modeling and transmission characteristics of basic compensation network are studied.Aiming at the problem of high order of the traditional generalized state space averaging(GSSA)model and the complexity of modeling,a discrete-time modeling method for SS compensation wireless power transfer system is proposed.According to the different switching states of the converter,the discrete-time model of WPT is designed,and the control to output transfer function in z-domain is obtained,which can accurately and quickly describe the complete dynamic process of the state variables of the WPT system,while the system order does not increase.On this basis,a digital controller considering the control delay of primary and secondary sides is designed to meet the performance indexes of phase margin,amplitude margin,stability time and overshoot.Secondly,the basic configuration of high order compensation circuit is analyzed.A wireless charging system based on hybrid topology is proposed to meet the demand of constant current and constant voltage sectional charging.The output characteristics and resonant conditions of high-order basic unit circuit are analyzed.Based on T-type circuit,the parametric characteristics of three degrees of freedom in double LCC(DLCC)resonant network are studied.The circuit structure and parameters design method of LCC type compensation network structure for constant current output and constant voltage output in wireless charging system are obtained.Considering the output stability of the circuit switching,an additional capacitor and switch are added to the secondary circuit to realize the switching charging of the battery with constant current and constant voltage,which eliminates communication and complex control.In the constant current mode,the input impedance is pure resistance,and there is almost no reactive power input.In the constant voltage mode,the input impedance is inductive,which can realize zero voltage switching of the inverter.According to the proposed parameter design method,a power transmission prototype is designed,and the effectiveness of the proposed method is verified.Then,in view of the problems of input impedance capacitance and discontinuous conduction mode of rectifier in the traditional DLCC compensation network under large load,two compensation topologies,LCC-S and LCC-SP,are proposed for current mode load,whose output current is independent of the load.In the two new constant current topologies,the device stress is more balanced,the input impedance is always in the inductive range,and the rectifier works in continuous conduction mode,which ensures the high efficiency of the whole system.ZVS soft switching can be realized.When the load is large,the impedance angle is close to zero,the circuit debugging is simple,the design freedom is high,and the output power is not limited by magnetic coupling mechanism.The correctness of the theoretical analysis is verified by the experimental platform.Finally,because the magnetic coupling mechanism of the wireless power transfer system is two non-contact coils,the occurrence of misalignment often exists,the output fluctuation with coupling is very obvious,and the improvement ability through control strategy is limited.In order to overcome the robustness problem of wireless power transfer system with variable coupling,a misalignment performance improvement method based on optimal design of compensation parameters is proposed in this paper.This paper studies the characteristics of constant current type LCC-S system with detuning parameters.On the one hand,it solves the problem of sudden increase of inverter current under offset,on the other hand,it enhances the robustness of the system to misalignment and load changes.For the proposed LCC-SP compensation network,the relationship between the misalignment tolerance and the range of optional parameters is clarified.This method can not only ensure the rated output of the central coupling coefficient,but also extend the anti-misalignment range of both coupling coefficient changing directions.The proposed parameter optimization design method ensures that the system has excellent anti-misalignment ability and maintains high efficiency.