Research On Wireless Electric Vehicle Charging Systems With High Misalignment And Load Variation Tolerance

wireless power transfer(WPT)technology has gained rapid development in recent two decades due to its advantages of plug-free,safe and convenient,environmentally insert and automatic control.It has become a new technology with great commercial potential applied to consumer electronics and industrial products.From low power implantable biomedical devices to electric vehicles and rail transits,wireless charging technology is indispensable.With the industrialization of electric vehicle wireless charging technology,there are still a series of bottleneck problems to be solved.In the research of compensation topology,there are some problems,such as unclear selection principle of topologies type,poor misalignment tolerance performance,and the system is vulnerable to the battery charging state variation,which hinders the popularization of wireless electric vehicle charging.Compensation topology is the core of wireless charging system,which plays a decisive role in the stable operation of the system.There are many kinds of compensation topologies,but there are few researches on wireless charging topologies for electric vehicles.This dissertation analyzes the common types of compensation topologies,summarizes the main characteristics of the wireless charging system compensation topology,and defines the characteristics of the topology suitable for electric vehicle wireless charging.According to the power,efficiency,voltage and current stress,frequency stability and other indicators,the double-sided LCC(DS-LCC)parameters are determined as the research object of this dissertation.The transfer efficiency of wireless charging system is closely related to the load.In this dissertation,the wide load adaptability of wireless charging system based on bilateral LCC compensation topology is studied.The constant current characteristic and the maximum equivalent load value of bilateral LCC topology are derived,and the necessity of its control is put forward.The synchronous rectifier is introduced to replace the DC-DC converter,which can effectively reduce the number of stages of the system.On this basis,a bilateral cooperative control method based on the primary side variable step perturbation and observation(VSP&O)method and the secondary side synchronous rectification control method is proposed,and its application range is proposed.The rationality and effectiveness of the proposed scheme are verified by experiments.When the control method in this dissertation is not used,the system efficiency changes with the load variation,and cannot always maintain the maximum efficiency.Instead,the dual control method in this dissertation is used After the simultaneous control method,the system efficiency can be kept at the maximum efficiency of 86 %.The output power of wireless charging system is closely related to the coupling.In this dissertation,the problem of limited power output caused by the change of coupling caused by the parking position of the existing LCC topology is studied.The feasibility of adjusting the primary side compensation inductor and compensation capacitor to regulate the output power of the system is analyzed in the DS-LCC topology,and the inductance and capacitance needed to be adjusted under weak coupling conditions are obtained.The working principle of adjustable inductor and capacitor is analyzed,which lays the foundation for adjusting output power control.In order to control the system effectively,a method of judging the coupling condition by using the primary side current is proposed,and the simulation of the whole system is carried out.After simulation,the system can achieve full power output under weak coupling and light load.The existing compensation topology is difficult to improve the misalignment and load variation tolerance.In this dissertation,a new hybrid topology is proposed to improve the performance of the system.Firstly,a new type of rectifier composed of two groups of uncontrolled rectifiers proposed in SAE J2954 is studied,which has the function of adjusting load.A hybrid topology based on SS topology and DS-LCC topology is proposed to improve the misalignment tolerance.Based on the above,the hardware circuit can be effectively used to improve the misalignment and load variation tolerance,and reduce the complex hardware detection circuits and real-time control.