Research On Secondary Side Control Technology Of Magnetic Coupling Resonant Wireless Charging System

In recent years,the number of electric vehic les has increased remarkably with the encouragement of government policy and market demand.However,the development of electric vehicles is limited by the problem that charging infrastructure is difficult in operability,large in area and poor in security.Wireless charging technology,which is based on wireless power transfer theory,realizes contactless charging to electric vehicles by inductive coupling or magnetic coupling resonance.It has broad application prospect with advantages of good sealing performance and good security.To meet the requirement of application,it need further research and improvement in overall efficiency,transmission distance,misalignment tolerance and control stability.This paper mainly focuses on secondary side control technology of magnetic coupling resonant wireless charging system.A prototype of the wireless charging system is designed,each part of the wireless charging system is analyzed and optimized based on wireless power transfer theory.Firstly,this paper starts with resonant topology of wireless charging system,demonstrates the rationality of using S-S resonant topology.The characteristic of S-S resonant topology is solved by mutual inductance coupling model and circuit equations,and then the parameter design method is obtained to improve the efficiency of the resonant topology.The effect of parameter changing of resonant component to the resonant characteristic in reality is analyzed to get the precision requirement of the resonant topology.Secondly,a solenoid type magnetic coupler is designed.Based on magnetic circuit theory and mutual inductance theory,the relationship between coupling coefficient and winding design is analyzed.Loose wind ing design is proposed to improve the coupling coefficient and smooth the magnetic flux in the core.The core structure is optimized to reduce the usage of ferrite core with little coupling ability loss.Thirdly,the simplified charging circuit in secondary side based on semi-bridgeless active.The analys is and modeling of semi-bridgeless active rectifier is completed by small-signal modeling method.The control loop is analyzed based on Bode plot of the open-loop system,the compensation element is designed accordingly and the PWM controller is designed based on FPGA.The designed control loop is simulated by PLECS.The problem of control stability caused by resonant topology is analyzed and solved.Finally,the wireless charging system experimental platform is completed with existing inverter source and designed resonant topology,magnetic coupler,and charging circuit.The experimental results show that the total effic iency of designed parts is 84.5% in conditions of 15 cm transmission distance,24 V battery voltage and 5A charging current.The system has a certain misalignment tolerance with a relatively high efficiency.In charging control experiment,the system can fully response the control in 3ms with no overshoot and oscillation.