Design And Experimental Research Of Wireless Charging System Based On Magnetic Coupling Resonance Technology

Wireless charging technology is also known as wireless power transmission technology.The charging system designed based on wireless power transmission technology is equivalent to a transmission path of electric energy,and it transfers electric power at the entrance of the passage towards the electrical load located at the exit of the passage.Due to the convenience of its application,wireless power transmission-related technologies have been a hot topic in both domestic and foreign research in recent years.The wireless power transmission based on magnetic coupling resonance system designed in this project,aims to realize a wireless power transmission application with high efficiency to allow for transmission distance across 100 mm or more,and transmitted power of more than 100 W,on condition of low operating frequency(fixed frequency)and implementation with load of small resistance.This paper compares the characteristics of five kinds of wireless charging mode,describes the advantages and prospects of mode of electromagnetic coupling resonance wireless power transmission,and summarizes the recent research status in both domestic and foreign countries.The theoretical analysis for wireless power transmission based on magnetic coupling resonance circuit system model has been done through the equivalent circuit approach,and gives mathematical deduction telling that there are different M value between conditions of maximum power transmitted and the maximum transmission efficiency for the wireless charging system with serial-serial structure.It means the operating point of achieving the maximum transmitted power does not coincide with the one for maximum efficiency.The result of above analysis becomes the foundation for following design and implementation of magnetic coupling coils and high-frequency inverter power supplies for wireless charging systems.During design phase,meticulous study is dedicated to perspectives such as topology candidates for high-frequency inverters,the working principle,selection of switching devices,power consumption of MOSFET,EMI issues due to optimization for power consumption,control circuit design for the full-bridge MOSFET circuit,configuration for control on dead-zone of chipset,driver circuit design for full-bridge MOSFET circuit,circuit design to accelerate switching MOSFET off,bootstrap circuit design,etc.Feasibility of the design concept is confirmed with the results from experiment,in which critical waveforms of aforementioned module are captured with oscilloscope and measurements are then analyzed.The effectiveness of wireless charging system depends not only on the quality of circuit implementation of system itself,but also heavily on output capability of the power supply,the transmission distance,the offset between the coupling coils,and the application scenario.In order to explore the details on their relationships,a low-frequency(fixed-frequency)wireless charging system experiment platform with application on loads of low equivalent resistance was built according to the subject requirements during the research work.This platform facilitates a large number of experiments to study the relationship between transmission characteristic of the wireless power transmission based on magnetic coupling resonance system and different loads,transmission distances,and horizontal offsets.Finally,the system can achieve wireless transmission performance of high efficiency with following specification: transmitting power of 420 W to the end at working frequency of 50 kHz,load of 50Ω,distance of 135 mm,and efficiency of 80% above when distance is 100mm;transmitting power of 280 W to the end at working frequency of 50 kHz,load of 20Ω,distance of 135 mm,efficiency of 85% above when distance is 100mm;transmitting power of 240 W at working frequency of 50 kHz,load of 5Ω,distance of 180 mm,and efficiency of 90% above when distance is 100 mm.Through the research and analysis of the above experiment,together with the experiment on voltage regulation,the system can generate a stable dc voltage output of 12 V,when the relative motion between transmitting and receiving coils is within a limited range.It therefore improves the flexibility of the system application.