High-efficiency Wireless Power Transfer System And Receiver Circuit Design

Wireless power transfer has a history of more than 100 years.After years of development,wireless power transfer has been able to transfer several microwatts,several watts,or even several kilowatts of power to different devices in practical applications.However,no large-scale use has yet been made in practical applications limited by efficiency.How to improve efficiency has always been the research focus of wireless power transfer.The efficiency of the wireless power transfer system is determined by the efficiency of inverter,coil transmission,rectifier and regulator.Usually,coil transmission efficiency is the most critical factor affecting system efficiency.In the practical application,the coupling coefficient changes due to the positional uncertainty between the transmitting coil and the receiving coil,and the load of the receiver also changes with different applications.For example,the impedance of the battery may change in the process of charging.Both of these uncertainties can seriously reduce transmission efficiency.In fact,the transmission efficiency in the wireless power transfer system has an optimal value.The necessary condition for realizing the optimum value is that the load of the system is an optimal load.The optimum load value is related to the coupling coefficient between the coils,which means that the optimal load value is an uncertain value.In order to solve this problem and achieve optimal efficiency,this paper analyzes the two-coil wireless power transfer system with series-series structure,and derives the important characteristics of the maximum transmission efficiency point based on the basic circuit equations.By innovatively using these characteristics to construct a criterion for determining the maximum efficiency point,a low-cost maximum efficiency point tracking method based on the principle of impedance transformation is proposed,and the system load can be converted into the optimal load value in real time.This method to overcome the uncertainty of optimal load does not require additional instruments such as power meters.This paper also extends the applicable circuit topology of the proposed method.In order to verify the effectiveness of the proposed method,the board-level circuit is designed for verification.The experimental result shows that the proposed method can effectively improve the transmission efficiency,ignoring the changes of the coupling coefficient and the system load.After optimizing the transmission efficiency at the system level,this paper improves the efficiency of the rectifier and regulator at the circuit level.By integrating an active rectifier on the chip,an off-chip passive rectifier can be replaced so the efficiency of rectifier is increased.This paper also analyzes the limit-cycle oscillation phenomenon when the rectifier control circuit synchronizes.By redesigning the synchronous circuit structure,the output voltage ripple is reduced.