Research On Transmission Characteristics And Output Power Control Of Wireless Power Transfer System Based On Negative Resistance

As an innovative technology of power supply,wireless power transfer(WPT)technology has gained more and more attention and research.Compared with conventional wired transmission,WPT is more secure,convenient and practical.It has been applied in many fields and profoundly changed people's lives.However,the output power of the magnetic coupling WPT system is sensitive to the coupling coefficient and the load.When the coupling coefficient or the load varies,the output power of the system will fluctuate,affecting the normal operation of the electrical appliances.To solve this problem,the WPT system based on negative resistance is proposed,its circuit model is established and the transmission characteristics are analyzed in detail.On the basis of transmission characteristics,an output power stabilization control method without utilizing dual-side communication and receiving-side control is proposed.The main contents of this thesis are as follows.Firstly,the series-series compensated WPT system based on negative resistance is modeled with the circuit theory.The frequency characteristics,current and voltage gain characteristics,transmission efficiency and output power characteristics of the system under different circuit parameters are analyzed in detail,and the condition for the system tracking to the peak value of output power is pointed out.In addition,the frequency stability of WPT system based on nonlinear negative resistance is analyzed by utilizing Hamel locus function.Secondly,according to the circuit analysis results,an output power stabilization control method based on adjustable negative resistance is proposed for series-series compensated WPT system,and the rationality of this method is preliminarily verified by circuit simulation.The proposed control method includes two parts.One is the negative resistance frequency closedloop control.By automatically tracking the bifurcation frequency,a constant output power independent of the coupling coefficient is achieved within a certain transmission range,so there is no need to detect the mutual inductance values.The other one is the negative resistance voltage closed-loop control.When the load varies,the voltage of negative resistance can be automatically regulated according to the estimation results of output power and load identification,thereby achieving control of the output power.The whole control process can make the output power stabilize at different given reference values only by detecting the voltage and current at the transmitting side.Subsequently,the design method of WPT system based on the adjustable negative resistance is presented according to the theoretical analysis and control method,and the design details of the main parts of the system prototype are introduced.Finally,a prototype of WPT system based on the adjustable negative resistance is fabricated for experimental analysis and verification.The experimental results show that the prototype can stably output 200 W and 400 W with a maximum power error of 4.10% and 3.40% respectively when the coupling coefficient and loads vary in a certain range,and the maximum overall efficiency is 91.9%.The correctness and effectiveness of the proposed system and its output power control method are verified.