| Wireless power transfer(referred WPT) is a kind of power transmission technology which transfer power from power source to load across an air-gap on physical medium. It has the advantages of flexibility, safety, easy maintenance, etc.Products such as electronic consumption, appliances, vehicles are applied more and more. With electric vehicle generalized and popularized, it will show good prospect.The thesis is based on the object of WPT system which adopts series-parallel compensation structure, through the means of theoretical analysis,the equivalent mutual inductance model,computer simulation to study the two questions of maximum power transfer and suppressing electromagnetic interference(EMI) of WPT system. Its main contents are as follows:⑴ Several kinds of technical approaches and their characteristics, the research status, the major tasks and the significance of the article are introduced. In order to establish the research subject, the structure, selection and design of each circuit are depicted. The entire model of WPT system is built and verified.⑵ The key point of WPT system to achieve maximum power transfer is adopting compensation network. Multi-resonance isn’t helpful for system control.The effect of several main parameters variation on output power is studied. The primary-side zero-phase angle frequency and bifurcation criteria is analysised.Transfer function of WPT system is deduced. The reason of multi-resonance generating is explained.⑶ Because of the problems of parameter tolerance, manufacturing accuracy,consistency etc, they cause deviation of the maximum power transmission point.The thesis put forward a new and original way to calculate directly the maximum power transfer point by only detecting transmitting coil voltage and current without any wired or wireless feedback from secondary side. The scheme is verified by simulation.⑷ In order to solve the problem that transmitting/receiving coil current of WPTsystem with the fixed frequency pulse width modulation(PWM) has high level of electromagnetic interference around its space, the spread spectrum technology which suppresses the electromagnetic interference at its source is proposed. Frequency jitter,periodic modulation, chaotic modulation are respectively applied to wireless charging system. The simulation results demonstrate that all of them can decrease the harmonics peak value. The better effect in turn is chaotic modulation, periodic modulation and frequency jitter.The conclusions and means have a certain theoretical value and practical significance. |
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