| Inductive power transfer technology is an emerging power supply technology,which is based on the principle of electromagnetic induction,and owns the features such as no restriction of space,convenience,safety,reliability and so on.And in recent years,the promotion of electric vehicles has made EV wireless charging technology a research hotpot.On the basis of the background,in this paper,a wireless power transfer system of medium power with a phase-shift full bridge connected on the output side is studied.And based on extensive researches,DC/DC circuit,resonant network,power regulation method on the primary side,and control method of the whole system are mainly analyzed and designed.Firstly,PSFB is chosen as the DC/DC circuit,and its operating process,characteristics,and the condition of zero voltage switch are studied.And the small signal modeling is made.Secondly,the input/output characteristics and optimal load of commonly-used resonant circuits are studied and summarized.Meanwhile the differences of LCL-T-type and P-type resonant networks are compared.When the resonant circuit is selected according to the system requirements,to aim at optimizing the efficiency at rated load,an S-type resonant circuit is connected in series.This resonant circuit is called S-LCC-type resonant network,which can change the optimal load to match the rated load.The change of the characteristics of the circuit with/without S-type is also discussed.Thirdly,operating process and equivalent input impendence of the rectifier connected behind the S-LCC-type resonant network is analyzed.Based on the fundamental wave analysis,the power regulating capability of three pulse width modulation control methods is discussed,as well as realization of soft-switching under the working condition of the system.To achieve ZVS of every switch,composite pulse density modulation is used here,and the influence of control cycle on the efficiency is discussed through simulation.Fourthly,the control strategy is set aiming for the efficiency of the whole system,in which the PSFB controls the output voltage,and the primary controller adjusts the input resistance of PSFB.When this strategy is used,the resonant network can work at high efficiency,while ZVS of PSFB can be realized,to achieve optimal efficiency.On the basis of the above theoretical analysis,hardware and software are designed to complete the system prototype and achieve its operation.The experiments show that efficiency is higher when using CPDM control than that when using phase shift control,and efficiency is higher when adding primary control than that when using only FSFB controller.Under the condition that air gap is 20 cm,the output power of the system is about 1500 W,efficiency of inductive power transfer part is about 83%(from dc input to recitifier output),and the total efficiency is about 75%(dc voltage input),which meet the theoretical expectations. |
