| Wireless power transmission is a cross-disciplinary research field including electromagnetic field,power electronics technology,physics,materials science,circuit and modern control theory.It can effectively overcome the problems existing in traditional power supply,such as poor flexibility,environmental unsightly,electric spark,power supply line exposure,etc.,to eliminate safety hazards and make power transmission more flexible and safer.It has broad application prospects in the fields of electric vehicles,aerospace,military,oilfield mines,underwater operations,household appliances and medical devices.Wireless power transmission system is a typical multi-parameter and detuning system.In the process of its development,there are still the following problems:The change of system structure parameters will lead to the decrease of transmission efficiency and performance.Modeling and analysis of magnetically coupled resonance system is complex and low accuracy.The change of coupling leads to frequency splitting and transmission efficiency reduction.Mistuning and impedance matching affect power transmission and efficiency.It is difficult for both transmitters and receivers to control cooperatively,especially when the load changes dynamically,which results in the reduction of transmission efficiency.In order to solve the above problems,this dissertation mainly focuses on the following aspects:(1)The transmission mechanism and characteristics of different coupling modes are studied based on the theory of circuit reflection.Through simulation and analysis of magnetic field distribution,the influence of system structure and parameters on transmission characteristics is obtained.A new method of system structure optimization based on dual-mode cooperative work is proposed,which can switch the system structure under different application conditions,thus improving the application scope of wireless power transmission system.(2)Research on the resonance and power transfer characteristics of the system by using scattering matrix,and a method for analyzing the electromagnetic coupling efficiency using the generalized coupling matrix is proposed.A generalized coupling matrix model of the system and a new method of impedance matching through external coupled impedance transformation network are proposed.The generalized coupled matrix model is optimized by designing the critical coupling coefficient,and the model is extended to any(N+M)multi-coupling resonant network.(3)The model of misaligned coupling magnetic field and mutual inductance is established.Through simulation analysis,the spatial magnetic field distribution and mutual inductance characteristics of lateral and angular misalignment are studied,and the influencing factors and rules of transmission efficiency for the spatial position change of transmitter and receiver are extracted.A dynamic optimization method of misalignment coupling based on angle rotation of receiving coil is proposed,which eliminates the transmission dead zone caused by dynamic change of coil position in space.(4)The effects of coupling coefficient and load on voltage gain,current gain and transmission efficiency of different resonant compensation matching topologies are studied.An optimization method for transmission efficiency of LCC resonant compensation structure is proposed by optimizing the load coefficient and critical coupling factor.The zero phase angle(ZPA)conditions and load-independent output characteristics of different compensation topologies are studied.The effect of compensation topology on transmission characteristics is summarized through simulation analysis,which provides a new analysis idea for the design of control scheme of wireless power transmission system.(5)An integrated load estimation and power tracking control strategy based on two sides LCC compensation is proposed.Load estimation and mode judgment are carried out at the transmitter by detecting the output current of the inverter.A PI controller is designed to control the output power of the inverter by phase shift to realize constant current,constant power and constant voltage charging of the battery.The Buck-Boost converter is regulated at the receiving end for load and decoupling control to provide a standard load and charging mode switching flag for the transmitter.The simulation results show the correctness of the proposed control strategy,which can dynamically change the power output of the transmitter to meet the load requirements.(6)A wireless power transmission experiment system for the control strategy proposed was developed,and the zero-voltage switch(ZVS)operating parameters of the inverter were designed.The feasibility and superiority of the theoretical research results and control strategies proposed in this dissertation are verified by experiments. |
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