| Wireless power transmission is a technology that can transmit electricity from the power source to the load rely on energy carriers in the space instead of wire within a distance,which provides greater security for power supply in harsh environments and at the same time makes the power utilization in daily life more convenient.Among the wireless power transmission technologies,although the magnetic resonance coupling technology started relatively late,owing to the high-efficiency at medium distance and has little impact on living organisms,it has a board research and application prospect.This thesis conducts research on wireless power transmission system with series-parallel topology via magnetic resonance coupling,combining theoretical analysis,simulations and experiments to study the characteristics of system,proposed related optimization methods focus on the frequency splitting and detuning phenomenon of system then verified their effectiveness.The main contents and improvements are as follows:(1)Based on the mutual inductance theory,the equivalent circuit model was established for series-parallel system.The expressions of compensation capacitance at both sides were obtained so the reasons why the system detune were found out,then the expressions of output power and efficiency were obtained as well,which shows that series-parallel model has the characteristic of constant voltage output which is load independent,through the analysis of frequency splitting and frequency bifurcation phenomenon,the conditions of their occurrence were found out,then put forward the fundamental reason why the phenomenon appears is the mismatch of load resistance under the coupling state of coils.(2)Through theoretical analysis,the frequency characteristics of the system were studied by the MATLAB,the results show that it has strong selectivity to the frequency of power injected to the system and both the output power and the efficiency achieve at the maximum value at resonant frequency under the normal mode and the output power is more sensitive to the frequency changes than the efficiency,then studied the influence of various parameters relate to the system's frequency selectivity,the relationship between frequency splitting and frequency bifurcation and their characteristics.On this basis studied the parameters that relate to the energy efficiency characteristics in order to find how they influence the output power and efficiency of the system in resonance,and then took a research on parametiric sensivity of the system's power transmission,since the parameter offset often causes the system to be detuned and thus reduce the output power,it comes to a conclusion that the direction of system optimization is to suppress frequency splitting,to implement the adjustable of input voltage frequency and frequency tracking method.(3)After accomplishing the construction of resonant network according to performeance indicators,aiming at the critical load in the current coupling state of system,a method of introducing an type-L impedance adjustment network at receiver to suppress frequency splitting phenomenon was proposed,the introduction of DSP realized the adjustment of input voltage frequency using external keyboard and a frequency tracking method based on the average value of sampling current when the voltage at commutation point was also realized to implement the optimization of system.(4)After studying the frequency and power transmission characteristics based on the experimental platform,the results show the correctness of the theoretical derivation and simulations,the optimization methods are also effective.Through the comparision of the series-series system and the series-parallel system,it comes to a conclusion that the resonant frequency of series-parallel model is more susceptible by parameters but it has better output characteristic,finally a relay coil was introduced into the system,which proves that the relay coil can still achieve electrical relay transmission in the series-parallel system. |
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