| Magnetically coupled resonant radio energy transmission technology stands out in the wireless energy transmission technology because of its excellent characteristics,and has become a hot technology at the current global research point.This technology can realize far-distance transmission distance through the resonant coupling of the inductor coil,and make up for the defects in the wireless energy transmission technology.However,there are still a series of urgent problems to be solved in the technology:The system is subject to external obstacles,load changes,changes in transmission distance and coil offset,which cause the circuit to be detuned,resulting in a sharp drop in transmission power and transmission efficiency,affecting the transmission performance of the system.In view of the above problems,this paper studies the frequency characteristics of the system circuit at maximum transmission power and transmission efficiency,and simulates and optimizes the design of the space magnetic field,inverter power supply and resonant frequency tracking of the system circuit,further improving the system transmission power and efficiency.Main tasks as follows:(1)The principle of magnetically coupled resonant radio energy transmission circuit is analyzed.The mathematical model of the circuit is established by using the circuit mutual inductance theory.The expressions of the output power and transmission efficiency of the secondary circuit are derived.The frequency splitting characteristic curves of the system under different coupling coefficients and quality factors are obtained.It is concluded that the maximum transmission power and the maximum transmission efficiency frequency of the circuit are inconsistent in the case of over-coupling and high quality factor.(2)Based on the electromagnetic field as the guiding theory,the influences of different winding structures and winding turns on the inductance value and mutual inductance value are analyzed.The 3D finite element model of the transmitting coil is established by ANSYS.The transmitting coil model is solved by the edge element method.The distribution law of the magnetic field intensity generated by the transmitting coil in space is obtained,which provides a theoretical basis for designing the magnetic coupling mechanism.(3)According to the high-frequency inverter power supply required by the circuit,a class E inverter circuit with high inverter efficiency is designed.The working principle and optimal working state are analyzed,and the design formula of the main power circuit is derived,the circuit parameters are calculated based on the optimal load.The main circuit is simulated by the MULTISIM software platform.the circuit soft switching waveform is ideal and the loss is low.It can be used as the main power circuit of the magnetic coupling resonant radio energy transmission circuit.(4)Aiming at the problem of resonance frequency drift,a digital phase-locked loop circuit based on FPGA is proposed to track the current-voltage phase signal of the resonant coil,ensure that the circuit works in a resonant state.The phase detector,loop filter and numerically controlled oscillator of the digital phase-locked loop circuit are designed,the Verilog HDL code is written,the phase-locked loop circuit is simulated and verified by the Quartus platform.The simulation results show that when there is an initial frequency difference between the input signal frequency and the natural signal frequency,the steady-state phase difference can reach zero after the loop lock,and the frequency tracking can be realized.Finally,a small power frequency tracking type radio energy transmission device is developed,and comparative experiments and no-load experiments are carried out.The experimental results show that the maximum transmission distance reaches 25 cm.The maximum transmission power is 16.92 W at 5cm,and the maximum transmission efficiency is 72%,transmission power and transmission efficiency are improved compared to circuits without frequency tracking. |
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