| Wireless power transmission is a new contactless power transmission technology,has received wide attention in recent years.Wireless power transmission is mainly of two types: magnetic induction and magnetically coupled resonance.The former working process is similar to the hollow transformer.When its transmission distance increases,the efficiency decreases dramatically.The latter uses the principle of resonance,which can maintain high transmission efficiency and power transmission in the long distance.In this paper,characteristics and circuit of the magnetic coupled resonant wireless energy transmission system are studied.The transmission principle of the magnetic coupled resonant wireless power transmission system is modeled and analyzed using the T model of transformer.This paper deduced the relationship between system transmission performance and operating frequency.And the relationship between transmission performance of system and load,the working frequency is determined.When the system is in the resonance state,the transmission performance is best.And when system impedance is equal to the conjugate of the load impedance,the output power is maximum.At the same time,the series-parallel connection mode of the coil is analyzed.The capacitance of transmitting coil and receiving coil is selected as series connection mode.The magnetically coupled resonant wireless power transmission system works on megahertz frequency,so the requirement for the performance of inverter is higher.Generally an E-class inverter is chosen as a power supply for the system.In order to make a higher degree sine wave output,reduce harmonics and output higher power under the same conditions,high frequency heating power supply can be used for reference and the power topology of double E-class inverter is selected.The working principle is analyzed,and a method to determine the design power parameters is found,which is based on the output power and quality factor.According to the results,a drive circuit and double E-class inverter used DSP28335 to control the working state is designed,then the output characteristics and its internal impedance of the inverter is measured.Three different types of coils included planar spiral coil,hollow cylinder coil and planar rectangular coil,are simulated and analyzed using three-dimensional modeling of electromagnetic simulation software HFSS.Compared the transmission performance of the three kinds of coils,the transmission performance of the hollow cylindrical coil is the best at long distance.The transmission characteristics of the two coils structure system were measured and analyzed.By changing the operating frequency and load of the two coil wireless power transmission system,the values of the input and output power are measured.The frequency characteristics and load characteristics of the system are obtained.The results shows that the maximum transmission efficiency is obtained when the system is in the state of resonance and the maximum transmission power are obtained when the load is matched.Due to the production process,measurement errors and high-frequency interference,the parameters of transmit and receive coils are inconsistent.The two coils cannot in the resonance state at the same time and it affects the transmission performance.In order to solve the problem,a control strategy based on frequency tracking and MPPT switching capacitor compensation is proposed,and the results are simulated and analyzed. |
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