| Wireless power transmission technology is a kind of energy transmission technology with complete isolation of electric equipment and power,which has the advantages of high safety,high reliability and high flexibility ect..Therefore it has broad application prospects in electrical vehicles,consumer electronics and sensors etc..To the characteristics of the magnetic resonant WPT technology and the problem of reducing the efficiency because of the system parameter variation,the theoretical,the topology and control methods are studies in this paper.Which include the maximum efficiency point control method and adaptive tracking control method.The performance of WPT is improved.The frequency and load conditions of the maximum transmission efficiency of WPT are analyzed by AC equivalent circuit and decoupling equivalent circuit.And the input and output characteristics of the system are analyzed under the above conditions.To the problem that the equivalent series resistance varies with the frequency,the relationship between the efficiency and the frequency under the different sensitivity coefficient is studied by using the sensitivity coefficient of the AC resistance to the frequency as the parameter.To the problem that the equivalent series resistance varies with the resonant current,the transmission efficiency of the system is analyzed by the approximate method and numerical iteration method.In this paper,the structure of the magnetic resonant WPT system is described,and the high-frequency inverter circuit,resonant coil and output rectifier circuit are introduced emphatically.Based on the circuit structure analysis,a high efficiency open-loop experiment system is designed,which lays the experimental foundation for the control method of the closed-loop system.Although the open-loop WPT system can achieve high-efficiency energy transmission through optimization design,the output voltage and transmission efficiency of the system are significantly affected by the coupling coefficient and load resistance.In this paper,the relationship among the output voltage,the coupling coefficient and the load variation,also the relationship among the transmission efficiency,the coupling coefficient and the load variation of the WPT system are analyzed by using the theory of mutual inductance.Compared with the typical control method,the designed maximum efficiency point tracking control method can adjust the system output voltage and achieve the maximum efficiency under the condition that the transmission distance and load resistance are far from the optimal value.The detuning principle of magnetic resonance WPT system is analyzed in this paper.In order to keep the system working at the resonant frequency,a control circuit based on the fuzzy PI adaptive tracking algorithm is designed.The same phase of the output voltage and current is achieved by tracking the voltage signal of the inverter circuit and the transmitting current signal,so that the circuit is in a resonant state.The simulation and experimental results show that the system has good dynamic and static performance,and the maximum transmission efficiency can be obtained when the parameters of the adaptive tracking controller change dramatically. |
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