Research On Constant Current And Constant Voltage Based On LCL-S For Wireless Power Transfer System

Wireless Power Transfer(WPT)is a special way of transmitting electricity.WPT is gradually being applied to various fields as a non-contact power supply method and has become the focus of current research.The commonly used wire transmission cannot avoid problems such as clutter,ageing and electric sparks.WPT has the advantages of high security,portability,flexibility and adaptability,and is a change in the new power supply method of the future.It can be widely used for charging batteries of electric bicycles,cars,etc.In order to better protect the battery WPT charging,a combination of Constant Voltage(CV)and Constant Current(CC)modes is used to meet the battery charging characteristics for the overcurrent and undervoltage problems encountered during charging.Firstly,the background and significance of WPT research is introduced,and the transmission principle and current status of WPT research are analysed.Based on magnetically coupled resonant wireless energy transmission,this paper presents a theoretical derivation of LC resonant circuits and uses an equivalent circuit model to analyse the advantages and disadvantages of different resonant compensation topologies.It is concluded that S-S and S-P have constant current and constant voltage output characteristics under certain conditions,respectively.In order to avoid frequency bifurcation,the LCL structure with higher resonant capacity and lower voltage stress is chosen as the primary side compensation network.Next,based on the circuit principle and mutual inductance coupling model,the LCL-S compensation network is proposed on the basis of the LCL resonant network topology and its output characteristics are analysed.Compared to the conventional LCL circuit,the primary side is used to switch the compensation capacitor by adding an AC switch,and the secondary side adopts a series-compensation structure to achieve a constant voltage and constant current charging independent of the load.The advantage of this solution is that it switches between constant voltage and constant current operating modes at a fixed frequency,only needs to detect the voltage at the load side and compare it with the set value,and the control scheme is simple.The focus is on the structural design of the coupling coil and the simulation design using Maxwell software.The hardware platform,wireless communication and software control strategy of the system are introduced.The simulation circuit model is also built by MATLAB/Simulink and the simulation experimental waveforms are analysed.Finally,the feasibility of the proposed scheme is verified by building an experimental prototype of wireless energy transmission with 55 v DC power supply and 24 V output on the load,which can achieve constant voltage 24 V output and constant current 5A charging by changing the charging mode by switching the compensation capacitor.The system has zero voltage turn-on(ZVS)during constant current charging,which reduces switching losses,and Zero phase angle(ZPA)operation during constant voltage charging,almost no reactive power losses.