The Desigh Of A Lithium Batterey Charger Based On WPT Technology

In recent years, as a new way of power transmission, Wireless Power Transmission(WPT) technology receives more and more attention. Compared with the traditional way by using wires for power transmission, WPT technology doesn’t need metal connection,thus it can avoid the direct electrical connection between the electrical equipment and power supply side, and based on this feature, the WPT technology has great application prospects in some occasions with higher requirements for safety and convenience, such as chemical industry, mine, underwater and medical apparatus and instruments, etc. This paper mainly designs a lithium battery charger based on WPT technology, and it can charge the battery with constant current in first stage and constant voltage in the second stage(CC- CV).Firstly, significance of the research and present situation of WPT at home and abroad are proposed in this paper.Then, by comparing the implementations of WPT, the inductive coupling wireless power transmission is chosen. The mutual inductance model of the loosely coupled transformer is established and the compensation structures are introduced to improve the system performance. In addition, the compensation capacitor, voltage gain, transmission efficiency and frequency bifurcation are analyzed in detail.Three kinds of batteries are introduced and lithium-ion battery is chosen as charging object. By analyzing operating principles and charging characteristics of lithium battery,multi-step charge strategy is decided to shorten the charging time. That is, battery is charged by constant electric current, and then with constant voltage. For simplify, a variable resistor model is used instead of lithium battery.The key parameters, such as primary- and secondary- windings, compensation capacitors and resonance frequency, can be designed. Charging the battery with constant current in first stage and constant voltage in the second stage(CC- CV) is simulated by PSIM or MATLAB.The constant-voltage output of receiving terminal without voltage regulation circuit is realized in the case of varying loads, which validates the correctnessof theoretical analysis and the reasonability of design process.Finally, the hardware circuits of the wireless power transmission system which consist of main circuit, control circuit and protection circuit are designed. The transformer is designed in detail. Moreover, the choice of the components in main circuit are given, the chips in control circuit and protection circuit are also introduced. The protection circuit achieves the overvoltage protection of MOSFET and overcurrent protection, which insures the reliable and stable operation.