Research And Implementation Of Foreign Object Detection Method Based On Electromagnetic Induction Wireless Charging

As an emerging charging method,wireless charging technology is becoming more and more popular which uses magnetic field coupling to supply power to electrical equipment.Wireless charging can be charged at any time,and avoids frequent plugging and unplugging of the charger,thus greatly improving the user experience.But new problems follow.When the transmitter transmits power to the receiver,if metal foreign objects are mixed between the charging coils,which will affect the output power and transmission efficiency of the system as the parameters of the coil change,And because of the eddy current effect,the temperature of metal foreign bodies will rise sharply,even damage the equipment and cause fire.This article will implement two foreign object detection(FOD)algorithms based on these factors,included based on the electromagnetic induction wireless charging system,including FOD based on the quality factor Q and FOD based on power loss,for stable charging and charging of the system Provide guarantee for the security.This article is based on the electromagnetic induction wireless charging system,combined with Qi V1.2.4 protocol to understand the wireless charging system structure,establish a circuit model to study the principle of wireless charging.Based on the principle of wireless charging,a circuit model and a magnetic field equivalent diagram are established to study the influence of non-ferromagnetic and ferromagnetic metal foreign objects on the system.Multisim is used to simulate and verify.The results show that after the metal foreign objects enter the system,the quality factor and output power of the system are both Will be reduced,it is determined that the quality factor Q and system power loss can be measured to determine whether there is a metal foreign body in the system.On this basis,several foreign body detection algorithms applied to the system are proposed.The first is FOD based on the quality factor Q.Two methods for measuring the quality factor Q when implementing this algorithm are studied.The article mainly focuses on the underdamped oscillation method to measure the quality factor Q.Carry out research,obtain the correlation function of quality factor Q through theoretical calculation and formula derivation,and use this method to measure the system quality factor Q with or without metal foreign matter to compare the system quality factor Q to determine the feasibility of the algorithm.Then,the relevant formulas are converted to obtain a measurement method suitable for this system-the discrete method,and the algorithm is evaluated through theoretical calculations and actual tests,and the algorithm error and implementation method are determined.The second is based on the power loss FOD,the basic principle of the algorithm and the implementation process are studied,and the system power loss is measured when there is a metal foreign body in the system.The results show that the system power loss increases significantly when there is a metal foreign body compared to when there is no metal foreign body.The hardware control circuit and software control process are designed based on the research and analysis of the algorithm,and the hardware platform is built for debugging and testing.The first debugging purpose is to confirm the receiving power compensation method in the power loss method,put forward a linear compensation method,and give the compensation coefficient and compensation formula.After compensation by this method,the maximum difference between the transmitting power and the receiving power of the system is 467 mw,which is within the acceptable range;the second debugging purpose is to determine the quality factor Q based FOD Through testing the quality factor changes of the system after different foreign bodies enter the system,the Q threshold is obtained according to the data.Finally,test the FOD function of the system.The test shows that the system can detect several metal foreign objects provided in the center position without affecting normal communication,and can detect the metal foreign objects of a one-yuan coin with an offset of 35 mm from the center,which proves that the FOD function of the system achieves the expected effect.