Research On Auxiliary Coil Detection Technology For Wireless Power Transfer Systems

Wireless Power Transfer(WPT)technology enables high reliability and high insulation requirements for power transfer under non-contact conditions.Its advantages such as convenience,safety,and ease of automation improve the safety of electrical equipment and user experience.Currently,WPT systems are gradually developing towards high frequency and high power.Since the alternating magnetic field is open,the system needs to have the ability to detect various types of foreign objects(metals,living organisms,etc.)to ensure safety and reliability during power transmission and prevent electromagnetic leakage from harming biological organisms.In addition,voltage or current phase deviation caused by position offset has a critical impact on the active rectification control of the receiving end.Therefore,studying foreign object detection and position offset detection is crucial for the efficiency,stability,and electromagnetic compatibility of coupled transmission processes.This article analyzes the existing foreign object detection and position detection methods both domestically and abroad.Based on the impact of foreign object intervention and position offset on the WPT system,a foreign object detection method based on measuring the electromagnetic energy transfer changes between resonant detection coils and a position offset detection method based on decoupling auxiliary coils are proposed.Firstly,theoretical derivation and simulation analysis are carried out for the foreign object detection scheme to determine that the method uses changes in the electromagnetic energy transfer between detection coils caused by foreign objects to achieve detection.Unlike traditional signal detection methods based on impedance or resonance frequency changes,even if the foreign object is small,the resonance detection coils in the array will become detuned,causing significant changes in the electromagnetic energy transfer between the detection coils,which can be measured sensitively.Finally,it is verified by simulation that a vertically arranged coil array can achieve decoupling with the power-level coupled coil.Secondly,in order to address the issues of magnetic coupling structure position deviation and switch phase control of the active rectifier in the MHz-WPT system,this paper proposes an auxiliary coil design with decoupling characteristics,combined with the 6.78 MHz push-pull Class E rectifier’s feature of constant phase shift independent of load.The design also achieves position deviation awareness and voltage-current phase detection.Due to its decoupling characteristic,it can effectively suppress electromagnetic interference on the receiving coil current,and thus the auxiliary coil serves as a mapping transmitting coil,avoiding unexpected phase shift caused by position deviation and load variation,and achieving high stability of displacement sensing and phase detection at the receiving end.Compared with the conventional method of using current transformers,this method can be used at higher operating frequencies.To validate the performance of the proposed foreign object detection coil and position offset detection coil,an experimental platform for foreign object detection and position detection was constructed in this paper.The experimental results showed that the proposed foreign object detection coil and method can achieve decoupling with the power level coupling coil and accurately detect small-sized foreign objects.The parameters of the proposed decoupling position detection coil can match well with the position offset,achieving high stability,low cost,and small volume position offset detection.It can also detect switch phases that are unrelated to the receiver’s motion.Additionally,the two detection coils are decoupled in terms of magnetism and do not interfere with each other.