Constant voltage type dynamic wireless charging and metal object detection system using resonance

Abstract

In this dissertation, the safety problem of electric vehicle (EV) wireless chargers, which has attracted much attention recently, has been dealt with. Inductive power transfer system (IPTs) has been used generally for EV wireless chargers but IPTs generates strong electromagnetic field (EMF), which can badly affect living objects such as cats, dogs, etc. Many solutions to solve the EMF problem of wireless power transfer system (WPTs) have been proposed. Among the many solutions, the solutions for dynamic wireless charging system has been proposed but the proposed solution has some disadvantage, which is to be expensive and complex. The dynamic wireless charging system, which can solve EMF problem and be simple and cheap, has been proposed in this paper. There is another problem of EV wireless chargers, which is caused by metal objects. During wireless charging, if a metal object enters between transmitter (Tx) pad and receiver (Rx) pad of wireless charger, eddy current is induced by strong magnetic field of Tx pad and temperature of the metal will increase, which can cause a fire accident and damage to the wireless charger. Many methods have been proposed to solve this problem but those are difficult to apply to high power wireless charging system or much costed. The method using magnetic field change has been studied as the promising but has some dead-zone, which means where metal objects cannot be detect. A method, which can detect the all area on Tx pad by simple way, has been proposed in this paper. Chapter 1 introduces constant type dynamic wireless charging system. The method, which can simply solve EMF problem without complex control system, is proposed. The difference between when there is Rx coil and when there is no Rx coil is used in the proposed method. The proposed method is verified by simulation and experiment. In the experiment, the Tx coil current difference between when there is Rx coil and when there is no Rx coil has been 1.5 times so the possibility of proposed system has been verified. Chapter 2 proposes metal object detection (MOD) system for EV wireless chargers. The proposed MOD system has independent voltage source differently with previously proposed method using magnetic field change and can detect small metal objects because the inductance variation by metal objects is maximized by resonant circuit. The proposed system is verified by simulation and experiment. In the experiment, the voltage variation due to 2cm x 2cm metal object has been about 500mV and 2 channel operation has been confirmed.