Research

My current research interests include all general topics related to power electronics, especially wireless power (WPT) transfer for high power applications. During my studies, I have carried several projects on WPT for Electric Vehicle Battery Charging, both of Static and Dynamic Chargers. I only mentioned the finished works here (most in Master period), ongoing works will be updated later.

1. Implementation of the CC/CV Charge of the Wireless Power Transfer System for Electric Vehicle Battery Charge Applications

Target applications: medium and high power for Electric Vehicle Battery Charger.

Period: Mar 2015 – Feb 2016

Abstract: When compared to plugged-in chargers, Inductive Power Transfer (IPT) methods for Electric Vehicle (EV) battery chargers have several benefits such as greater convenience and higher safety. In an EV, the battery is an indispensable component and Lithium-Ion batteries are identified as the most competitive candidate to be used in EVs due to their high power density, long cycle life and better safety. In order to charge Lithium-Ion batteries, Constant Current/Constant Voltage (CC/CV) is often adopted for high efficiency charging and sufficient protection. However, it is not easy to design an IPT Battery Charger that can charge the batteries with a CC/CV charge due to the wide range of load variations, which causes a wide range of variation in its operating frequency or duty. Furthermore, Zero Phase Angle (ZPA) condition for the inverter cannot be achieved over the entire charge process without the help of additional switches and related control circuits to transform the topology. This project suggests a novel method which makes it possible to implement the CC/CV mode charge with minimum frequency variation (less than 1 kHz) during the entire charge process by using the load-independent characteristics of an IPT converter under the ZPA condition without any additional components. The proposed method is advantageous in that the efficiency of the converter is very high due to the perfect resonant operation during the entire charge process. A theoretical analysis is presented to provide the appropriate procedure to design the resonant tank which can achieve CC and CV mode charge under ZPA condition with a double-sided LCC compensation topology. A 6.6 kW prototype charger has been implemented to demonstrate the feasibility and validity of the proposed method. A maximum efficiency of 96.1% has been achieved with a 200mm airgap at 6.6 kW during the CC mode charge.

Fig. 3. Efficiency curves indicate high efficiency achieving in both CC and CV modes Fig. 4. Double-sided LCC topology for high power wireless power transfer system

2. Design and Implementation of the Constant Current and Constant Voltage Charge of the 6.78 MHz Wireless Charger

Target applications: low power (several watts up to 100 watts) for electronic devices: mobile phones, robot cleaner, IoT system, etc.

Period: Mar 2016– Aug 2016

Abstract: Wireless Power Transfer (WPT) has received a great interest recently since its advantages such as higher user convenience and better safety as compared to conventional charging with cord. In a WPT charging system operating at MHz range, there is always required of the DC/DC converter at charging device to provide the exact value of voltage and current to the battery. This paper proposes a design and implementation of a high frequency Wireless Power Transfer system with Constant Current (CC) and Constant Voltage (CV) Charge for Lithium battery applications. The charger can implement CC/CV charge without any extra DC/DC circuit at fixed operating frequency. The simulation and experimental results are presented to verify the analysis and evaluate the performance of the proposed battery charger.

Fig. 1. The proposed circuit diagram for 6.78-MHz and low power Wireless Power Transfer.

Fig. 2. Control and Driver circuit for prototype Fig. 3. Some initial results in CC mode

Please note that I have proposed whole idea and design consideration in this work. However, as the funding has been running out at this time, then I could not continue this project after August, 2016. At the moment, this work is continuously carried out by one of the member of RECL Lab, Soongsil University, South Korea. Fig. 2 and 3 above were provided by this member.

3. Dynamic Charging for Electric Vehicles (EV) by Wireless Power Transfer

Target applications: medium power (up to 3 kW) for EVs battery charger. The vehicle moves along transmitter and battery on-board is charged simultaneously.

Period: Oct 2016-present

Abstract: A dynamic charging system with stable output power along the driving direction for high power Electric Vehicles (EVs) battery charging is newly suggested in this paper. Multiple transmitters combining with alternative magnetic poles in long-track form are adopted at the primary side to energize a number of receivers. Structure layout for a number of transmitters is proposed and theoretical analysis is conducted to draw conditions of each transmitter’s current for achieving constant output power in secondary load. In addition, negative effects on primary inverter of the crossing mutual inductances between transmitters have been nearly neglected in the proposed layout. Next, three phase inverter is adopted to provide high frequency currents for three transmitters as demonstration. To simplify control of transmitter currents, several primary LCC compensation tanks are selected. The proposed system has advantageous of removing the presence of sensor and control circuit in order to control the transmitter currents, minimizing number of primary inverters and being able to energize multiple receivers simultaneously. The proposed system’s performance is verified by both simulation and experimental results.

This project is still on progress. Keep updating.