Analysis and Design of Three-Coil Structure WPT System With Constant Output Current and Voltage for Battery Charging Applications

Lin Yang,Pilong Guo,Sheng Liu,Ziwei Xu,Changsong Cai,Xiaoming Li

doi:10.1109/access.2019.2925388

Lin Yang, Pilong Guo + Show 4 more

Open Access

https://doi.org/10.1109/access.2019.2925388

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Abstract

Compared with the traditional plug-in charging system, the wireless charging system for battery charging has broad application prospects due to its significant advantages, such as security, convenience, and aesthetics. In practical applications, in order to prolong the battery lifecycles, it is preferred to charge the battery with constant current (CC) and constant voltage (CV) modes. However, since the battery equivalent resistance varies greatly during charging, it is not easy to design a complete charging system owning CC and CV output characteristics. Besides, the equivalent input impedance of the system is preferably resistive to improve efficiency and enhance power transfer capability; therefore, achieving the zero phase angle (ZPA) operation is extremely important. Hence, a novel three-coil structure WPT system is proposed in this paper to solve the above issues. A comprehensive theoretical analysis for the three-coil system to realize the CC and CV charging modes with perfect ZPA operation at two fixed operating frequencies is presented. Furthermore, due to the parasitic losses of passive components and the instability of the dc input voltage, it is unrealistic to achieve accurate and stable CC and CV outputs through the inherent properties of the circuit itself. Consequently, a simple closed-loop controller is introduced into the system to enable the desired CC and CV charging characteristics with zero voltage switching (ZVS) operation by slightly adjusting the operating frequency. Finally, a confirmatory experimental prototype with 4.6-A charging current and 56-V charging voltage is fabricated to confirm the feasibility and validity of the proposed method. The experimental results agree well with the theoretical analysis.

Highlights

The wireless power transfer technology, which can transfer electrical energy to the load through magnetic field without twisted electrical wires, is undergoing rapid development in recent decades due to its crucial merit of safety, convenience, isolation, etc
To overcome the disadvantages of the control complexity and instability caused by the above-mentioned three control schemes, as well as the drawbacks of the high cost and increased volume/weight caused by the hybrid topology, this paper proposes a novel three-coil structure WPT system to achieve the constant current (CC) and constant voltage (CV) charging modes with the zero phase angle (ZPA) operation of the high-frequency inverter (HFI) at two different operating frequencies, respectively
DESIGN OF THE CLOSED-LOOP CONTROLLER FOR THE CC/CV CHARGING MODE Once the three-coil WPT system is properly designed based on the design procedures mentioned in Fig.4, the CC and CV output characteristics can be readily realized without closed-loop controller at two different operating frequencies, respectively

Summary

INTRODUCTION

The wireless power transfer technology, which can transfer electrical energy to the load through magnetic field without twisted electrical wires, is undergoing rapid development in recent decades due to its crucial merit of safety, convenience, isolation, etc. In order to avoid the above-mentioned drawbacks of the PSM and FCC technologies, an extra DC-DC converter (such as Buck, Boost and Buck-Boost circuit) is cascaded at the transmitter or receiver of the WPT system to adjust the charging current or voltage of the battery [14], [15] This method increases the component counts, extra weight/cost and the associated power losses. To overcome the disadvantages of the control complexity and instability caused by the above-mentioned three control schemes, as well as the drawbacks of the high cost and increased volume/weight caused by the hybrid topology, this paper proposes a novel three-coil structure WPT system to achieve the CC and CV charging modes with the ZPA operation of the HFI at two different operating frequencies, respectively. The following analysis of this section focuses on the load-independent CC/CV output characteristics of the proposed three-coil structure WPT system and the related ZPA operation

ANALYSIS OF THE CV CHARGING MODE

ANALYSIS OF THE CC CHARGING MODE WITH THE ZPA CONDITION

Findings

CONCLUSION