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This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TPEL.2016.2640314, IEEE
Transactions on Power Electronics
A Capacitive Power Transfer System with a
Mixed-resonant Topology for Constant-current
Multiple-pickup Applications
Yu-Gang Su, Member, IEEE, Shi-Yun Xie, Aiguo Patrick Hu, Senior Member, IEEE, Chun-Sen Tang,
Member, IEEE, Wei Zhou, Liang Huang
Abstract
—Capacitive Power Transfer (CPT) systems based
on high frequency electric field coupling have attracted much
attention recently due to their simplicity and low eddy-current
losses. This paper proposes a mixed-resonant topology consisted
of a Π-CLC resonant circuit on the primary side and a T-CLC
circuit on the secondary side for multiple pickups constant
current output applications. The voltage gain, current gain and
zero phase angle frequency at different operating modes of Π-
CLC and T-CLC circuits are analyzed by fundamental
frequency approximation, and the conditions leading to a
constant output current independent of loads are determined.
Based on the analysis, a design method to determine the
resonant network parameters is proposed according to the
required output current of each pickup. A prototype with three
pickups has been designed and built, and both simulation and
experimental results have demonstrated that the proposed
multiple-pickup CPT system can output a constant current at
each operating power pickup against the load variations of itself
and others.
Index Terms
—Capacitive Power Transfer (CPT), mixed-
resonant topology, multiple pickups, parameter design method
I INTRODUCTION
ireless power transfer (WPT) based on magnetic field
has received a lot of attention recently to provide
power to a widely variety of applications [1-7]. Capacitive
power transfer (CPT) employing electric field as the power
transfer medium is a new approach for achieving wireless
power supplies [8-12]. The coupling structure of a typical
CPT system consists of two pairs of metal plates, namely the
primary and pickup plates respectively [10,13-17]. The pickup
plates are coupled with the primary plates via electric filed in
between. Two coupling capacitors formed by the two pair
plates are usually compensated by a series inductor to
increase the power transfer capability.
Recently, due to the design flexibility of the coupling
structure and low eddy-current losses in the surrounding
metallic objects, CPT technologies have drawn a lot of
attention for applications in electric vehicles (EVs) battery
charging[8-9,18-20], consumer electronics, LED lighting [21-
25], etc. The output of CPT can be either a voltage source or
current source, and there is an increasing need for constant
current source applications such as battery charging, LED
driving, and welding [26-28]. And often more one power
pickups are needed to drive multiple loads simultaneously
with a single primary CPT circuit. Owing to the variations in
capacitive coupling and loads, it is a challenging task to
maintain the output of a CPT system to be constant even for
a constant voltage source. Liu et. al. proposed a soft-
switching transformer to compensate for the coupling
capacitance dynamically when the pickup moves, and
designed a primary pad with a matrix structure consisted of
multiple sub-plates to reduce the effect of coupling
misalignment. The output voltage can be maintained constant
against the positioning and alignment of the pickup on the
primary charging pad [29]. Lu et. al. proposed a double-sided
LCLC-resonant topology for electric vehicle charging
applications. The topology can effectively reduce the voltage
stress across the power switches of the inverter while
maintaining a unity power factor at the ac input [9].
Theodoridis proposed a T-LCL resonant topology in the
pickup to improve the current ratio between the output
current and the displacement current of the coupling structure,
so as to extend the load range [30]. These topologies provide
high frequency voltage to drive coupling structures and have
zero phase angle between the input voltage and the current,
which increases the transfer efficiency. However, there is no
work being reported on constant current output applications.
And the driving voltages of the coupling structure of the
previous systems vary with the load, which works fine with a
single pickup CPT system, but cannot be used for multiple
loads.
Manuscript received April 28, 2016; revised September 27, 2016; accepted
December 5, 2016.
This work was supported by the research funds for the
National Natural Science Foundation of China under Grants # 51477020, #
61573074 and Chongqing International Science and Technology
Cooperation Base Project (CSTC2015GJHZ40001).
Yu-Gang Su are with the Key Laboratory of Dependable Service
Computing in Cyber Physical Society (Chongqing University), Ministry of
Education, Chongqing, China and College of Automation, Chongqing
University, Chongqing 400044, China (e-mail: su7558@qq.com).
Shi-Yun Xie, Chun-Sen Tang and Wei Zhou are with the College of
Automation, Chongqing University, Chongqing 400044, China (e-mail:
yunshixie@qq.com, cstang@cqu.edu.cn, zhouwei_cq@163.com).
Aiguo Patrick Hu and L. Huang is with the Department of Electrical and
Computer Engineering, University of Auckland, Auckland 1142, New
Zealand (e-mail: a.hu@auckland.ac.nz, lhua571@aucklanduni.ac.nz).