01-10-2012, 10:53 AM
Design and Implementation of a Rectangular-Type Contactless Transformer
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Abstract
In this paper, a rectangular contactless transformer
is proposed to be used in a contactless power supply system. The
proposed rectangular contactless transformer maintains a high
coupling coefficient even when it has a relatively large air gap.
The characteristics of the proposed transformer are compared to
a transformer using a general EE core with a variable air gap. The
proposed system is verified through simulation and experimental
results. The experimental results demonstrate that the efficiency
of the contactless power transmission system using a contactless
transformer based on a rectangular core is over 20% greater than
the system based on the EE core.
INTRODUCTION
A contactless power conversion system accomplishes power
transfer by using the magnetic coupling of the transformer
without any mechanical contact. Various applications of the
contactless power conversion system have been studied [1]–
[3]. However, since the two windings of the transformer are
physically separated by an air gap, this air gap produces a low
coupling coefficient and high leakage inductance, which, in
turn, results in a poor power conversion efficiency [4], [5].
The challenge is, therefore, to increase the efficiency in spite
of the large air gap of the contactless transformer. In order
to decrease the effect of the large leakage inductance in a
contactless transformer and to thereby increase the efficiency,
various types of resonant converters have been studied and
applied [6]. However, it is still very important to study the
contactless transformer structure itself, one that maintains a
high coupling coefficient even with a large air gap.
Analysis of the Contactless Transformer
By using Maxwell 3-D software, the flux flows and the flux
distribution of the EE core and rectangular core are compared.
The contactless transformer parameters for the designed and
implemented cores are analyzed. Fig. 3(a) and (b) shows the
magnetic flux distribution on the EE core surface and rectangular
core surface, respectively. We see that the magnetic flux
density in the rectangular core center leg is higher than that of
the EE core.
Tables III and IV show the measured parameters of the
contactless transformers using an EE core and a rectangular
core, respectively. The transformer parameters are measured for
the designed and implemented contactless transformers with an
air gap variation between 1 and 10 mm.
CONCLUSION
In this paper, a contactless power transmission system using
a contactless transformer based on a rectangular core has been
proposed. In order to verify the proposed system, the system
has been designed and implemented. The experimental results
have demonstrated that the efficiency and output power of
the contactless system based on the rectangular core with a
10-mm air gap are higher than that of the system based on an
EE core with a 1-mm air gap. Furthermore, the efficiency of
the contactless power transmission system using a contactless
transformer based on the rectangular core is over 20% higher
than the system based on the EE core over the whole range of
air gaps between 1 and 10 mm.