Page 25 - PEN eBook May 2022

DESIGN Design

COIL CONFIGURATIONS

A 3D view of two different two-
coil configurations is shown in

Figure 1. The conventional WPT coil
configuration, consisting of two
identical flat-spiral coils well aligned
and separated by approximately
zero distance, is shown in Figure 1a.
The presented interleaved helical
WPT (IH-WPT) configuration, shown
in Figure 1b, consists of a coil pair
with coaxial helical coils, with one

coil inserted inside the other, which
Maximizing the has a slightly larger diameter. The

two coils can be aligned easily and
Efficiency of WPT maintain alignment even under Figure 1: Different types of WPT two-coil configurations
vibration and shock, due to the small

Air-Core Two-Coil air gap between them. Finally, the
configuration obtained inserting a

flat-spiral coil inside another helical
System Configurations coil is shown in Figure 1c.

To provide a better comparison
By Stefano Lovati, technical writer for EEWeb and evaluation, all of these

configurations have been evaluated
Wireless power transfer (WPT) systems are becoming more and more popular, with significant with frequency below 1 MHz (30 kHz
applications in the consumer electronics, medical device, and electric-vehicle charging sectors. to 1 MHz) and for short-distance
Among the different aspects involved in the design of WPT systems, one of the most relevant values, using coils made with almost

regards the coil-coupling configuration, or architecture. For high-frequency resonant WPT systems, equal self-inductance and diameter
the two-coil and four-coil configurations (without ferrites) are commonly used. However, in the case values. To obtain the S-parameters,
of medium-frequency WPT systems, ferrites are used to improve the wireless-power–transmission an experimental setup based on a
efficiency in near-field wireless charging applications, with a consequent increase in the weight vector network analyzer (VNA) was
and cost of the solution. Finally, short-range closely coupled WPT systems are normally free of used (Figure 2).
ferrites, thus achieving a reduced cost and weight at the expense of a reasonably lower efficiency.
Coil design plays a fundamental role in WPT systems, as it affects several aspects, including system MODELING OF THE Figure 2: The VNA-based experimental setup

behavior, efficiency, misalignment tolerance, and bandwidth of operation frequencies. TWO-COIL WPS
SYSTEM

This article analyzes and evaluates different WPT coil configurations for short-range and closely Because the two-coil WPT configurations are normally designed and analyzed as a single-input
coupled WPT systems, focusing on the wireless-power–transmission efficiency and lightweight single-output system, their model can be reduced to a two-port network model. The lumped circuit
design to reduce the overall mass of the WPT system. Read the original article here. model is shown in Figure 3a, where V and Z are the voltage source and impedance, respectively,
S S

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