IEEE Circuits and Systems Magazine - Q3 2019 - 24

the low susceptibility made it very popular for many
different applications.
In the late 1970s academic interest in IPT for charging electric vehicles (EV) in motion on special lanes
was started, especially by Bolger et. al. [5], [6]. This research in wireless charging and dynamic powering has
been advanced and is still being investigated in [7]-[9],
has been expanded for e-bikes [10] and for mobile consumers on given tracks in the industry [11]. IPT also has
become an established standard for charging parked
EVs [12]-[17].
Another wide range of applications from the recent
past is wireless charged consumer electronics [18] with
several standards, e.g. the Qi standard [19], [20].
In industrial applications IPT is able to fully utilize its
advantages of not requiring cables and as alternative solution to slip ring systems for rotating applications [21]-[23].
IPT is used also in other applications like power supply in aircraft [24], a contactless connector [25], a fridge
display [26], underwater power delivery [27], [28], maglev application [29], mining solution [30], stage lighting [31], [32] or security camera [33].
For most applications an absolutely reliable data
channel between the primary and secondary side of the
IPT system is essential for a safe operation. For the regulation and control of the power transfer, information
from the secondary side (e.g. output voltage and current)
is required and needs to be transferred to the control
unit on the primary side [34] or has to be estimated [15].
The common way to communicate is to use a radio frequency (RF) link to transfer this data, e.g. Bluetooth [35]. Also the IEEE 802.15.4 radio standard is used
like in  [36] (ZigBee) or  [34]. The disadvantage of a RF
link are interferences due to the IPT system and, especially for areas with high density of IPT, the compatibility with other systems. Therefore, a locally limited data
link within the system would be preferable which also
increases the safety against relay attacks.
Several methods, which modulate the power transfer
signal for communication, are presented. Load modulation is used to transfer data from the load to supplying
side  [3],  [19]. If communication in the opposite direction is desired, an additional concept such as modulating the inverter's switching frequency with frequency
shift keying (FSK) [22] or amplitude shift keying (ASK)
of the inverter voltage  [37] is needed. This however is
a severe intrusion in the IPT system and can lower the
efficiency significantly. Furthermore, communication is

only possible if power is transferred and it is limited to
the switching characteristic of the IPT system.
Other approaches add an additional data coil for the
communication with multiple carrier frequencies as published in [26], [38]-[40]. These methods do not affect the
power transfer but suffer from magnetic influences due
to a strong power signal which lowers the signal-to-noise
ratio (SNR) of the communication channel. To avoid this,
the coils have to be oriented specifically in order to prevent interaction of the magnetic fields. This however
makes the system very vulnerable to misalignment.
A promising approach is overlapping the power signal with a modulated data signal with a higher carrier
frequency like published in  [22], [41]-[44]. Admittedly
this method suffers from the high power level of the harmonics due to the IPT square signal and a high noise
floor because of the hard switching process. The higher
the power of the IPT system the more this effect intensifies.  [22] and  [41] only communicate during the nonswitching period of the inverter in order to minimize
those aforementioned problems. Contrarily,  [42]-[44]
presented methods which can continuously send data
with rates of 19-20 kbit/s.
In order to eliminate all these aforementioned problems, a method using a carrier frequency lower than the
switching frequency of the inverter has been successfully introduced in [25], [45], [46].
In this article this method will be further improved
with a joint system design with separate carrier frequencies for power and data transfer in one common inductive power link. This has the advantages that no extra
coils are needed, the power and data transfer channel is
independent from each other and the IPT system does
not have to be changed for simultaneous data transfer.
To reach maximum possible performance for both subsystems, the system is designed jointly.
II. Joint System Specifications
The goal of this article is to design a joint IPT system
which can transfer power up to 20 W at an input voltage
of approximately 24 V and can simultaneously communicate bidirectionally in all operating conditions, even if
the power electronic is switched off. To achieve this, the
power and communication concept as well as mutual interferences must be considered in a holistic approach. If
deviating power and data requirements are wanted, the
presented design parameters can be adapted to the specific use case.

M. Trautmann and B. Sanftl were with the Institute for Electronics Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, Cauerstr. 9, 91058
Erlangen, Germany, e-mail: martin.trautmann@fau.de. R. Weigel is with the Institute for Electronics Engineering, Friedrich-Alexander-Universität
Erlangen-Nürnberg, Cauerstr. 9, 91058 Erlangen. A. Koelpin is with the Chair for Electronics and Sensor Systems, Brandenburg University of Technology,
Siemens-Halske-Ring 14, 03046 Cottbus, Germany.

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