IEEE Electrification Magazine - March 2020 - 43

will be operated at a reduced frequency, possibly in the
order of 20 kHz, as used by the first high-power systems
demonstrated for buses and trams.
The scaled-down inductive road testbed, including one
onboard coil and two different roadside coils, was
designed and built; the parameters are reported in Table 2.
Note that the nominal charging power and size of the coils
are scaled to the 1:14 ratio of the truck model, as discussed
in the previous section. On the other hand, the model's
operating frequency was chosen rather arbitrarily, since
following the ideal scaling law (196:1) would have resulted
in a very high value that would have presented significant
practical challenges without giving much additional
insight. A picture of the coil mounted on the small-scale
truck model appears in Figure 3(a).
The intention of having two road-coil designs was to
illustrate the flexibility of the concept, showing the
interoperability of different designs, as long as they are
tuned to the same resonant frequency. Thus, the further
intention of the small-scale demonstration platform is to
prove that designs based on coils with different shapes

and even with different flux patterns can be investigated.
In the presented system, one coil was designed with a
focus on high efficiency (roadside coil 1), using more copper for the winding and high-grade ferrites. The other coil
(roadside coil 2) was designed for a low cost, resulting in a
lower quality factor and consequently a lower transfer
efficiency. A picture of the two coils mounted side by side
as a two-coil dynamic-charging lane for the small-scale
truck model is given as Figure 3(b).

Power-Conversion Topology and Control
Due to the considerable air-gap distance between the
transmitting and receiving coils, the system for inductive
power transfer can be regarded as a poorly coupled transformer with a very high leakage flux that causes a high
consumption of reactive power compared to the active
power that can be transferred between the coils. Thus, a
high efficiency and reasonable rating of the power-electronic converters can only be achieved by using resonant
networks with capacitive compensation at both sides of
the charging system for supplying the reactive-power

TABLE 2. The coil parameters
for the small-scale truck model.
Parameter

Specification

Nominal power, P0

75 W

Nominal I/O voltages, Vdc,in, Vdc,out

12 V, 7.4 V

Nominal operating frequency

75 kHz

Vehicle-Side Coil
Planar dimensions

100 × 100 mm

Self-inductance (above roadside coil), L2

7.9 µH

Quality factor, Q (at 75 kHz)

163
(a)

Roadside Coil 1
Planar dimensions

570 × 100 mm

Equivalent length in full scale

8m

Self-inductance (with no pickup), L1

37 µH

Quality factor, Q (at 75 kHz)

293

Roadside Coil 2
Planar dimensions

440 × 100 mm

Equivalent length in full scale

6.2 m

Self-inductance (with no pickup), L1

31 µH

Quality factor, Q (at 75 kHz)

143
(b)

Coupling Conditions
Air-gap distance

22 mm

Figure 3. Coils designed for the small-scale demonstration

Coupling factor, k (centered, maximum
coupling)

0.16, 0.18

- latform, with (a) the vehicle-side coil and (b) the two road-side
p
coils mounted side by side in a short road section for dynamic
-wireless charging.

	

IEEE Elec trific ation Magazine / MARCH 2 0 2 0

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IEEE Electrification Magazine - March 2020

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