IEEE Electrification Magazine - June 2020 - 59

Position 1

Position 2

Vehicle 1
Ground E

Transmitter
Power Supply

Position 3
Vehicle 3

Vehicle 2

Compensation
Inverter

Figure 12. A long-transmitter track with multiple vehicles at different positions.

Considering the
vehicle's weight on
pavement, metal
plates are much
more reliable than
coils made by Litz
wire and ferrite.

Challenges in Dynamic CPT Systems
In practical applications, there are three major challenges
in a long-track dynamic CPT system:
1) The self-inductance of the transmitter plate affects
the power-transfer process at different positions.
It is possible to have a transmitter length of 10 s of meters.
The connection position of the primary compensation circuit
affects the current-flowing path on the transmitter track. It is
better to connect in the middle of the track to shorten the
path of the current. There could be multiple receivers moving
along the transmitter track. The positions of electric vehicles
are used to illustrate the influence of the transmitter trackparasitic inductance, as depicted in Figure 12.
Receiver 2 is placed in the middle of the transmitter
track, just on top of the compensation circuit connection.
The other receivers are placed at the edge of the transmitter, and the currents must travel a long distance to reach
the receiver. The FEM simulation indicates that the selfinductance can reach 10 s of μH, which affects the circuit
resonance and reduces power. When the switching frequency is in the MHz range, the influence of plate selfinductance can be much more significant. It is, therefore,
meaningful to study the self-inductance of the transmitter
plate to reduce its side effects.

2) At a very high frequency, the radiated loss from the transmitter
plate to the free space can be significantly increased, which affects
system efficiency and safety.
In a CPT system, increasing the frequency fsw contributes to increasing
the system power and reducing the
size of the passive component. With
the development of modern widebandgap semiconductor materials,
the switching frequency of a highpower device is expected to reach as
high as 100 MHz. When fsw increases,
the wavelength m of the generated electromagnetic wave is
reduced. According to c = m·fsw, where c is the speed of
light, the quarter-wavelength m/4 is calculated, as depicted in Figure 13. It demonstrates that when the switching
frequency is as high as 1 MHz, the quarter-wavelength is
m/4 = 75 m. If the switching frequency increases to
100 MHz, the quarter wavelength decreases to 0.75 m. If
the transmitter track length is close to or larger than m/4,
the transmitter will behave as an antenna to radiate a
large amount of system power to the free space. In this
case, the system power and efficiency will be significantly
reduced. Meanwhile, the radiated power is also a critical
safety issue to the general public. Based on this concern,
the working frequency of a dynamic CPT system should
be within the MHz range.

80
60
λ /4 (m)

the traveling time can be fully utilized and transportation efficiency is
also improved.
On the high-speed electric roadway,
it is not necessary to cover all the
pavement with the charging system.
For example, the segmented transmitter structure can be adopted, and each
track length is set at 50 m. When the
vehicle speed is 60 mi/h, the effective
charging time is roughly 1.86 s. The
working frequency of the CPT system
is in the MHz range, and the transient
response time of the high-frequency
resonant circuit is in the μs range. Therefore, there is sufficient time for the dynamic charging system to respond to
high-traveling rates of speed.

40
20
0
100

101
Switching Frequency fsw (MHz)

102

Figure 13. The relationship between switching frequency fsw and
quarter-wavelength m/4 of the electromagnetic wave.

IEEE Elec trific ation Magazine / J UNE 2 0 2 0

IEEE Electrification Magazine - June 2020

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