IEEE Electrification Magazine - June 2020 - 54

The limitations of the fast-charging station are 1)
although the charging power can reach 200 kW, the charging time is still relatively long, especially when more vehicles are waiting at peak hours, 2) it requires a large battery
size, which increases the vehicle cost, 3) the cost of a fastcharging station is still very high. It requires a few megawatts of pulse power from the power grid, which is
challenging to achieve, and 4) the traffic condition of the
charging station is difficult to manage; therefore, it is necessary to develop dynamic charging technology.
The following are the major benefits of dynamic charging technology:
xx
Increase driving range: Because vehicles are continuously charged in moving status, the mileage-anxiety
concern is completely eliminated, which cannot be
achieved by any other existing technology and infrastructure. As a result, the adoption of green transportation is expected to increase dramatically.
xx
Improve transportation efficiency: Dynamic charging
overcomes the limitation of the slow-charging rate. The
extra transportation time caused by using the charging
station and the waiting time during charging are both
saved. During rush hour especially, it contributes to
alleviating traffic congestion. The construction of fastcharging stations along the highway is reduced, and
the possible waiting line around the stations is, therefore, lessened.

xx
Improve transportation safety: Because the vehicles

could be charged more frequently, the size of the onboard battery pack is significantly reduced, resulting
in less risk of explosion in accident scenarios. Furthermore, electric vehicles are conveniently connected
and share traffic information, which contributes to
avoiding potential accidents.
xx
Alleviate the demand response from power grid: The
dynamic charging system is built along the roadway
and the load is evenly distributed. Compared to a fastcharging station, the transient power requirement
from the power system is reduced. It is convenient to
have distributed energy resources along the roadway
to reduce power demand from the grid.
The existing dynamic wireless power-transfer technology is mainly based on the inductive power transfer method presented in Figure 2. A long coil is embedded
underneath the ground and works as the transmitter
track. There is a relatively high current circulating in the
transmitter to generate magnetic fields. However, the
induced eddy-current loss may cause a temperature rise
and fire hazards. Moreover, the conduction loss is significant when the coil size increases to 10 or even 100 s of
meters for dynamic charging. In addition, the Litz wire
and ferrites in coils are very expensive and fragile. When
vehicles move on the top of the roadway, the coils cannot
last long, which will reduce the system's lifetime and
affect its maintenance.

TABLE 1. A comparison of stationary and

Structure of Dynamic Capacitive
Wireless Charging

IEEE Electrification Magazine - June 2020

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