Wirelesses charging of
electric vehicles continue to be one of the most researched areas of wireless
power transfer. By reducing the reliance on fossil fuels, electric
vehicles provide a sustainable and environmentally safe means for fuelling our
vehicles well into the future.
What is Wireless EV
Charging?
The growing EV market stimulates
the demand for more convenient and reliable means to recharge the battery. WPT
(Wireless Power Transfer) technique requires no physical contact between
vehicle and charging device, therefore overcomes the inconvenience and hazards
caused by traditional conductive method.
The initial objective is
replacing conductive charging method by the novel WPT technology, while
maintaining a comparable power level and efficiency. The long-term goal is to
dynamically power the moving vehicles on road. This will lead to a much reduced
battery pack but extended driving range. Then, the main concerns of EV, namely
the high battery price and the range anxiety, will be addressed.
Why wireless
charging?
· Wireless charging allows self-driving EVs to
recharge autonomously.
· Wireless charging simplifies the use of electric
vehicles.
· Reduces range anxiety, promoting EV adoption.
· Unique selling point of EVs: no more refueling.
· Wireless charging is essential for future
automotive industry.
Types of EV Charging
Methods –
Conductive Charging
(Regular) - Its just
plug the electric vehicle into a 13A Standard socket with dedicated circuit and
independent protective device. It is easy and convenient, but takes a longer
charging time AC charging using level 1 or level 2, voltage at 110V, 220V ，4-10 hours per charge.
Charge at home or public space, need large installation of charge stations.
Conductive
Charging (Fast Charging) - Charging in 15 to 30 minutes. For an EV
with a 24kWh battery pack, charging in 15 minutes means 96kW. This is way over
the power available in private homes. Fast charging can degrade battery lifetime.
Battery
Swapping – This method does not charge the electric vehicles directly
but replace the depleted battery with a fully charged one. The batteries are
not owned by the users but are rented ata cost to users. Users go to charging
station to swap the batteries to full charged one. The time required is short
but the vehicle use must be designed for such purpose. Investment of battery
packs, standardization is difficult, swapping stations need a lot investment,
space and manpower; safety and reliability is of concern.
Inductive
Charging or Wireless Charging – No cable connection is required,
instead the energy is transferred between the charger and the Paddle inside the
vehicles inlet via a magnetic field generated by a high AC current.
History of
Wireless Power Transfer
1830’s: Faraday's law of
induction
1890’s: Tesla had a
dream to send energy wirelessly
1990’s: GM EV1 used an
Inductive charger in the 1990’s
2007: MIT demonstrated a
system that can transfer 60W of power over 2 m distance at very low efficiency
2010: Wireless/inductive
chargers are available: electronics, factories, medical
2012: Qualcomm, Delphi
(Witricity), Plugless Power, KAIST, etc. have developed EV wireless charger
prototypes
2014 : in-motion charging
demonstration
Inductive charging (also
known as wireless charging) uses
an electromagnetic field to transfer energy between two objects through
electromagnetic induction. This is usually done with a charging station. Energy is sent through an inductive coupling to
an electrical device, which can then use that energy to charge batteries or run
the device.
An inverter
converts the DC power into high frequency AC current or voltage. The operating frequency varies from tens of kilohertz to several megahertz. The key element
is a pair of magnetically coupled coils. In order to enhance the mutual inductance,
ferrite cores are used in one or both sides of the coils. Litz wires are
frequently used to lower the parasitic resistance and therefore high Q-factor.
The litz coil consists of many individually insulated thin conductor stands
wounded in a particular patterns to reduce both the skin and proximity effects.
However, for frequency higher than 1 MHz, (e.g. 13.56 MHz) litz wires are less
effective and rarely used. Copper conductor or hollow copper tube could be
alternative solutions.
Dynamic
wireless charging – Charging an electric vehicle while driving is the
ultimate deployment of WEVC technology. Dynamic Charging removes the need for
constant charging stops, when travelling long distances: in fact, journeys of
hundreds of miles/kilometers would be possible with Dynamic Charging.
Dynamic wireless
charging is gaining more ground, since it enables power exchange between the
vehicle and the grid while the vehicle is moving.
Wireless EVC Standards
In May, 2016, the
society of automotive engineers approved the J2954 standard for
wireless charging of electric vehicles. They claimed that this standard
truly is a game changer, that allows people to simply park your car and walk
away, and your car will start charging automatically.
Qi (pronounced CHEE,
from the Chinese word "natural energy"), is an open interface standard developed
by the Wireless Power
Consortium for inductive charging over
distances of up to 4 cm (1.6 inches). The system uses a charging pad and a
compatible device, which is placed on top of the pad, charging via resonant inductive
coupling.
Leading Wireless
EVC Manufacture Company –
· Delta Electronics Ltd.
· Qualcomm Halo
· ABB Ltd.
· And many more …
Wireless EVC
Advantages
Protected connections
– No corrosion when the
electronics are all enclosed, away from water or oxygen in the atmosphere. Less
risk of electrical faults such as short circuit due to insulation failure,
especially where connections are made or broken frequently.
Low infection risk – For embedded medical devices, transmission of
power via a magnetic field passing through the skin avoids the infection risks
associated with wires penetrating the skin.
Durability – Without the need to constantly plug and unplug
the device, there is significantly less wear and tear on the socket of the
device and the attaching cable. Increased convenience and aesthetic quality –
No need for cables.
Wireless EVC
Disadvantages
Slower charging – Due to the lower efficiency, devices take
longer to charge when supplied power is the same amount.
More expensive – Inductive charging also requires drive
electronics and coils in both device and charger, increasing the complexity and
cost of manufacturing.
Inconvenience - When a mobile device is connected to a cable,
it can be moved around (albeit in a limited range) and operated while charging.
In most implementations of inductive charging, the mobile device must be left
on a pad to charge, and thus can't be moved around or easily operated while
charging.
Conclusion
From luxury electric
sedans to everyday commuter cars, the discussion about wireless charging is
popping up everywhere. Industry and customers agree that the hassle of cords is
one of the barriers slowing EV adoption. Wireless charging helps electric
vehicles surpass the convenience of gas cars. Even the most far-out ideas
around wireless charging may become reality sooner than most expect.
*** All data are gathered form trusted source/websites.
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