Wireless dynamic charging is still in a state of research and is still a
long way from being widely popularized. However, technology is always
developing. I believe in the power of technology, the charging problem will
always be solved. Charging an electric car while driving is definitely not a
pipe dream.
Charging is like a bug for electric cars. It would be great if one day,
electric cars get rid of the constraints of charging piles and don't have to
look for charging piles everywhere. Charging is more convenient than
refueling.
After seeing this, everyone should understand the topic we are going to
discuss today, wireless charging. But unlike wireless charging in a parking
space, what we are going to discuss today is charging technology while driving.
Of course, it also has a very academic name called dynamic electric vehicle
charging (DEVC) technology.
Imagine that electric cars don’t need to be charged deliberately and can be
charged while driving on the road every day, which brings many benefits. First
of all, the load on the battery can be reduced, because the car can be charged
anytime and anywhere, so large-capacity batteries are no longer necessary, and
the load of the vehicle is also reduced.
Secondly, there is no need to wait for charging. Nowadays, charging of
electric vehicles is not as convenient as refueling of gasoline vehicles.
However, wireless charging can charge while driving, reducing time and cost.
Finally, the cruising range problem is solved. The cruising range of electric
vehicles is wirelessly extended, and the problem of range anxiety no longer
exists.
Sounds like a fantasy? In fact, theoretically speaking, it is not difficult
to implement. Let’s first understand its principle.
1. What is wireless charging?
Let’s start with wireless charging. We know that wireless charging relies
on electric current and magnetic field. Electricity and magnetism, a pair of
lovers who love each other, often do things together.
In 1819, Danish scientist Oersted observed that if a current flows through
a wire, a magnetic field will be generated around it. Later, people discovered
that the magnetic field generated by surrounding the wires into a ring or even a
coil would be stronger and more concentrated. This is called the current
magnetic effect.
In 1831, Faraday discovered that if a magnet or other magnetic field source
is brought close to a coil with no current, an induced current will be generated
in the coil. This is called electromagnetic induction.
So how do we make electricity and magnetism interact and stably output
current to us?
We need two coils. If one coil is energized, then there will be a magnetic
field around the coil; then we move the other coil close to it, then there will
be current in the coil. When the current is directed into the battery, wireless
charging can be completed.
Applied to the automotive field, this is electromagnetic induction wireless
charging.
We apply alternating current to the coil on the ground. As the magnitude
and direction of the current change, the strength and direction of the magnetic
field around the coil also continue to change, forming an interactive magnetic
field. At this time, the coil of the vehicle chassis is in a constantly changing
magnetic field, and an interactive current is generated inside the coil, which
is rectified through a series of circuits to charge the battery.
2. Wireless charging forced out of obsessive-compulsive disorder
Electromagnetic induction wireless charging is a technology that major
automobile companies prefer to adopt in the early stages of research on wireless
charging.
There will be something that looks like a mat in the parking space, but it
is actually a primary coil used to generate a magnetic field. Vehicle chassis
that can be used for wireless charging will also have a coil, called a secondary
coil, to generate electrical current.
However, electromagnetic induction wireless charging has a big drawback,
and that is distance. In order for this technology to generate current, the two
coils must be exactly opposite each other. Once deviation occurs, the current
will not be generated.
Therefore, such technology often needs to be paired with precise automatic
parking technology to make the vehicle park just above the wireless charging
pad.
It sounds very troublesome, right? This is to make everyone practice the
rhythm of Virgo plus obsessive-compulsive disorder.
Therefore, scientists are studying another wireless charging technology,
which is magnetic field resonance wireless charging. We know that when two
objects vibrate at the same frequency, or resonate at a specific frequency, they
can exchange energy with each other.
Magnetic field resonance means that the primary coil generates a magnetic
field that vibrates at a fixed frequency, that is, a resonant magnetic field,
and then the vibration frequency of the secondary coil's magnetic field is the
same as it, creating resonance and ultimately achieving energy transfer.
In 2007, a research team at MIT successfully lit a 60W light bulb 2m away
through an electromagnetic resonator.
In the automotive field, Toyota conducted experiments in 2012, adding a
secondary coil that can vibrate at a certain frequency to a plug-in hybrid
Prius. There is a resonant magnetic field on the parking space. When they all
vibrate at the same frequency, the secondary coil can convert the current of the
resonant magnetic field.
The output power of this wireless power supply system is 2kW. The frequency
band used is 85kHz, which is internationally recognized, and the power
transmission efficiency is about 80%.
In this verification experiment, the distance between the ground's resonant
magnetic field and the secondary coil at the bottom of the vehicle was about
15cm. The maximum allowable range of horizontal misalignment is the width of one
tire (about 20cm).
Qualcomm has also launched a wireless charging system called Halo, but it
also stayed at static wireless charging.
The magnetic resonance effect is used to realize energy transmission
between the ground charging pad and the electric vehicle charging plate. The
power of this charging system can reach 20kW, and it takes about 5 hours to
fully charge the 85kWh Tesla MODEL S P85 battery pack.
3. Let electric cars move
If a charging pad or a resonant magnetic field is placed on the road, the
vehicle can be charged while running and say goodbye to charging piles.
In May this year, Qualcomm completed a dynamic wireless charging road test
in Paris using a Renault all-electric Kangoo van.
Two electric vehicles drove on this 100m-long road at different speeds and
completed charging at the same time. During the test, the speed of the Kango
test car reached 100km/h, and the maximum charging power could reach 20kW.
This 100m-long road test constructed by Qualcomm contains 4 energy supply
units, each unit is responsible for the power supply of 25m of road. At the same
time, each 25m long energy section has 14 sub-modules, including coils and
energy conversion circuits.
As for the cost issue, a study by Renault, EDF and Northern France Highways
Company pointed out that the cost of building dynamic charging roads is 4
million euros/km (dual lane), which can be said to be quite expensive.
It seems that such expensive roads can only be popularized on bus routes
first. In South Korea, the Korea Advanced Institute of Science and Technology
(KAIST) has built a 12km long dynamic charging road at the train station in Gumi
City in the south. The electric buses running on it use magnetic field resonance
to achieve wireless charging.
After talking about foreign countries, our country’s research on wireless
dynamic charging is not lagging behind. The more well-known one is ZTE, which
has already started testing wireless charging demonstration lines in Chongqing,
Hubei and other places.
Wireless dynamic charging is still in a state of research and is still a
long way from being widely popularized. Just thinking about it, there are a lot
of problems that have not yet been solved, such as whether the compatibility of
vehicles is consistent, whether the road is open or closed, and whether the
current on the road can load multiple vehicles for charging? There are also road
monitoring and maintenance. These are all obstacles to wireless dynamic
charging, but technology is always developing. I believe in the power of
technology, the charging problem will always be solved. Charging an electric car
while driving is definitely not a pipe dream.
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