Magnetism and electricity: A brief analysis of wireless charging technology for power CR2032 battery

Wireless dynamic charging is still in the research stage and is still a long way from being widely popularized. However, technology is always developing. Believe in the power of technology, the problem of charging will always be solved. It is definitely not a foolish dream for electric vehicles to charge while driving.

Charging is like a bug for electric vehicles. If one day, electric vehicles get rid of the constraints of charging piles and don’t have to look for charging piles everywhere, how great it would be to charge more conveniently than refueling.

Seeing this, everyone should understand the topic to be discussed today, wireless charging. However, unlike wireless charging in parking spaces, what we are going to discuss today is the technology of charging while driving. Of course, it also has a very academic name, called electric vehicle dynamic charging (DEVC) technology.

Imagine that electric vehicles do not need to be charged deliberately, and can be charged on the road every day, which brings many benefits. First of all, it can "reduce the burden" of the battery, because the car can be charged anytime and anywhere, so large-capacity batteries are not so necessary, and the vehicle's load will also decrease accordingly.

Secondly, there is no need to wait for charging. Now, charging electric vehicles is still not as convenient as refueling gasoline vehicles, while wireless charging can be charged while driving, reducing time costs. Finally, the range problem is solved. The range of electric vehicles is wirelessly extended, and the range anxiety problem does not exist.

Sounds like a fantasy? In fact, theoretically, it is not difficult to achieve. Let's first understand its principle.

1. What is wireless charging?

Let's start with wireless charging. We know that wireless charging relies on current and magnetic field. Electricity and magnetism are a pair of love-hate CPs that often do things together.

In 1819, Danish scientist Oster observed that if there is current on a section of wire, a magnetic field will appear around it. Later, people found that if the wire is surrounded by a ring or even a coil, the magnetic field will 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 close to a coil without current, an induced current will appear on the coil, which is called electromagnetic induction.

So how can we make electricity and magnetism work and output current to us stably?

We need two coils. If we power one coil, there will be a magnetic field around it. Then we move the other coil closer, and there will be current in this coil. The current is guided into the battery, and wireless charging can be completed.

Applied to the automotive field, this is electromagnetic induction wireless charging.

We pass alternating current to the coil on the ground. As the current changes in size and direction, the strength and direction of the magnetic field around the coil also change continuously, forming an alternating magnetic field. At this time, the coil on the chassis of the vehicle is in a constantly changing magnetic field, and an alternating current will appear inside the coil. After rectification through a series of circuits, the battery is charged.

2. Wireless charging forced to have obsessive-compulsive disorder

Electromagnetic induction wireless charging is a technology that major automobile companies prefer to use in the early stage of wireless charging research.

There will be something that looks like a mat on the parking space. In fact, it is a primary coil used to generate a magnetic field. The chassis of a vehicle that can be used for wireless charging will also have a coil, which we call a secondary coil, used to generate current.

However, there is a big disadvantage of electromagnetic induction wireless charging, which is distance. In order for this technology to generate current, the two coils must be "perfectly" opposite to each other. Once there is a deviation, the current will not appear.

Therefore, such technology often needs to be combined with precise automatic parking technology to make the vehicle park right above the wireless charging pad.

It sounds very troublesome, right? This is the rhythm of making everyone a Virgo with obsessive-compulsive disorder.

So scientists studied another wireless charging technology, which is magnetic field resonance wireless charging. We know that when two objects use the same vibration frequency, or resonate at a specific frequency, they can exchange each other's energy.

Magnetic field resonance means that the primary coil has a magnetic field that vibrates at a fixed frequency, namely the resonant magnetic field, and then the vibration frequency of the secondary coil magnetic field is the same as it, resonance occurs, and finally energy transfer is achieved.

In 2007, the research team of MIT successfully lit a 60W light bulb 2m away through an electromagnetic resonator.

In the automotive field, Toyota conducted an experiment 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 the 85kHz power transmission efficiency that is internationally agreed upon, which is about 80%.

In this verification experiment, the distance between the resonant magnetic field on the ground and the secondary coil at the bottom of the vehicle is about 15cm. The maximum allowable range of horizontal misalignment is the width of a tire (about 20cm).

Qualcomm has also launched a wireless charging system called Halo, but it also stays at static wireless charging.

The magnetic resonance effect is used to achieve energy transmission between the ground charging pad and the electric vehicle charging plate. This charging system has a power of up to 20kW, and it takes about 5 hours to fully charge the 85kWh TSLAMODELSP85 battery pack.

3. Make electric vehicles move

If the charging pad or the resonant magnetic field is placed on the road, the vehicle can be charged while running, and say goodbye to the charging pile.

In May of this year, Qualcomm completed a dynamic wireless charging road test in Paris using a Renault all-electric Kangoo van.

Two electric cars 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.

The 100m long road test built by Qualcomm contains 4 energy supply units, each of which is responsible for the power supply of 25m road. At the same time, each 25m long energy segment has 14 submodules, including coils and energy conversion circuits.

As for the cost issue, a study by Renault, Electricité de France and the French Northern Motorway Company pointed out that the cost of building a dynamic charging road is 4 million euros/km (two-lane), which can be said to be quite expensive.

Such a "precious" road seems to be popularized only on bus lanes first. In South Korea, the Korea Advanced Institute of Science and Technology (KAIST) built a 12km long dynamic charging road at the railway 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. Well-known companies include ZTE, which has already started testing wireless charging demonstration lines in Chongqing, Hubei and other places.

Wireless dynamic charging is still in the research stage and is still a long way from being widely popularized. Just thinking about it, there are a lot of problems that have not been solved, such as whether the compatibility of vehicles is consistent, whether the road is open or closed, and whether the current of the road can load multiple vehicles for charging? In addition, there is road monitoring and maintenance. These are all obstacles to wireless dynamic charging, but technology is always developing. I believe that with the power of technology, the problem of charging will always be solved. It is definitely not a foolish dream to charge an electric car while driving.

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