Researchers at Chalmers have developed an induction technology that enables battery charging without the help of humans or robotic arms. In addition, this technology is so mature that it can be presented to the industry immediately.
A new type of semiconductor based on silicon carbide. And the newly developed copper wire is as thin as a human hair. These are some of the factors that have suddenly made transmitting high power over the air more practical.
charging induction is new
Electric toothbrushes have been doing that for decades. In recent years, mobile phones and other portable electronic devices have adopted this technology. But given the high power required to charge electric vehicle batteries, previous wireless options seemed too complicated and ineffective.
However, inductive charging seems to be facing a breakthrough even for battery vehicles, especially when charging needs to be frequent and the environment is harsh. For example, for electric city ferries.
Charging without a human or robotic arm
This means that electric ferries that regularly ply the city waterways found in Gothenburg and Stockholm will not need the help of humans or robotic arms to recharge their batteries. The same applies to city buses and driverless electric vehicles used in industry, mining and agriculture.
Yujing Liu, power professor in Chalmers’ Department of Electrical Engineering, has a particular focus on renewable energy conversion and the electrification of transportation systems.
“We can build a system into the wharf that charges the ferry at several stops as passengers board and disembark. This is probably the most obvious application,” says Yujing Liu.
“Even electric trucks of the future probably have potential applications. Rather, the motivation is that the charging cable will be very thick and heavy and will need to be charged at such high power that it becomes difficult to handle.”
New Possibilities Brought About by Material Development
According to Yujing Liu, the rapid development of a small number of components and materials in recent years has opened up new possibilities.
“A key factor has been the availability of high-power semiconductors based on silicon carbide, so-called SiC components. As power electronics products, these are only a few years old on the market. Higher voltages, higher temperatures and much higher switching frequencies can be used compared to the base component,” he says.
This is important. This is because it is the frequency of the magnetic field that sets the limit of the power that can be transferred between her two coils of a given size.
4 times higher frequency
“Previously, vehicle wireless charging systems used frequencies around 20 kHz, like a normal stovetop. They were bulky and didn’t transfer energy very efficiently. After that, the induction suddenly becomes attractive, ”explains Yujing Liu.
His research group is in close contact with the world’s leading SiC module manufacturers, two companies based in the United States and Germany, he adds.
“They lead to rapid product development towards even higher currents, voltages and effects. Every couple of years new, more durable versions are launched. These types of components are It is an important ‘enabler’ with a wide range of applications, such as electric vehicles, as well as inductive charging. “
Another recent technological breakthrough concerns copper wires in coils that respectively transmit and receive oscillating magnetic fields that form a real bridge for the flow of energy across an air gap. The goal here is to use the highest possible frequency.
“Then a coil looped with ordinary copper wire will not work. It will lead to very high losses at high frequencies,” says Yujing Liu.
Instead, the coil consists of a “copper rope” made up of up to 10,000 copper fibers, each only 70-100 micrometers thick. It’s like hair.
Such braids of so-called litz wires adapted to high currents and frequencies have also become commercially available in the last few years.
A third example that Yujing Liu highlights is a new type of capacitor used to add reactive power, which is a prerequisite for allowing the coil to build a sufficiently strong magnetic field.
Yujing Liu emphasizes that charging an electric vehicle involves several conversion steps between DC and AC and between different voltage levels.
“So even if you say you’ve achieved 98% efficiency from charging station DC to battery, that number may not mean much unless you carefully define what you’re measuring,” he says. I have given a reason.
“But we can also put it this way: Whether we use normal conductive charging or inductive charging, there will be losses. Efficiency means that inductive charging losses are almost as low as conductive charging systems, the difference is so small that in practice it is negligible, about 1-2%.”
numbers grab attention
He adds that the results published by his research group have received a lot of attention.
“We are probably among the best in the world in terms of efficiency in this power class between 150 kW and 500 kW.”
Yujing doesn’t believe inductive charging will eventually replace cable charging.
“I drive an electric car myself, and I don’t see inductive charging in the future. You can drive home, plug it in… no problem.”
Is wireless charging a more sustainable technology than charging normally?
– It shouldn’t be argued that the technology itself is more sustainable. But it could make it easier to electrify heavy vehicles, accelerating the phase-out of diesel-powered ferries and the like.
Facts about inductive charging
- Charging using induction means that current can be transferred over short distances without contacts or conductors, such as through air, water, or other non-metallic materials.
- The principle is the same used in induction cookers found in many kitchens. When a high-frequency alternating current is passed through a coil, an oscillating magnetic field is generated.
- But unlike cooking, where heat production is the key, inductive charging means that a second coil on board the vehicle captures the energy in a magnetic field and converts it back into alternating current, which is called rectification. You can charge the battery later.
- Heat generated in the process means that some of the transferred energy is lost. Therefore, minimizing heating as much as possible is an important goal of technological development.
Original: New technology makes wireless charging attractive for electric cars and ferries
Than: Chalmers Institute of Technology
