from Tesla’s dream to the technological reality of the next few years.
Can you imagine a world without cables? Something like this is what Nikola Tesla envisioned since the end of the s. XIX with his experiments based on electrostatic induction. With these experiments he surprised crowds by showing, among other things, how he could illuminate bulbs without plugging them in. The development of the Wardenclyffe tower was the maximum exponent of its strong commitment to wireless systems, although in less than a year that same project was one of the causes that led to its ruin.
Years passed and the idea was forgotten until it was rescued more than a century later, just a decade ago, by Marin Soljiacic in her research associated with MIT. From this moment on, the applications of this technology have exploded and, of course, has also reached the charging of electric vehicles. Let us know in detail how this technology works and what it will mean for the electric car sector.
Wireless electricity: Faraday and resonance
Let us understand, first of all, the principle of operation. To do this, it will be necessary to turn to one of the main references in history in the study of electricity and magnetism: Michael Faraday.
In his law of electromagnetic induction, published in 1831, he described that a conductive medium, when traversed by a variable magnetic field, will have induced a potential difference that will lead to an electric current. In the same way, the phenomenon occurs in the opposite case: a current flowing through a conductor will have a magnetic field associated with it.
Now, what use is this to us? What does it have to do with wireless electricity? According to what we have seen, if we form a winding by making many turns with a conductor and we make electric current pass through it, we will be generating a magnetic field that will be greater the more turns we have created. That device is an electromagnet.
And what if we pit it against another winding that is connected to a light bulb? Well, each of the turns of this new winding will perceive a potential difference due to the magnetic field. That potential difference will give rise to a current and … Eureka! There was light.
This was one of the first experiments by Soljacic, the Croatian researcher at MIT, and the starting gun for a whole new technology that has already reached various sectors of the industry. And as, the electric vehicle could not be lacking in its many applications either.
By installing an emitter winding, which will receive energy from the electrical network, it is intended transmit electricity through magnetic fields to the receiver winding located inside the car so that the induced current recharges its batteries. And, although it seems fiction, the truth is that there are already facilities in operation and several innovation projects whose main objective is to standardize technology.
At this point, it is logical that a problem arises: how is it possible that energy losses do not make this technology unviable? If instead of being conducted by a wire the current has to be induced by a magnetic field, it is to be assumed that there will be less efficiency in the transfer of energy. However, not everything that is gold glitters and in this case we could not be further from the truth. Really efficiency losses are very small and this is achieved thanks to magnetic resonance imaging.
Just as when a soprano manages to break the classic glass by synchronizing the frequency of her singing with the resonance frequency of the crystal, the same effect can be produced with the electromagnetic field. The receiving coil, due to its constructive characteristics, will have a specific resonance frequency. If it is made to coincide with the frequency of the alternating current that will generate the magnetic field, we will be able to maximize the efficiency of energy transfer.
To talk about figures, we have contacted the CIRCE Foundation, from where several cutting-edge investigations have been carried out in the field of wireless recharging of vehicles. We were attended there by Carlos Pueyo, Director of the Network Systems Integration Area. “Our designs reach transfer efficiency levels above 96%. In real applications, counting on the misalignment of the coils or the change in height between primary and secondary, this performance could drop to 90%. “Undoubtedly, figures that invite us to imagine a world in which these systems become popular.
Wireless vehicle charging is near
The application to electric vehicles of the so-called witricity is already presenting numerous advances at great speed. So much so that there is already various prototypes in operation in different countries Europeans, including ours. Some of the most cutting-edge projects in terms of innovation in wireless recharging of vehicles have been developed in Spain in recent years. And the CIRCE Foundation has been in several of them from its main headquarters in Zaragoza.
“The advantages it presents compared to conductive charging are fundamentally centered on its flexibility, usability and the protection of the equipment against vandalism, as it is underground”, emphasizes Pueyo. This aspect also reduces the visual impact of conductive charging systems. To be sure, there are plenty of reasons to think that inductive charging has a high potential. “There are already several examples in Europe and we trust that in the next 5 years we will see facilities in the main cities of the world”.
One of the first projects developed in this area was Unplugged, made up of more than 17 partners with the aim of creating a flexible inductive charging station. “A modular system was proposed to power 25 kW or 50 kW systems depending on the type of vehicle that accesses the charging system. This facilitates the use of the infrastructure by a greater number of vehicles”, Pueyo comments.
But, although Unplugged ended last year 2015, since the Aragonese foundation they continue to research and work in the wireless electricity sector and its applications. CIRCE’s Technological Expert for Network Studies and Smart Grids, Hans Bludszuweit, has given us a vision of the next steps that this technology will take.
“First, low-power domestic systems (slow charging), which already have commercial solutions, will be extended. A little later there will be 50 kW and more systems for recharging in public transport (buses and taxis).” Along these lines, Carlos Pueyo points out that wireless systems “make it possible to carry out Opportunity loads that should otherwise involve wiring of a hose. This makes it easier to reduce the kWh of storage shipped in the vehicles, which is a very relevant part of their cost. “
Although for this to be effective it is necessary to increase the speed of the load. Last Thursday, October 26, a milestone was achieved within CIRCE: triple induction power transmission capacity reaching up to 300 kW. Thus, we arrive at the order of magnitude of ultrafast charging systems that allow a reduced recharge time by up to 60% relative to currently available systems.
But this field of work is not limited to research centers. Also companies are making a strong bet on wireless technology for recharging vehicles, as shown by its strong presence in all the innovation projects mentioned. In addition, the main electric vehicle manufacturers are developing their own systems of recharging by witricity to be able to incorporate this technology to their models.
This decade has been a key one in the boom in wireless technology. Car giants such as Audi have worked in recent years to incorporate charging coils in their vehicles and already on their website they announce their next addition to the long-awaited e-Tron. Also companies such as Daimler or Nissan are working on the incorporation of this recharging system to their models, preparing for a fairly close reality.
In addition, the Japanese company collaborates closely with the startup WiTricity (founded by the aforementioned Marin Soljacic) for the development of a standardization plan for the international protocol SAE J2954, which considers this type of load for vehicles.
In search of price reduction
Undoubtedly, a multitude of applications are foreseen for this type of system in the future. At the domestic level, there are already slow-loading device applications, although their presence will increase. Also in the industrial field, they are an advantage by providing robots with greater autonomy. Returning to the electric mobility sector, a high potential for its application in the recharge of public transport services and shared autonomous cars. This would be, perhaps, one of the future applications in which wireless charging could contribute the most.
To make this a reality, research is currently being carried out in the recharging moving vehicles. Along these lines, the telecommunications company Qualcomm installed in Versailles an inductive road demonstrator prototype in which they used the same concept: a rail with windings under the asphalt that induce current in the internal windings of the vehicles and recharge their batteries. The objective was that the balance between the consumption of the vehicle and the recharge they received minimize net energy expenditure.
For its part, the European FABRIC project has also worked intensively on these issues with a consortium of 25 organizations, among which the CIRCE Foundation also participates as a Spanish reference in this field. We have asked Bludszuweit to describe the experience in the project to us: “FABRIC has shown that dynamic inductive recharging (charging in motion) is possible, although the cost of infrastructure is very high and the horizon for commercial systems is beyond 10 years. In addition, it requires the full development of static recharge beforehand. “
In its development, in any case, FABRIC drew clear conclusions regarding the interoperability of the infrastructure by different types of vehicle. “It has been seen that, for now, low power systems are not interoperable with higher powers (> 20 kW). However, the most recent trends suggest that electric cars will be ready for fast charging, which is why it is likely that on public roads the standard could be 50 kW and this would allow interoperable systemsfrom compact cars to vans and buses. “
With the popularization of electric vehicles it is expected to achieve increasingly competitive prices also for all your infrastructures associated. The first step, of course, is to reduce the prices of batteries to make vehicles more and more affordable, as well as to create a recharging network that allows users to use the electric car as a true substitute for batteries. combustion.
In a complementary way, wireless charging must progressively become a competitive technology able to coexist with the conductive charging system. For this, Carlos Pueyo points out that the “standardization of recharges at powers higher than 20kW, allowing interoperable systems and, of course, reducing the cost of technology. The latter will be achieved once the system manufacturing scale economy“Without a doubt, the progress in the state of this technology, with the strong involvement of institutions and companies, will give much to talk about in the coming years.
Images | BMW, MIT, NJO, CIRCE Foundation, Qualcomm