Wireless Charging of Electric Vehicles

Wireless Charging of

Electric VehiclesPresented by:Kush KulshresthaEEE Section-IUE124027

What are EVs ?An electric vehicle (EV), also referred to as an electric drive vehicle, uses one or more electric motors or traction motors for propulsion. An electric vehicle may be powered through a collector system by electricity from off-vehicle sources, or may be self-contained with a battery or generator to convert fuel to electricity. EVs include road and rail vehicles, surface and underwater vessels, electric aircraft and electric spacecraft. [1]

Need for EVs Global Warming/Climate Change. Due to release of carbon dioxide by burning of fossil fuels.

Rising Prizes. Due to depletion of the reserves of Oil and Natural Gas.

Acid Rain Due to Sulphur Dioxode released by burning of fossil fuels.

Effect on Human Health. Air polution from vehicles and coal powered power palnts.

Impact on Aquitic Life by Oil Spills.

Problem with EVs

Battery technology is expensive because batteries in electric cars need to be able to hold massive amounts of charge to make the cars practical for most drivers. So they are made for expensive materials which are tough to procure. [2]

1

Affordability

SolutionElectric cars could be less expensive if electric car makers could ramp up production volume and use economies of scale. This will happen over time.

Problem with EVs

People are worried about how far they can travel in electric cars before their batteries peter out as most production electric cars about to hit the market can only go about 100 miles (160.9 kilometres) on a single charge. [3]

2

Range Anxiety

SolutionProvide access to a specialized charging station which are currently in short supply.

Problem with EVs

While some charging stations are out in trial phases, most charging still needs to be at home, in a garage. That means that people who live in shared housing or use street parking will likely have the hardest time charging.

3

Charging Stations

SolutionImproving the infra structure and providing more public charging stations on highways and in cities.

Types of Charging Systems

Conductive Charging

It utilizes connector between the Electric power source and vehicle battery.This type of charging is utilized in Residential areas.

Inductive Charging

Wireless charging coupled with magnetic resonance to transfer power from a transmitting pad to a receiving pad

Battery Switching

Depleted EV battery pack is switched with a fully charged battery pack in the switching station.

Wireless Charging or Inductive Charging

The technology depends on the same principle of electromagnetic induction that enables a transformer to change the voltage of an alternating current. This current flows through one coil of wire, creating a magnetic field whose polarity reverses with each cycle and inducing a corresponding alternating field in a secondary coil.Transformers usually include an iron-rich core, which links the coils and increases the field strength, but you don’t really need it. If the two coils are separated by air, current flowing through the first coil will still create a magnetic field, which will still be picked up by the second coil—it just won’t be picked up as well. The greater the air gap, the less efficient the transfer of power will be.



The Problem

In 1994, the Partners for Advanced Transit and Highways project, led by researchers at the University of California, Berkeley, demonstrated the transfer of power from coils buried in the road to the cars above.[4] The receiving coils were on the underside of the test vehicles and were separated from the transmitting coils by an air gap of only 7.5 centimeters.

They captured 65 percent of the injected power, but a scheme that wastes 35 percent of the power could not be brought to the market.How, then, to increase the efficiency of the power transfer without having to make the low-slung receivers even more vulnerable??

Magnetic Resonance Coupling

◇ When a transmitting coil sends electromagnetic waves tuned to a frequency matching the resonance of a circuit holding a receiving coil, it will transfer energy to it very efficiently.


The Solution

In 2007, MIT professors caught the world’s attention by powering a light bulb suspended in space, 2 meters away from the transmitting coil. Those researchers went on to found a Massachusetts start-up, WiTricity Corp., which is working with several auto companies on wireless charging stations for household garages. Quebec’s Bombardier is developing its Primove system in Europe to transmit power to public buses and trams.[5]

Magnetically Coupled Resonancein EV’s


Success Case Study: OLEV Developed by KAIST

On 9 March 2010, researchers from The Korea Advanced Institute of Science and Technology (KAIST) launched Online Electric Vehicle (OLEV), a public transport system using a “recharging road“. Electric power strips have been buried 30 cm (11.8 in) under the road surface and connected to the national grid. Pick-up equipment underneath the vehicle then collects power through non-contact magnetic induction which is used either to power the vehicle prime-mover or for battery charging. As the tram rolls along, magnetic sensors in the road detect its approach and activate the transmitters to send 62 kilowatts to the receiving coils on the underside of the tram. The bus still contains a battery, but it carries 40 percent less energy than it would have to otherwise. It’s also 6 percent lighter and significantly cheaper.


Success Case Study: OLEV Developed by KAIST

Key Advances made by the team: Design of the Electromagnetic FieldAn engineer can choose the relative strength of the two components fields – electric and magnetic. Increase in efficiency of Power Transmission using shaped Magnetic FieldThe path of the magnetic field from the transmitter coil to the receiver coil is guided by the presence of the ferrite cores on both sides.

As a result, the OLEV bus was charged while it was being driven, its body 20 cm above the road, and achieved an average transfer efficiency of 75 percent.


Further Modifications / Future Scope:

By embedding the transmission coils at points where vehicles stop and linger, like parking garages, taxi stands, traffic lights, the vehicles can be charged more efficiently and investments in construction can be reduced. Hence charging at places where vehicles stand a lot of time standing gives a boost to the efficiency.

By selecting the resonance frequency in kilohertz range, a proportionally higher voltage is generated in the receiving coils and gain better transfer efficiency. But increasing the frequency above the megahertz range, the cables for the transmitting and receiving coils could suffer from Skin Effect, which is very less in Kilohertz range.[6]


Challenges to be solved:

EfficiencyAlthough Magnetic Resonance Coupling has increased the efficiency of wireless power transmission to the EVs up to 75 percent, still 25 percent of the energy is wasted. Improving this efficiency up to 90 percent is very essential if wireless charging is to be used on a huge scale.

Heat GeneratedFor High Power transfer system like in railways, the heat generated in the system is very large and difficult to remove.


Challenges to be solved:

Compact DesignHow to make the pickup module light and compact enough to use in small air-gap trains, trams, buses, and cars is the next challenge.

Cost ReductionIn order to make the system of wireless transmission of power to EVs feasible for large scale use, the developers have to drastically reduce the cost of the system by finding inexpensive ways to build the components. Currently, construction of Km loop at the zoo, costs around $550,000.

References

◇ [1] https://en.wikipedia.org/wiki/Electric_vehicle◇ [2] http://auto.howstuffworks.com/challenges-facing-the-electric-car-

industry.htm◇ [3] http://www.cheatsheet.com/automobiles/5-problems-standing-in-the-way-

of-electric-vehicle-adoption.html/?a=viewall◇ [4] http://spectrum.ieee.org/transportation/advanced-cars/the-allelectric-car-

you-never-plug-in◇ [5] http://spectrum.ieee.org/transportation/advanced-cars/the-allelectric-car-

you-never-plug-in◇ [6] http://www.wirelesspowerconsortium.com/technology/magnetic-

resonance-and-magnetic-induction-making-the-right-choice-for-your-application.html

Thanks!Any questions?Find me at:

◇ [email protected]◇ kushkul.wordpress.com

Engineering

Wireless Charging of Electric Vehicles