International Journal of Engineering Trends and Technology (IJETT) – Volume 16 Number 5 – Oct 2014
Car Park Charger Using Witricity
Adarsh Srinivas#1, Deepak Gadodia#2, Sahil Kadam#3, Vaibhav Chauhan#4
#
Undergraduate Student, Electronics and Telecommunication Department,D.J.Sanghvi College of Engineering
Mumbai, Maharashtra, India
Abstract— This paper is a survey on the various techniques of
wireless charging which can be improvised in a car park charger
like Inductive Power Transfer (IPT) system and Magnetic
Resonant Coupling (MRC).Although there has been a lot of
research done in this area, there are many possibilities not
explored yet and also it is not clear to new researchers where and
how to start. This paper also focuses on the safety considerations
of wireless charging for Electric Vehicles including potential
electrical shock hazards, magnetic field exposure hazards,
misalignment, overcharging etc. It also recommends one of the
possible solutions to overcome the limitation of overcharging in a
wireless car park charger.
Keywords—: IPT, MRC
the EV and the primary coil is embedded in the floor of a
garage, parking space, or in the street. The basic principle of
an inductively coupled power transfer system is shown in
Figure 1. It consists of a transmitter coil L1 and a receiver coil
L2. Both coils form a system of magnetically coupled
inductors. An alternating current in the transmitter coil
generates a magnetic field which induces a voltage in the
receiver coil. This voltage can be used to power a mobile
device or charge a battery.
The efficiency of the power transfer depends on the coupling
(k) between the inductors and their quality (Q). The coupling
is determined by the distance between the inductors (z) and
the ratio of D2 /D. The coupling is further determined by the
shape of the coils and the angle between them.
Introduction
Wireless power transmission is a promising technology which
attracts attention in many fields and products. With mobile
electronic products being prevalent, such as cell phones and
PDAs, removing the power cord becomes a natural
progression of achieving the ultimate mobility of the product.
Wireless chargers for Electric Vehicles (EVs) would also be a
convenient feature, avoiding any need to remember to plug in
a power cord after parking the vehicle.[2] Additional safety
advantages may also be achieved due to eliminating exposed
contacts. Nevertheless, wireless charging for EVs is an
application requiring high electrical power (up to hundreds of
kilowatts) and larger area of wireless power transmission
which increases electromagnetic field exposure. Thus,
application of wireless charging to an EV requires a
comprehensive analysis to ensure consumer safety. This paper
focuses on the safety considerations of wireless charging for
EVs, including potential electrical shock hazards, magnetic
field exposure hazards, fire hazards, etc.[1] It provides a
historical background of wireless charging, particularly for
Electric Vehicles
II .Wireless Charging Techniques
In this paper, we discuss two wireless charging technologies
applicable for Electric vehicles.
1. Inductive Power Transfer
One technology uses an inductive coupling method, also
known as the inductive power transfer (IPT) system. As
shown in Figure 1, such a system is composed by a primary
coil, a secondary coil, and a rectifier to convert the AC power
into DC power. The secondary coil is placed on and carried by
ISSN: 2231-5381
2. Magnetic Resonant Coupling
The source drives a primary coil, creating a sinusoidally
varying magnetic field, which induces a voltage across the
terminals of a secondary coil, and thus transfers power to a
load. This mechanism, responsible for power transferring a
transformer, where the magnetic field is typically confined to
a high permeability core, also functions when the region
between the primary and secondary coils is simply air.[4]
Inductive coupling without high permeability cores is used,
for example ,to power RF ID tags and medical implants. A
common technique for increasing the voltage received by the
device to be powered to add a parallel capacitor to the
secondary to form a resonant circuit at the operating
frequency. Magnetic resonant coupling can be used to deliver
power from a large source coil to one or many small load coils,
with lumped capacitors at the coil terminals providing a
simple means to match resonant frequencies for the coils. This
mechanism is potentially robust means for delivering wireless
power to multiple receivers from a single large-source coil .A
relatively simple circuit model describes the essential features
of the resonant coupling interaction, with parameters that can
be either derived from first principle descriptions, from direct
measurement or from curve fitting techniques. A key issue for
http://www.ijettjournal.org
Page 200
International Journal of Engineering Trends and Technology (IJETT) – Volume 16 Number 5 – Oct 2014
powering of multiple receivers is the coupled mode frequency
splitting that occurs when two receivers are in close enough
proximity that their magnetic fields are relatively strongly
coupled. Control circuitry to track the resonant frequency
shifts and to retune the receiving coil capacitances is a
potentially viable strategy for addressing this issue.
potential fire hazards[1]. These concerns are primarily due to
the presence of large power levels, large electromagnetic
fields, and operation in potentially hazardous locations (for
example, operation in garages with flammable materials).
Overcharging:
It is the most common and safest type of side-effect but not
the only thing that can happen. A battery can quite simply die
from being overcharged. An overcharged battery will boil the
sulfuric acid and distilled water mix. The casing of the battery
can become hot to the touch, and begin to melt or swell.
Flammable hydrogen can build up inside the sealed cells of
the battery, causing swelling of the casing under pressure and
seepage through small vents. Once the hydrogen is introduced
to oxygen, it becomes a sitting time bomb. A small electrical
spark can ignite the gas and cause the battery to explode,
sending plastic and lead shrapnel flying around, in addition to
a
caustic
sulfuric
acid
spray.
III.Block diagram
Misalignment:
Misalignment of the coils will affect the coupling factor of the
system. As such, this will affect the efficiency of the power
transfer. However, there are also concerns that misalignment
can distort the field in a way that would allow the field to
stretch or extend into an adjacent zone [5]. For example, the
user cannot be located under the vehicle during charging, but
can be located in next to or within the vehicle. If misalignment
can cause the field to extend from under the vehicle into the
user occupied area next to the vehicle, then a hazardous
condition could exist. If this is the case, then misalignment of
the coils would become a safety critical issue. Maximum
misalignment would need to be controlled for more than just
efficiency, and the means to control or mitigate misalignment
would become a safety critical system.
Field Exposure:
Block Diagram of Electromagnetic Induction based Car
Park and Charge demonstrating charging technique.
IV. Safety considerations and hazards:
Wireless charging is accomplished through a coupling of the
primary and secondary coils. This involves the generation of
electrical and magnetic fields that can be potentially
dangerous to the user or others in the vicinity of the vehicle
while charging.[3]
Although wireless charging systems has many advantages for
EV charging, the technology also poses potentially significant
safety concerns such as electrical shock due to the high
electrical power, high magnetic field exposure to the general
public that may exceed standards and FCC regulations, and
ISSN: 2231-5381
Electromagnetic field (EMF) exposure is a major concern for
wireless charging for EVs. EMF exposure need to be
rigorously analysed to be within acceptable levels specified
by safety standards, both under normal conditions as well as
unusual conditions such as during abnormal operation,
presence of a human under the vehicle, potential abuse, etc.[1]
For the driver and passengers in the car, the radiation hazard
may be less concerned due to the shielding of metal on the
chassis of the car. However, there is a possibility that humans
or animals may be present underneath the car during charging
and therefore be exposed to high levels of electromagnetic
radiation. The “radiation zone” of the wireless charger for EV
is in the near field of the electromagnetic wave, since both
IPT and MRC operate in the near field of the EMF source
versus far field which is used for transmitting
signals/information for antennas. Exposures in the near field
are more difficult to specify because both E and H fields must
be studied or measured separately, and because the field
patterns are more complicated. Apparently, the most
hazardous radiation zone is right between the two coils, and
http://www.ijettjournal.org
Page 201
International Journal of Engineering Trends and Technology (IJETT) – Volume 16 Number 5 – Oct 2014
secondary hazardous zone is around the coils (not right over
the coils but still under the car). These areas are the most
hazardous zones but it is noted that they are not directly
exposed to humans or animals at all time. Comparing with
these areas, another important hazardous zone in need of
consideration is near the charger and around the car (not under
the car), and it exposes to the general public directly. This
area along with the two hazardous areas under the car needs to
be considered during the design cycle.
V. Solutions
The most common way of wearing out of a battery is due to
overcharging and the resultant cell damage. To avoid this, we
recommend the use of a relay timer circuit which allows us to
set the time duration of charging of the battery. The circuit
works in manner that it gets automatically disconnected after
the specified time interval provided by us. The figure below is
the circuit diagram of the relay timer circuit. A temperature
signal, or a resettable fuse, can be used to turn off or
disconnect the charger when danger signs appear to avoid
damaging the battery. This simple additional safety precaution
is particularly important for high power batteries where the
consequences of failure can be both serious and expensive.
The solutions don't just involve the development of chargers,
they involve the design and roll out of a network of public and
private charging stations with associated user authentication
and billing systems, public safety and planning issues, the
negotiation of international standards and beefing up the
electricity grid to carry the increased load. There are no single
answers to these issues. On the one hand, national and
international standards organisations attempt to find definitive
solutions to these issues, but there are so many competing
national standards. On the other hand commercial enterprises
attempt to leapfrog the competition by coming up with new
and unique innovative solutions to differentiate their offerings.
VI. Conclusion and Future
scope:
Witricity’s technology is a non-radiative mode of energy
transfer, relying instead on the magnetic near field. Magnetic
fields interact very weakly with biological organisms—
people and animals—and are scientifically regarded to be
safe. Witricity products are being designed to comply with
applicable safety standards and regulations .Hence Witricity
is a safe technology. Witricity can transfer power depending
on the source and receiver. if they are relatively close to one
another, it can exceed 95%.Efficiency is primarily
determined by the distance between the power source and
capture device, however, the shape may impact the efficiency.
The city just has to be covered with Witricity hot spots
wherein you can use your electric gadget battery and wire
free making it more convenient to carry around and much
lighter. With Witricity, there will be no need of charging
batteries, or buying new batteries for your electrical gadgets.
There will be no need of power cables and batteries. The
concept can be further explored on the lines of OLEV
wherein the vehicle can be dynamically charged along the
road using hotspot pads.
VII. References
[1] White Paper by Hai Jiang, Paul Brazis Jr., Mahmood
Tabaddor and Joseph Bablo, Safety Considerations of
Wireless Charger for Electric Vehicles – A Review Paper
[2] Dr. Morris Kesler WiTricity Corporation, Highly Resonant
Wireless Power Transfer: Safe, Efficient, and over Distance
[3] Matthew A. Bloom, GengNiu, Mahesh Krishnamurthy
Electric Drives and Energy Conversion Lab, Department of
Electrical and Computer Engineering, Illinois Institute of
Technology, Design Considerations for Wireless Electric
Vehicle Charging
[4]A. Kurs, A. Karalis, R.Moffatt, J. D. Joannopoulos, P.
Fisher, and M. Soljacic,“Wireless power transfer via strongly
coupled magnetic resonances,” Science, vol. 317, pp. 83–86,
Jul. 6, 2007.
[5] K. Kim, Y. Ryu, E. Park, K. Song and C. Ahn "Analysis of
Misalignments in Efficiency of Mid-Range Magnetic
Resonance Wireless Power Link", Proc. IEEE AP-S Int. Symp.
Dig., Chicago IL, July, 2012.
ISSN: 2231-5381
http://www.ijettjournal.org
Page 202