WIRELESS DYNAMIC
CHARGING FOR
ELECTRIC VEHICLES
1. ABSTRACT
A wireless power transfer (WPT) system makes drivers free from
plugging into electric vehicles (EVs), thus bringing safety, convenience,
and easiness to the drivers. A Resonant Inductive Coupling WPT system
has been considered as a main stream in terms of research and
development lately.
To implement it, the vehicleside coil installed on an EV is required to
be small in size, light in weight, and efficient in power transfer, as well
as tolerant of lateral misalignment with a large air gap. The transmitter
or the road side coil is also needed to be as eficient as possible. Battery
charging module is not an exception too. As a result of our intensive
background research we have got different inspirations regarding the
design of primary and secondary coils and the battery charging module.
The ultimate goal of our capstone project is to develop a system which
will get its supply mainly from solar installations with a back up from
grid.
In our first prototype we are developing the system to work solar
independent.
Figure 1 The concept of the proposed prototype
2. PROBLEM DEFINITION
The problem all EV users face is mostly related to the charging issues
of the EV storage. Here in this project we set out to discover a way
which we believe would enable the EV users to charge their cars as they
are in the go. Currently the EV charging technology takes 6-12 hours
under normal conditions and if using the fastest available super chargers
it takes the battery 40 mins to reach it’s 80% capacity.
3. LITERATURE REVIEW
3.1 Transmitter / road side coil
Resonant inductive coupling or magnetic resonance coupling is another
form of the WPT technologies in which power is transferred between
two tuned resonant circuits, one in the transmitter and the other tuned
circuit in the receiver as depicted in Figure 2. Each resonant circuit
comprises an inductor connected to a capacitor to resonate and couple
the transmitted power at their resonance frequency. This resonance is
responsible for emphasizing the quality factor (Q-factor) for the resonant
circuit. Therefore, the coupling and the power transfer efficiency
between the transmitter and receiver increase due to the directly
proportional relationship between them. Magnetic resonance coupling
scheme is applied in midrange applications such as charging electric
vehicles, charging portable devices, biomedical implants, powering
busses, trains, RFID, smartcards. Several studies have invested in the
resonant inductive coupling technique for enhancement the power
transfer efficiency of WPT systems.
Figure 2 schematic diagram of resonant inductive coupling
3.2 Receiver/vehicle side coil
The onboard subsystem for power receiving is to be composed of a pick-
up coil, a secondary capacitor, a rectifier and a regulator to feed the
battery. This subsystem should be small in size, compact and light in
weight.
An open problem with this technology is the variation of the coupling
factor as a vehicle switches from one transmitting coil to another during
its motion. The transmitter and receiver coils are rarely perfectly aligned
due to the EV movement. Therefore, the
coupling factor between the coils is strongly variable, being dependent
on the position of the onboard receiver coil relative to the fixed position
of the transmitter coil. Since the coupling factor is time variant, there are
some reciprocal positions/instants where it is at
its maximum (perfect alignment of the coils), but there are also other
positions/instants where it is close to zero (large misalignment of the
coils or deactivated transmitter coil). This results in significant power
variation with spikes and holes. In order to overcome these issues, a new
architecture is here proposed based on two pick-up coils mounted in the
vehicle underneath. These identical receiver coils are placed in different
positions under the vehicle (one in front and the other in the rear) and
are activated one at a time so that inductive coupling is always good
enough. This innovative configuration has two main advantages:
1 .it maintains a nearly constant coupling factor, as well as
efficiency and transferred power, as the vehicle moves along the
electrified road;
2. it significantly reduces the cost of road infrastructure.
The results of the investigation show the significant improvement
achieved in terms of maximum power variation which is nearly stable
with the proposed two-coil architecture (only 2.8% variation) while
there are many power holes with the traditional single coil architecture.
In addition, the number of the required transmitting coils is significantly
reduced due to a larger separation between adjacent coils. The first
advantage of the proposed approach is the reduction in the number of
Ground Assembly coils required, with a significant reduction in the cost
of the infrastructure. In addition, charging power and efficiency are
nearly constant with a dual benefit for the AC grid and for the vehicle
where the battery is charged with a constant current, reducing battery
stress and improving its lifespan.
Figure 3 charging principle at different instances
3.3 Battery charging module
Figure 4 bms schematic diagram
A battery management system (BMS) is any electronic system that
manages a rechargeable battery (cell or battery pack), such as by
protecting the battery from operating outside , monitoring its state,
calculating secondary data, reporting that data, controlling its
environment, authenticating it and / or balancing it.
A battery pack built together with a battery management system with an
external communication data bus is a smart battery pack. A smart battery
pack must be charged by a smart battery charger which can specifically
take care of each battery inside the battery pack.
Who certifies or accredits our design?
Regulatory and Supervision Bureau is under the supervision of the
Dubai Supreme Council of Energy. Its responsibilities include the
accreditation of energy service companies and the licensing of new
companies investing in the energy sector in Dubai.
4. Need Identification (Design
Requirement Analysis)
The final design needs to include all the following components as part of
its working system for a reliable and sustainable service.
1. Transmitter-receiver pairs.
2. Solar based power source
3. Proximity sensor to minimize losses
4. External Energy Storage to provide during rainy days or nights.
However for this level of our development we decide to develop the
design independent of solar power and proximity sensor is also not
attached.
Our target goal for this stage of our design is as below
a. Fully functional transmitter –receiver coupling
b. Functional battery charging system
5. DELIVERABLES
1. Transmitter-receiver pairs: the transmitter side will be built by the
service providing company which might be the government or
other privately owned company. However, the secondary coil or
the receiver end will be attached to the EV.
2. Solar based power source: in order to minimize the demand of this
much load from the grid, we decided to power our system mainly
from solar panels.
3. Proximity sensor to minimize losses: this proximity sensor will
turn on the next transmitter when the EV is close enough, so that
loss can be minimized.
4. External Energy Storage to provide during rainy days or nights: at
times where energy is harvested from the sun, we believe it would
be helpful to store it in huge capacity batteries so that can be used
for later demands or no-sun times.
References
Rashid, M. (2018). Power Electronics hand-book. oxford :
Butterworth-Heineman.
Tommaso Campi, S. C. (2021). Two-Coil Receiver for Electrical
Vehicles in Dynamic Wireless. Energies.
