A
PROJECT REPORT
on
Dynamic Wireless Power Transfer with Micro Grid System
By:
Gaurav Kumar Chaubey
Gaurav Kumar Chaubey
Abstract
Vehicles
running on fossil fuel cause a significant amount of air pollution. In order to
reduce the vehicle caused air pollution, electric vehicles are coming up as one
of the preferred alternatives. However, the major drawback of electric vehicles
is the need to charge them frequently. Therefore, long distance travel with an
electric vehicle is a challenge. Thus, it necessitates the need of an
ecofriendly charging system for electric vehicles. An Electrical vehicle can make
use of a power transfer system to charge the on-board Rechargeable Energy
Storage System (RESS – the battery) or to provide power to the electric motor.
It is also possible to use wireless power transfer to charge the batteries
while stationary, using charging “pads”. Both of these solutions are adequate
for charging at home or in car parks but still require the vehicle to stop in
an appropriate location to charge the battery. We propose an ecofriendly
wireless charging system for electric vehicle which enables wireless charging
of the vehicle while running on the highways. The proposed system can also be
used for charging of cars in the shopping malls and other parking places.
Moreover,
the proposed charging system receives required electrical energy from solar PV system
and wind turbines, installed along the highways. The solar PV system and wind
turbines are connected to form a microgrid system and feeds generated
electrical energy to wireless charging system. The surplus electrical energy
may, either be fed back to the main grid or used for highway illumination. The
wireless charging system also consists of air-core transformer with its primary
winding below the highway surface and secondary mounted on the vehicle. The ac
power from secondary passes through rectifier and dc-dc conversion stage to
produce suitable dc voltage and current for the charging of battery unit.
Date: 27 March 2017
TABLE OF CONTENTS
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|||||||
CONTENTS
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Page No.
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Acknowledgement
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i
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||||||
Abstracts
|
ii
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||||||
Table of Contents
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iii
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CHAPTER 1
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INTRODUCTION
|
6-7
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1.1 The
project
1.2 Methodology
and Approach
1.3 Project
team and partners
|
6
6-7
7
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||||||
CHAPTER
2
|
Functional
Requirements
2.1 Introduction to Dynamic Wireless Power
Transfer technologies
2.2 Qualitative
considerations on the DWPT deployment
2.3 Installation of Main Grid and Micro Grid
2.4 Automatic
Identification of Electrical Vehicle
|
7-11
7-8
9
9-10
10-11
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CHAPTER
3
|
Guidance
for installation of DWPT equipment into vehicles
|
11-13
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3.1 Assessment of information on
key components
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11-12
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||||||
3.2 Secondary (pick up) coil
|
12
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3.3 Control electronics
3.4 Power electronics
3.5 Vehicle control strategy and
battery management system (BMS)
|
13
13
13
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CHAPTER
4
|
Power
demand requirements for each vehicle
|
14-21
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4.1 Car and HGV requirements
|
14-15
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||||||
4.2 Power transfer rate from
DWPT
|
15-19
|
||||||
4.2.1 DWPT system layout 1
4.2.2 DWPT system layout 2
4.2.3 Further assumptions
4.3 Assessment of power
requirements
4.4 Scenario A (medium
penetration)
|
16-17
17-18
18-19
19
19-21
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CHAPTER
5
|
Conclusions
and discussion
|
21-23
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CHAPTER
6
|
References
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23-24
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LIST OF FIGURES
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Figure No.
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Figure Name
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Page No.
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Figure 1
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Methodology overview
|
6
|
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Figure 2
|
Examples of powertrains that can be used with dynamic power transfer
|
7
|
|||||
Figure 3
|
Types of power transfer solutions
|
8
|
|||||
Figure 4
|
Dynamic
wireless charging topology
|
9
|
|||||
Figure 5
|
Main Grid and Mini Grid Inter Connection
|
9
|
|||||
Figure 6
|
Automatic Identification of an EV
|
10
|
|||||
Figure 7
|
Example of DWPT system layout
|
16
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|||||
Figure 8
|
Example of DWPT layout 2
|
17
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Figure 9
|
Power demand per mile of motorway for 30% light vehicle and 50%
|
19
|
|||||
Figure 10
|
Power demand per mile of motorway for 30% light vehicle and 50%
heavy vehicle penetration at 55 mph, DWPT system layout 2
|
20
|
|||||
LIST OF TABLES
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|||||||
Table No.
|
Table Name
|
Page No.
|
|||||
Table 1
|
Example of
DWPT system layout 1 power transfer assumptions
|
17
|
|||||
Table 2
|
Example of
DWPT system layout 2 power transfer assumptions
|
18
|
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Introduction
1.1 The
project
In order to avoid the most severe climate change, it
is widely accepted that world-wide emission of greenhouse gases must be halved
by 2050, and the Indian government has committed itself to reducing CO2
emissions by 80% by 2050. In 2013, Big amount of India’s CO2 emissions were
from transport. There is a clear move towards accelerated introduction of Low
Carbon Vehicles. Although the Indian and European governments’ policies are
technology agnostic and focus on supporting any technologies that are able to meet government objectives, particular attention has recently been placed on electrified vehicles, as evidenced by the DfT’s policies, such as Plugged-in-Places and Plugged-inCar/Van grants in the India which specifies what alternative fuels infrastructure should be deployed by the Member States, with particularly high targets for EV charging infrastructure in the latter. At the same time, many of the world’s leading automotive manufacturers are making significant long-term investments into electro-mobility, which are indicative of a growing and maturing market.
technology agnostic and focus on supporting any technologies that are able to meet government objectives, particular attention has recently been placed on electrified vehicles, as evidenced by the DfT’s policies, such as Plugged-in-Places and Plugged-inCar/Van grants in the India which specifies what alternative fuels infrastructure should be deployed by the Member States, with particularly high targets for EV charging infrastructure in the latter. At the same time, many of the world’s leading automotive manufacturers are making significant long-term investments into electro-mobility, which are indicative of a growing and maturing market.
In 2012, major roads in England (Motorways and A-roads) carried two thirds of the traffic (65.5%), with motorways seeing continued growth since 2010. Therefore, Highways England (previously known as the Highways Agency), as operator of the Strategic Road Network (SRN), is in a prime position to facilitate and support the transition to Electric Vehicles. At the same time, the implementation of Dynamic Wireless Power Transfer (DWPT) may open up opportunities for providing additional services to the users of the SRN and, in the process, create an additional revenue stream for Highways England that can support wider implementation of this programme and therefore, higher benefits.
DWPT is being considered first (ahead of other technologies such as rapid battery charging and overhead conductive charging) for a number of reasons. It could potentially be implemented on all vehicle classes and types (unlike some conductive charging options, such as, catenary-based systems). It overcomes issues (whether real or perceived) with battery performance by receiving power on the move. Because DWPT systems can be installed under the road without any additional visible infrastructure, they do not introduce additional safety risks (collision or electrical safety) and potentially minimize the need for maintenance.
This project aims to inform Highways India of this potentially environmentally friendly solution that will provide a safe road environment for the projected growth in electric/hybrid vehicles using the Strategic Road Network.
1.2
Methodology and Approach
Figure 1: Methodology overview
Phase 1 of the project focused on
undertaking a comprehensive stakeholder engagement programme with potential
private and commercial vehicle and system users. During this phase the scope of
the feasibility study was also finalised.
Phase 2 focused on requirements
identification for the DWPT system as a whole and also on its integration into
the road, different vehicle types and connection to the electric grid.
Phase 3 built on stakeholder
engagement from Phase 1 and combined it with preliminary project outputs that
could be shared with stakeholders to seek further, more informed feedback on
attitudes towards DWPT.
Phase
4 focused on preparing for off-road trials of DWPT technology in the UK that
were expected to follow the feasibility study in future stages of the research
programme.
Phase
5 was dedicated to carrying out a comprehensive impacts assessment of
introducing DWPT on the SRN in England. It covered environmental, economic and
financial aspects for introduction of DWPT in different use cases.
1.3
Project team and partners
The novelty and complexity of the project required a
multidisciplinary team of experts to fully address all of the elements of the
feasibility study. TRL selected and led a team of experts from around the world
to support TRL in the delivery of the aims and objectives of this study.
Functional
Requirements
2.1 Introduction to Dynamic Wireless
Power Transfer technologies
The main focus of this section is to identify
possible DWPT technologies that would be suitable for taking forward to an
off-road trial in the UK and their key characteristics / performance
parameters; identify and characterise
potential other services; and analyse the impacts of dynamic DWPT on other
electrical services.
Figure
2: Examples of powertrains that can be used with dynamic power transfer
For
all electrified vehicle powertrain options, including hybrid powertrains, a
vehicle can make use of a power transfer system to charge the on-board
Rechargeable Energy Storage System (RESS – the battery) or to provide power to
the electric motor. Typically, such power transfer systems are plug-in electric
chargers (as shown in Figure 8a) that charge the vehicle batteries at varying
levels of power (usually between 3kW and 50kW, although some, like the Tesla
supercharger can go up to 120kW) while the vehicle is stationary and switched
off. However, it is also possible to use wireless power transfer to charge the
batteries while stationary, using charging “pads” as shown in Figure 8b. Both
of these solutions are adequate for charging at home or in car parks but still
require the vehicle to stop in an appropriate location to charge the battery.
Dynamic power transfer is another option for supplying power to electric
vehicles and, as it can be used while the vehicle is moving, it can help to
reduce or eliminate issues with restricted range. Dynamic power transfer can be either
conductive (as shown in Figure 8c) or wireless (as shown in Figure 8d). It can
be used to supply the electric motor with power directly or to charge the
on-board RESS, or both, as shown in Figure 2.
Conductive dynamic power
transfer is only practical for vehicles of a certain size (in the case of
pantograph solutions) and requires a considerable amount of over ground
infrastructure and cables, which could present a considerable maintenance
challenge and a potential safety hazard. In the case of in-road conductive rail
systems, there are some substantial issues associated with electrical safety
and operational durability of such systems if deployed in the motorway
environment. Therefore, for the purpose of this project, the feasibility of WPT
systems is considered.
(a)
Plug-in charging system
|
(b) Wireless
power transfer,
stationary state
|
|
(c) Charging for conduction on-road (Scania)
|
(d) Wireless power transfer on-road (KAIST)
|
|
Figure 3: Types of power transfer
solutions
2.2 Qualitative considerations on the DWPT deployment
A road equipped with a DWPT system can be represented as in
Figure 9: at the roadside, substations receive electric current from the grid
and they adapt it in order to feed the primary circuits embedded in the road.
Figure 4: Dynamic
wireless charging topology
It is assumed that the required power transfer level from a
DWPT system on a motorway is around 20kW to 40kW per vehicle for cars and light
vans, and between 100kW and 180kW for trucks and coaches, based on the power
required to maintain constant motorway speed.
2.3 Installation of Main Grid and Micro Grid
Main Grid and Smart Mini Grid To give supply to the power transfer loops,
it will need to connect through some sustainable power supply. Both the main
and smart mini grid system is going to use within the Dynamic Wireless Power
Transfer technology. A Smart Mini-Grid system is an application of digital
technology which optimizes electrical power generation and delivery. The system
is based on the integration of multiple distributed energy resources (DERs)
into the same grid. This system is also based on intelligent load and energy
resource management.
Figure 5: Main Grid and Mini Grid Inter Connection
It is designed with local controllers for each of the distributed
generation technologies as well as a central controller called intelligent
dispatch controller (IDC) which communicates with each local controller.
Whereas the local controllers ensure maximum utilization of energy resources
with permissible output power, the IDC performs complex system control
functions and takes critical decisions such as automating the demand response,
dynamically adding or removing DERs in a seamless manner (based on the existing
demand) without affecting the grid stability.
2.4 Automatic Identification of Electrical
Vehicle
Figure 7 shows a typical
DWPT system. A vehicle approaches the DWPT segments (orange blocks below road
surface), the secondary coils on the vehicle are shown in orange between the
wheels. Grid power is supplied to the DWPT system’s local power control via a
local sub-station (purple lines). The power control system is in contact with a
DWPT back office for control and billing purposes. Figure 60 also shows a means
for the infrastructure to communicate with the vehicle before (antenna 1),
during (antennas 2-4) and at the end of the DWPT segment (antenna 5). Not all
DWPT systems will necessarily include this type of communications link.
Figure 6: Automatic Identification of an EV
As a vehicle equipped with
DWPT approaches a segment of road equipped with the necessary power
infrastructure, the infrastructure needs to recognise that a suitably equipped
vehicle is approaching. This normally implies a communications channel exists
between the vehicle (A) and the infrastructure (antenna 1). In the example
shown in Figure, this is achieved by a radio channel. This recognition could in
principal also be achieved without a communications channel, for example using
an ANPR camera. Once the infrastructure has recognised the vehicle, it will
have the basic information it needs to transfer power, i.e.:
•
What the power transfer capabilities of the vehicle
are
•
Whether a valid account exists to pay for the
power
•
Whether the vehicle requires power (the batteries may
be fully charged)
•
How much power
the vehicle requires (if the batteries are fully charged, the vehicle may still
want to accept enough power to directly power the traction motors).
The last two points may not
be possible for a recognition system which does not employ a communications
channel between the vehicle and the infrastructure.
Also shown in Figure 60 are
regular communications antennas which will enable the infrastructure to continually
monitor the vehicle to ensure that the power transfer is continuing correctly.
As before, this is not used by all DWPT systems, so cannot be assumed to exist.
Any systems which do not include the regular exchange of information between
the infrastructure and the vehicle must demonstrate that fault conditions are
adequately coped with.
Assuming the infrastructure
has determined that power needs to be supplied to the vehicle, it must now
determine when to turn on the primary power coils. It is normally required that
the primary coils are only energised when the secondary coils are a position
which allows them to couple fully with the primary coils (vehicle B). This
maximises both efficiency and safety by containing the magnetic fields within
the space between the primary and secondary coils. It is important however to
understand that not all systems may work in this way, so this cannot be
assumed.
Power will now be
transferred while the vehicle drives over the primary coils. When the vehicle
is not in a position which allows inductive coupling between the primary and
secondary (e.g. Vehicle C), no power should be applied to the primary
coil.
3.1 Assessment of
information on key components
There are three basic
ways of implementing wireless power transfer infrastructure:
1) Charging at base; Home, work, depot
(vehicle stationary)
2) On road static charging (vehicle
stationary)
3) On road dynamic power transfer
(vehicle moving).
From the vehicle perspective, the key components
should be the same for all wireless power transfer methods. The variations in
key component parameters are associated with the type of wireless power
transfer implemented, as described above, the amount of power transferred and
the voltage rating of the on-board battery. Control of battery charging takes
place by means of an on-board battery management system (BMS). There should be
a communication link between the BMS, the on-board pick up coil and the roadside
supply equipment.
For dynamic power transfer, the vehicle control
strategy is different from charging at base or static charging. The control system needs to decide when to
use WPT technology for charging the battery and/or driving the electric motor,
and whether regenerative energy from vehicle braking should be prioritised over
WPT for charging the battery. This section of the report focuses specifically
on the on-board components of a DWPT system. The key system components that
need to be fitted to the vehicle are:
1. Secondary pick up coil(s)
2. Control electronics
3. Power electronics (e.g. rectifier,
inverter) to charge the battery or power the electric traction motor.
It is likely that some of these components will be
integrated into a single assembly. In addition to DWPT hardware, the control
strategy within the vehicle control unit will require modification. Accurate
alignment of the primary and secondary coils optimises the power transfer
efficiency. Some vehicles may also include a means of assisting the driver to
accurately position the on-board secondary coil to align with the in-road
primary coils, although this is not considered to be an essential part of a
DWPT system.
The sections below describe requirements for each of
the main components identified in more detail.
Other components which are not specifically discussed
as they are not a strictly necessary part of a DWPT system, but which would be
used in a fully functioning market ready solution, include:
•
Communication
modules – most EVs and modern vehicle have built-in communication capability so
this is not considered to be a major additional component
•
Billing
systems / back office – there are a number of billing and back office systems
already in use for applications such as congestion charging, road tolling or
road pricing and mobile phone billing
•
Additional
safety systems to monitor use of infrastructure – these may not be necessary
and will depend on each manufacturer’s approach to ensuring safety
•
Shielding
from EMF – this is likely to be a necessary component but its exact
specification will depend on the specific requirements of the vehicle and the
DWPT system implemented
•
Energy
storage systems – most EVs and Hybrid vehicles already use such systems so they
are not considered as components required specifically for DWPT.
3.2 Secondary (pick
up) coil
The
size of the secondary coil is dependent on three main factors:
•
Type
of system and operating frequency. Systems based on magnetic resonance are more
efficient than standard inductive charging and, as such, are likely to have
smaller coils for a given power transfer rate. They are also not as dependent
as the standard inductive charging system on accurate alignment of the primary
and secondary coils, and can typically accommodate misalignment in the x and y
axis of up to 15cm.
•
Level
of power transfer. Coils for aftermarket residential systems with relatively
low levels of power transfer (single figure kilowatts) will be much smaller
than those aimed at static and dynamic bus systems (hundreds of kilowatts).
Rather than one large pad, some systems use a number of smaller pads connected
in parallel.
•
Air
gap between the coils. The gap between the primary and secondary coils will
affect the size of the secondary coil. To maintain a given power level and
efficiency, as the air gap increases, the size of the secondary coil will also
increase.
Based on a number of systems investigated during the
project, secondary coil sizes were found to differ considerably, with the pads
(housing containing the coil wires, necessary connections and any ferrite
material) ranging in size from approximately 40cm x 40cm to 220cm x 90 cm. Most
secondary coil assemblies were between 8 and 12 cm in thickness.
Some manufacturers use multi-secondary coil
arrangements on the vehicle in order to achieve higher levels of power pick up,
using anywhere between 1 and 5 coils to achieve total power transfer of up to
140kW for DWPT.
In
comparison, low power (up to 7kW) static WPT secondary coils designed for cars
are much smaller, between 25cm x 25cm and 40cm x 40cm.
3.3 Control electronics
The
control electronics consist of a low power control module based on a
microcontroller. This would be a relatively small unit and would need to be
powered from the vehicle 12V system when the vehicle battery is being charged.
The control electronics module is likely to be based on the CAN (Controller
Area Network) interface.
3.4 Power electronics
Three main factors determine the specification of the
power electronics:
•
Vehicle
battery voltage
•
Maximum
charge current which is dependent on the ability of the vehicle battery to
accept charge without overheating
•
The
level of power that is transmitted by the WPT system.
For high levels of power transfer, active cooling of
the power electronics is likely. For most DWPT systems, power electronics will
consist of a rectifier and a regulator. In addition, it may be necessary to
include a transformer if the power from the secondary coil is used to power the
traction motor directly.
Rectifiers can vary in size depending on the power
level they are designed for and whether they have built-in cooling systems.
They can currently comprise a single unit of approximately 80cm x 80cm x 15cm
(width x depth x height) and weight of approximately 55kg, with the potential
to be significantly reduced in size in future.
A
DC-DC converter for low voltage power supply (and to even out the voltage and
current supply) is also required.
3.5
Vehicle control strategy and battery management
system (BMS)
Accurate control of the battery State Of Charge (SOC)
is essential on both hybrid and full electric vehicles in order to maximise the
battery life and accurately calculate vehicle range.
Calculation
of SOC is done within the battery pack by the battery management system and for
this calculation it needs information regarding the energy put into the battery
and taken out of the battery. For electric vehicles with a wired charging
system, this is straightforward as there is only one source of energy output
(to the high voltage supply network) and two mutually exclusive sources of
energy input: • Energy from the electrical
machine during regenerative braking
• Energy from the battery charger.
Regenerative braking can only occur when the vehicle
is moving which is mutually exclusive with the battery charger being connected
(or static charging from a wireless charging system), which can only happen
when the vehicle is stationary.
With DWPT this is not the case as it is possible that
regenerative braking and DWPT could occur at the same time. This is not
desirable and must be managed. This situation is analogous to hybrid vehicles
where energy can be supplied from regenerative braking and the combustion
engine simultaneously. Under this condition the control strategy within the
vehicle control unit decides on which source of energy is best used to charge
the battery or power the motors. For battery electric vehicles this function is
not present and would need to be added if the vehicle is to support DWPT.
Furthermore, currently, charging protocols used by all
EVs for the on-board charger that is connected to external power supply dictate
that the vehicle must be stationary when the vehicle is receiving power form an
external source. This is a fail-safe measure designed to prevent vehicles from
driving off while they are being charged. For DWPT, a new interface would need
to exist, in addition to the plug-in charging interface, to allow power to be
transmitted to the vehicle while it is moving.
Power demand requirements for each
vehicle
This section describes the
power demand requirements for different vehicle types and differing scenarios
on the SRN. Power demand requirements were estimated using DfT and TRL data
sets in order to understand potential power demand from a DWPT equipped motorway.
Using data obtained at earlier stages in the project and data from partner
organisations, a high level model was used to understand variations in power
demand. A sensitivity analysis was used to understand the variations that will
be created by differing traffic conditions (traffic density) by time of day.
It is necessary to understand how much power is
required by different vehicle types in order to maintain their speed on the
motorway of up to 70mph. In order to be useful, DWPT systems will need to be
able to supply power at least at this level to the vehicles. If less power is
available then the vehicle will need to use additional power from other
sources, such as an on-board ICE, rechargeable energy storage system (REES) or
a Fuel Cell. This would result in the vehicle either not being able to maintain
100% electric traction, thereby using additional fuel, or, using energy stored
in their REES. If more power is available than the vehicle requires, then it is
possible that an on-board REES can be charged while providing full traction to
the vehicle.
4.1 Car and HGV requirements
The power requirements from a typical modern EV family
car (the Nissan Leaf is used as a representative vehicle) at different constant
speeds were calculated and are shown in Table 12. This shows both the power
required for traction to maintain the constant speed, and the power required
from the grid, which accounts for the various losses incurred between the grid
and the traction motor. The wheel to grid efficiency is assumed to be 73% when
the DWPT is used to provide traction power to the vehicle. At constant speed,
the variation in the kinetic energy is zero, and the energy required for
acceleration is not included in the table. It can be observed that at 50 mph
the vehicle requires about 12 kW from the grid to maintain a constant speed,
and that the power requirement more than doubles if the speed rises to 70 mph.
This is due to a non-linear increase in air resistance with higher vehicle
speed, thus requiring more power to maintain the speed.
Table 1: Car or light vehicle
energy demand under various constant speeds
Speed (mph)
|
Speed (m/s)
|
Power requirement
for traction
(kW)
|
Traction energy per km
(kWh)
|
Power
demand from the grid (kW)
|
10
|
4.5
|
1.1
|
0.067
|
1.5
|
20
|
8.9
|
2.2
|
0.067
|
3.0
|
30
|
13.4
|
3.7
|
0.076
|
5.0
|
40
|
17.9
|
5.8
|
0.090
|
7.9
|
50
|
22.3
|
8.8
|
0.11
|
12.0
|
55
|
24.6
|
10.7
|
0.12
|
14.6
|
60
|
26.8
|
12.8
|
0.13
|
17.6
|
65
|
29.1
|
15.8
|
0.15
|
21.7
|
70
|
31.3
|
18.1
|
0.16
|
24.8
|
75
|
33.5
|
21.3
|
0.18
|
29.2
|
80
|
35.8
|
24.9
|
0.19
|
34.1
|
Air resistance is even more important for HGVs, due to
the less aerodynamic shape of the vehicle. As the speed increases, the air
resistance increases and becomes the dominant cause of energy consumption
beyond 55 mph. The Scania R-series truck was used as a typical HGV for which,
as shown in Table 13, the power demand from the grid is about 175 kW when
travelling at 55 mph.
Table 2: HGV energy demand under various constant speeds
Speed (mph)
|
Speed (m/s)
|
Power
requirement for traction (kW)
|
Traction energy per km
(kWh)
|
Power demand
from the
Grid (kW)
|
10
|
4.5
|
11.7
|
0.73
|
16.1
|
20
|
8.9
|
25.6
|
0.80
|
35.1
|
30
|
13.4
|
44.3
|
0.92
|
60.7
|
40
|
17.9
|
70.2
|
1.09
|
96.2
|
45
|
20.1
|
86.6
|
1.20
|
118.7
|
50
|
22.3
|
105.7
|
1.31
|
144.7
|
55
|
24.6
|
127.8
|
1.44
|
175.0
|
57
|
25.5
|
137.6
|
1.50
|
188.4
|
60
|
26.8
|
153.1
|
1.59
|
209.7
|
65
|
29.1
|
182.1
|
1.74
|
249.5
|
70
|
31.3
|
214.9
|
1.91
|
294.4
|
4.2 Power transfer rate from DWPT
In order to explore what power is to be provided by
the grid, it is important to consider not only the power requirements of the
vehicles but also the maximum power that can be delivered by a DWPT system.
Based on the information available about the systems reviewed, it is apparent
that for different systems there is a different combination of power supply,
power transfer segment length (that can only be occupied by a single vehicle)
and gaps between power transfer segments.
Two different topologies for system layout are
described below.
4.2.1 DWPT system layout
1
In the example layout shown in Figure 8, each segment
can be occupied by up to two different vehicles, separated by approximately 25
m.
Figure 7: Example of DWPT system layout
Each vehicle can receive a maximum of 100 kW. Because
the analysis is focussed on future scenarios, an assumption is made that both
light vehicles and heavy vehicles can use the same infrastructure, which would
result in them drawing different levels of power from the grid. These are
summarised in Table 14 below. It should be noted that a more detailed
investigation of how a vehicle powertrain could deal with the amount of power
provided by DWPT can be found in Section 6).
The table shows that light vehicles similar to the
Nissan Leaf would use 14.6 kW for maintaining 55 mph speed on the motorway.
Vans and larger light vehicles would likely require more power to maintain
speed. The model assumes that up to 40 kW is transferred to the on-board
vehicle coil. Power that is not used for maintaining speed would be used to
charge the battery. For HGVs, 175 kW of power is required to maintain this
speed. This is more than is available from system layout 1.
Table 1: Example
of DWPT system layout 1 power transfer assumptions
Vehicle class
|
Traction power required from grid at 55mph
|
Assumed power
received by
secondary
coil
|
Assumed
power drawn
from the grid
|
Comments
|
Light vehicles (car or van)
|
14.6kW
|
Up to
40kW
|
51kVA
|
The
traction power value is based on a car (specifically the Nissan Leaf). Vans
would likely require more traction power than the stated 14.6kW. Any spare
power is assumed to be used for charging batteries on the move.
|
Heavy vehicles (Trucks or coaches)
|
175kW
|
100kW
|
118kVA
|
This
category includes a large variety of vehicles. Medium sized trucks and
coaches are likely to not require more than 100kW. Very heavy vehicles, such
as articulated lorries will likely need an additional source of power
on-board the vehicle.
|
4.2.2 DWPT system layout 2
In the example layout shown in Figure 33, each segment
can be occupied by up to one vehicle only. The distance between segments is
short compared to the segment length, of the order of 2 to 5 m.
Figure 8: Example of DWPT layout 2
The gap between vehicles has to be maintained at 40 m
in order to avoid the system switching off due to the presence of a
non-equipped vehicle. Each vehicle can receive a maximum of 140 kW. As
previously, an assumption is made that both light vehicles and heavy vehicles
can use the same infrastructure, which would result in them drawing different
levels of power from the grid. These are summarised in Table 15. It should be
noted that a more detailed investigation of how a vehicle powertrain could deal
with the amount of power provided by DWPT can be found in Section 6).
Table 15: Example
of DWPT system layout 2 power transfer assumptions
Vehicle class
|
Traction power required from grid at 55mph
|
Assumed power
received by
secondary
coil
|
Assumed power
drawn
from the grid
|
Comments
|
Light 14.6kW
vehicles
(car or
van)
|
Up
40kW
|
to
51kVA
|
The
traction power value is based on a car (specifically the Nissan Leaf). Vans
would likely require more power than stated 14.6kW. Any spare power is
assumed to be used for charging batteries on the move.
|
|
Heavy 175kW
vehicles (Trucks or coaches)
|
140kW
|
184kVA
|
This
category includes a large variety of vehicles. Medium sized trucks and
coaches are likely to not require more than 140kW. Very heavy vehicles, such
as articulated lorries will likely need an additional source of power
on-board the vehicle.
|
4.2.3 Further
assumptions
In order to estimate total power demand it is
necessary to define a specific use case by making a series of assumptions about
how a DWPT system may be deployed in an operational environment. The use case
situation we have chosen to illustrate is listed below:
• A single lane of motorway is equipped
with a WPT system (left lane)
• Only data from three lane motorways
is used in order to maintain consistency with maximum traffic density o Data from MIDAS points on M6, M42,
M69, M6 toll are used
• Maximum vehicle flows are the maximum
number recorded within one hour of data
• Secondary coil to grid efficiency is
80%
• Power factor is 0.972
• All vehicles are prepared to travel
at 55mph maximum speed when charging.
4.3 Assessment of power
requirements
One of the largest sources of uncertainty in this
analysis is the assumed penetration rates of equipped vehicles. There is no
data on which the penetration can be estimated as there are no precedents for
the adoption of such vehicle technology. Therefore, two scenarios were created
that represent a medium level of take up and a high level of take up of the
technology by vehicle users and operators. Furthermore, it also assumed that
the deployment of DWPT systems would be targeting the users that could benefit
most from the technology. As the provisional findings from the preliminary
benefits to cost ratio analysis suggest that the benefit of the system is
proportional to the total annual mileage driven, vehicles with the highest
mileage could therefore benefit the most. As a result, an assumption is made
that a higher proportion of high-mileage fleet vehicles (such as long haul
trucks and heavy coaches) will be equipped with DWPT capability than cars and
vans. Assumptions for DWPT capability penetration rates are summarised
below:
• Scenario A (medium penetration) o Light vehicles: 30% o Heavy vehicles: 50%
• Scenario B (high penetration) o Light vehicles: 50%
• Heavy vehicles: 75%.
The sections below describe the expected power demand
for each scenario based on the assumptions and the method outlined in preceding
sections.
4.4 Scenario A (medium penetration)
Figure 10 and Figure 11 below illustrate power demand
profiles for layout 1 and layout 2.
Figure 9: Power demand per mile of motorway for 30%
light vehicle and 50%
heavy vehicle penetration at 55 mph, DWPT
system layout 1
Figure 10: Power demand
per mile of motorway for 30% light vehicle and 50% heavy vehicle penetration at
55 mph, DWPT system layout 2
Analysis of the expected demand profiles shows that
the average power demand generally follows the same profile as road traffic, with
an increase during the morning peak and then continued demand at a lower
baseline with another increase towards the evening peak and then a drop towards
night time. It should be noted that the average demand profile is very similar
for both DWPT system layout examples, having similar peak values at around
0.5MVA and is constant through the day between 0.3 and 0.4MVA per mile.
However, the maximum power demand profiles are
substantially different between the two system layout examples. In the case of
system layout 1 (Figure 10), there is a very pronounced morning peak, reaching
4MVA per mile, and then a sharp drop to around 1.5MVA followed by a smaller
evening peak of approximately 3MVA. This profile suggests that system layout 1
is sensitive to fluctuations in vehicle densities per mile section of the
motorway. Due to the relatively high number of individual power transfer
segments in this layout, up to 64 segments per mile, vehicle density becomes
the dominant factor determining maximum power demand. Closer examination of the
results shows that the highest utilisation of power transfer segments is 82%
(equivalent to approximately 53 of the available power transfer segments being
occupied during that hour). As the vehicle density reduces, so does the total
maximum power demand.
System layout 2 generates a different maximum power
demand profile, as seen in Figure 33. This is more uniform between the morning
and evening traffic peaks, with the maximum power demand in the morning
reaching just over 2MVA, continuing at around 2MVA for the rest of the day and
increasing towards 2.5MVA in the evening peak before dropping at night. The
maximum power demand is lower than for system layout 1. This is due to layout 2
having fewer (but longer) individual power transfer segments per mile of
motorway, up to 36 segments. Therefore, the system reaches high levels of
utilisation more quickly, and on numerous occasions reaches a point where more
vehicles require power transfer than there are available segments. This is the limiting
factor for system layout 2 where 100% utilisation is reached between the hours
of 7am and 10am. So, although there are more vehicles present on that stretch
of the motorway able to use the system, they are not able to draw power due to
lack of available power transfer segments. This is an important limitation to
bear in mind because during later stage of adoption when DWPT vehicle
penetration is high, inability to guarantee power to vehicles using DWPT
because of close proximity of other vehicles may have a significant negative
impact on battery electric vehicle range relying on the DWPT system.
The difference between the two example layouts only
manifests itself when considering maximum power demand because there are
instances under these conditions when utilisation exceeds 100%. When looking at
average power demand, the profiles are very similar because utilisation is far
below 100% on average, meaning that it does not become a limiting factor for
either layout and so the profiles are similar to that of average vehicle flow
rates. System layout 2 has a slightly higher average power demand due to the
slightly higher power transfer capability per segment.
These values depend on all vehicles using the DWPT
lane travelling at 55mph. This speed has been selected as a limiting factor in
that, above this speed, overcoming air resistance becomes the dominant power
draw. This is also the approximate speed limit for HGVs on the UK road network.
In assuming this value for HGVs, and that there is a single lane equipped with
DWPT technology, it becomes the case that light vehicles must also travel at
this speed if they are to using this lane to charge.
Conclusions and discussion
Following a review of the impacts that would need to
be taken into account in a costbenefit analysis of DWPT, it was concluded that
a full appraisal would need to consider the following:
•
Costs
to the ‘broader transport budget’ (Highways England):
o
The
DWPT equipment costs and installation o A connection to the distribution grid
o Maintenance o User administration and ‘back office
costs’ o Electricity charges from the grid
•
Indirect
taxation impacts on central government finances:
o
Loss
of fuel duty
o
Loss
of VAT on fuel saved by private users
•
Business
impacts:
o
The
cost of DWPT vehicles in comparison with conventional ones o Fuel cost savings
•
Social
impacts:
o
The
cost of DWPT vehicles in comparison with conventional ones o Fuel cost savings
•
Environmental
impacts:
o The ‘non traded’ carbon price of CO2
savings (taking account of CO2 emissions from electricity production)
o
The
monetised benefits of reduced NOx and PM emissions (which vary
according to the exposed population and background air quality)
For the purpose of this report costs to business and
users were not calculated. Such a calculation would also require information on
the likely cost of DWPT vehicles, for which there is currently very little
robust information. This report therefore focuses on assessing what the costs
of providing a DWPT system might be under a chosen scenario, to both transport
budgets and central government finances, and the monetised environmental
benefits from reduced emissions.
For the chosen scenario, based on steadily increased
penetration of DWPT vehicles into the traffic mix of representative sections of
motorway, the following conclusions were reached (for a 20 year appraisal
period):
•
The
Net Present Value of construction and operating costs, per km, would be ₹1200 M, of which infrastructure costs
(which includes the 60% ‘optimism bias’) account for 30% and electricity 70%.
•
In
this scenario, the NPV of monetised CO2 savings would be nearly ₹10000M per km, equivalent to half the
capital cost. This corresponds to approximately 45% reduction in emissions
compared with the ‘without DWPT’ case.
•
Local
emissions of NOx and PM would be reduced, in this scenario, by
approximately 35% and 40% respectively. The NPV monetised value of these
reductions would be less than £100k, except in areas where populations are
exposed to poor air quality. Where the NO2 limit is exceeded, the
value of NOx reductions would rise to over a million pounds per km
over the appraisal period, although this would not be expected to apply to more
than a few locations on the SRN.
•
There
would be a reduction of around ₹1000M in central government revenue, because of the ‘loss’ of
fuel duty and VAT from reduced fuel consumption. This is greater than the
capital costs of the fixed infrastructure.
A
number of other potential impacts were identified qualitatively, but were not
considered further because of a lack of information. However, some would
require further investigation as part of any assessment of a proposed scheme,
in particular any relating to the maintenance implications of the road, and
potential changes in road user behaviour, or demand for transport that might
occur.
Uncertainties and
limitations in the model
It is important to bear in mind that the model outputs
are based upon current forecasts of fuel and electricity prices, assumptions
that could change significantly in the longer term, particularly if, for
example, the need to reduce carbon emissions more quickly leads to the
introduction of carbon pricing in transport.
As noted above, the costs to users have not been
assessed in this report. To do this it will necessary to understand more about
the DWPT vehicles themselves, both in terms of their performance as well as
their costs:
•
The
technology is not yet commercially developed so a market price has not yet
emerged. Whatever the technologies adopted, unit costs will be significantly
lower than those in any experimental vehicles, especially at the high uptake
rates used in the later years of our scenarios.
•
It
is not clear what will be the ‘baseline’ vehicle against which DWPT costs
should be compared. If tighter emissions regulations in the future make ICE
vehicles more expensive, or lead to a greater push towards hybrid and EV
technology, then the price ‘gap’ to DWPT capability will be greatly reduced.
•
The
model is based upon representative values for only two vehicle types: HGV and
light vehicles, the latter being based upon power consumption for a car. There
remains considerable uncertainty on how LGVs might be adapted for DWPT, whether
as compatible EVs, as is assumed for cars, or as hybrids, as assumed for HGVs.
•
The
widespread availability of DWPT could influence the design and hence costs of
EV and hybrid vehicles, potentially reducing the size of the battery needed for
full EVs or the maximum diesel engine power needed for a hybrid, if motorway
running could be largely shifted to DWPT operation.
There are other drivers that could support a business
case, in particular the growing need for low and zero emission vehicles in
urban areas. If a broader environmental case such as this is being made for
buying an EV or plug in hybrid, then the availability of DWPT on motorways will
support that case, as the running costs per km will be lower than for a
conventional vehicle even at the higher mark-ups on electricity charges
considered in this study.
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