A Review on Charging Systems for Electric Vehicles in Smart Cities

Mohamed A. Abd El Ghany

1,2

Electronics Department, German University in Cairo, Egypt

Integrated Electronic Systems Lab, TU Darmstadt, Germany

Keywords: Electric Vehicle, Charging System, V2V, Wireless Power Transfer.

Abstract: An overview of types of electric vehicles and the variant batteries which the electric vehicles currently use is

demonstrated. Different charging systems are presented. Plug-in charging system which is either on-board or

off board is investigated. Moreover, fundamentals of wireless charging are analyzed for smart cities. Current

market perspectives are provided. A hybrid charging system is also discussed. Different approaches for

vehicle to vehicle charging either using plug or wireless charging are provided.

1 INTRODUCTION

Batteries are the main energy source of electric

vehicles (EVs). However, some types of EVs also

rely on other energetic components. Many systems

have been developed for charging Electric Vehicles

(EVs) batteries. The main two technologies are Plug-

In (Turksoy, et al., 2018) and Wireless charging

Systems (Bosshard, et al, 2016). Plug-in charging

systems are hazardous and pose the danger of electric

shocks (Freschi, et al, 2018); however, they are easier

to implement and mostly have higher efficiency.

Wireless Chargers, on the other hand, are safer and

eliminate the inconvenience imposed by the bulkiness

of the cables. Nonetheless, having the wired (plug-in)

and wireless charging systems available at the same

time is critical, especially before the wireless

charging infrastructure is readily available

(Chinthavali, et al, 2016).

Wireless power transfer (WPT) is a convenient

way for electric and plug-in hybrid electric vehicle

charging that has seen rapid growth in recent years for

stationary and even dynamic applications. The size of

the couplers in WPT systems can be reduced and the

power transfer density increased by designing the

systems to operate at higher frequencies. Higher

operating frequencies also enable smaller power

electronics associated with WPT systems (as shown

in Figure 1) thanks to a decrease in energy storage

requirements.

Today, real-time charging from the utility grid is

recognized to be the mainstream way of ’fueling’

electric vehicles (EVs). However, since the current

EV penetration rates are very limited, many of the

problems such as increased distribution level peak

demand. Studies show that residential EV charging

will result in disruptive problems in the distribution

grid of the future (Cuchý, et al, 2018), (Graber, et al,

2018), (Chentong, et al, 2019), (Luigi, et al, 2019), and

(Veneri,et al, 2017). This indicates that residential EV

charging must be accompanied by faster public

stations to sustain the EV growth.

Vehicle-to-vehicle (V2V) Charge Sharing

Network (CSN) philosophy can provide an

alternative, more convenient, and flexible way of

conducting EV charging. The design and

implementation of V2V CSN will greatly reduce the

range anxiety of EVs with minimal infrastructure cost

(Ucer, et al, 2019).

This survey is organized into 7 sections. Section I

provides a brief introduction to the topic this study is

concerned with. An overview of types of EVs and

batteries is given in section II. Section III discusses

plug-in charging systems. Fundamentals of wireless

power transfer and wireless charging systems along

with market analysis is given section IV. Further,

section V gives a unique overview of combining the

wired and wireless charging systems. Section VI

discuss the concept of vehicle to vehicle charging.

The conclusion of this survey and possible future

work is highlighted in section VII

El Ghany, M.

A Review on Charging Systems for Electric Vehicles in Smart Cities.

DOI: 10.5220/0010463105710578

In Proceedings of the 7th International Conference on Vehicle Technology and Intelligent Transport Systems (VEHITS 2021), pages 571-578

ISBN: 978-989-758-513-5

571

2 TYPES OF ELECTRIC

VEHICLES

Batteries are the main energy source of EVs but some

types of EVs also rely on other energetic components.

Thus, there may be some EVs which work with

electric propulsion alone while others also employ an

Internal Combustion Engine (ICE). On that basis, the

Technical Committee 69 of the International

Electrotechnical Commission (IEC) has established

the following classification of electric vehicles

running with batteries:

• Battery Electric Vehicle (BEV). Power is

inserted into the drive train exclusively by

means of batteries.

• Hybrid electric vehicle (HEV). This refers to

vehicles with two or more types of energy

source or storage, providing one of them with

electrical energy.

• Plug-in Hybrid Electric Vehicle (PHEV). This

type of vehicle mainly uses the electrical power

train to run.

Battery Technology in EVs. Batteries are the main

storage element used in EVs. These elements make it

possible to store energy in chemical form and convert

it to electrical energy when required. The

characteristics of the batteries, such as the density of

energy and power, are defined by the technology

used. Although many of them have characteristics

that meet the criteria of electric vehicles, power is

usually a limiting factor for some tasks such as

acceleration and regenerative braking.

The battery technology used in electric vehicles

has evolved over time, especially in recent years with

the emergence of large vehicle manufacturers in this

market. Lead-acid batteries were the first type of

battery used to start the internal combustion engines

in vehicles. Some manufacturers, such as Toyota and

General Motors, have tested this technology in BEVs.

However, the low energy density of this kind of

battery does not make them suitable for pure EVs.

ZEBRA batteries, also known as molten salt batteries,

have been used for some vehicle concepts and urban

bus models (O’Sullivan, et al, 2006). These batteries

have a good energy density, but they need to operate

at high temperatures (between 270 and 350 C). This

restriction means that this technology is only viable

in vehicles with a continuous operation in order to

maintain the working temperature.

NiMH technology has been widely used in the

market (Iclodean, et al, 2017). Despite the low

efficiency of this technology and a slightly higher

weight than others, its good energy and power density

combined with its simplicity, low cost and useful

lifetime make it a good solution for HEVs and

PHEVs. However, Lithium-ion or simply Li-ion

batteries are the market leaders thanks to their

electrical features. Within this group of batteries, we

find a wide variety of different types. The types of Li-

ion batteries vary according to the specific chemical

combination found at the anode and the cathode.

Although the combination most widely used in

consumer applications is Lithium-Cobalt Oxide

(LCO), its use does not extend to electric vehicles due

to safety concerns. Instead, the most common

solutions for automotive applications are lithium-

nickel-manganese-cobalt (NMC), lithium-nickel-

cobalt-aluminum (NCA) and lithium-iron phosphate

(LFP). Table 1 summaries the main electrical features

of the batteries discussed above (Kumar, et al, 2017).

Table 1: Comparative Table of Electric Vehicle Batteries.

Nominal

Power

Life

Production

Voltage(V)

(Wh/Kg)

Cycle

Cost/60 KWh

Lead acid

180

1000

$4,800

Nickel-metal

1.2

200-300

<3000

$20,000

Hybrid

ZEBRA

2.6

155

>1200

$19,600

Li-ion

3.6

200-430

2000

$12,000

Li-iron

3.2

2000-4500

>1200

$28,000

Phosphate

3 PLUG-IN CHARGING

SYSTEMS

This section gives a quick overview of plug-in battery

charging systems for electric vehicles. Battery

Chargers can be categorized into two main categories,

on-board and off-board, with the two options of

unidirectional and bidirectional power transfer, this is

decided according to the place where the charger is

installed (Turksoy, et al., 2018).

Battery chargers are a kind of power converter

that supplies power from the network to the battery

pack. The charger usually creates a non-linear load in

the power system. Charging the battery with high

efficiency is not the only concern of a well-designed

charger, but also to meet the international standards

(Pan, et al, 2017). The comparisons of on-board vs.

off-board battery charger features are given in Table

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572

Table 2: The comparison of On-board vs. Off-board battery

chargers.

Figure 1: Circuit topology of bridgeless interleaved boost

PFC. (Turksoy, et al., 2018).

Unidirectional charger is a power converter with

simple control structure where the power is supplied

in only one direction from the network to the battery

pack; while bidirectional battery chargers are power

converters that charge the battery pack from the

network and transmit this power to the grid when the

network needs it (Tashakor et al, 2017). The

characteristics of the battery charger affects the

battery life and charge time.

The first stage of a two-stage EV battery charger

carries out the AC DC conversion with power factor

correction (PFC). The second stage is DC-DC

converter which is convert the output DC voltage

level of AC-DC PFC converter to the battery DC

voltage level (Chen, et al, 2011). Figures 1 and 2

show the topologies of a PFC and a DC-DC

converter.

The safety of EVs users may be challenged by the

vehicle’s increased operating voltages, at different

frequencies, possibly making the protection against

direct and indirect contacts more complex. As a

result, plug-in EVs must meet minimum safety

requirements. Consumer safety may be affected by

various hazards associated with human interaction

with these vehicles, including chemical, collision,

electrical, and fire risks. The chemical hazard is

associated with a given battery technology and stems

from the potential chemical release of the battery’s

reactive constituents, with which people may come

into con-tact (Freschi, et al, 2018).

Figure 2: Interleaved Buck-boost DC-DC converter

(Turksoy, et al., 2018).

4 WIRELESS CHARGING

SYSTEMS

4.1 Fundamentals of Wireless Power

Transfer

Wireless power transfer is supported by an

electromagnetic wave travelling from the power

emitter to the power receiver. In WPT systems, the

electromagnetic field is exclusively generated to

transfer power. Conversely, energy harvesting

techniques make use of the electromagnetic waves

generated to transfer information to acquire energy to

power devices. Thus, energy harvesting techniques

are restricted to the requirements imposed by the

information transfer, which are not present in WPT

technologies.

The behavior of an electromagnetic wave is

defined by Maxwell’s equations. Simplification of

these equations is possible when some conditions

hold, leading to the near-field and far-field operation.

Both scenarios are described next.

Near-field Operation or Non-radiative

Propagation. Three conditions must be satisfied to

work in this kind of scenario. They are:

• The size of the transmitter element, L, is much

smaller than the wavelength λ.

• The distance between the energy emitter and the

receiver is much smaller than the wavelength λ.

• The distance between the transmitter and the

receiver is much smaller than (2L

)= λ.

Far-field Operation or Radiative Propagation.

This is based on the electric field of the

electromagnetic wave. In this case, the conditions are:

• The distance between the energy emitter and the

receiver is greater than the wavelength λ.

• The size of the transmitter element LDEV is

more than 10 times greater than the wavelength

λ.

1) Inductive WPT: Inductive WPT is realized with

the magnetic field of the electromagnetic wave. The

A Review on Charging Systems for Electric Vehicles in Smart Cities

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operation principle is explained by the interaction of

the magnetic and electrical behavior described by

Ampere’s` Law and Faraday’s Law. According to

Ampere’s` Law, a current-carrying wire generates a

magnetic field around it. The intensity of the

magnetic field and its orientation depend on the

topology of the wire. Specifically, Ampere’s` Law (1)

states that:









   (1)

where H is the magnetic field intensity of the

magnetic field generated by the electric current I and

dl is the differential element of length along the path

on which the current travels.

Unlike simple wires, coils are able to concentrate,

to a higher degree, the magnetic field around the area

in which they are defined. As described by Ampere’s`

Law, when a time-varying current passes through a

coil, a time-varying current magnetic field is

generated around this element. If that time-varying

magnetic field traverses a different coil, a voltage

ind

) is induced in its terminals. This effect is

described by Faraday’s Law as follows (2):





 





(2)

where is the flux of the magnetic field passing in

the area limited by the coil. Inductive WPT

technology requires a pair of coils referred to as the

primary and secondary coils.

2) Magnetic Resonance WPT: Magnetic

resonance or resonant WPT can be considered an

improvement on inductive WPT in which the

electrical system is forced to work under resonant

conditions. To meet this requirement, the pair of coils

is connected to structures composed of reactive

elements such as capacitors or additional coils. These

structures are referred to as the compensation

networks.

The most simple compensation topologies consist

of a single capacitor, which may be connected to the

primary and the secondary in series or in parallel.

These networks are referred to as mono-resonant

compensation topologies. Alternative, more complex

compensation topologies are also an option. These are

identified as multi-resonant compensation topologies.

4.2 Wireless Chargers for Electric

Vehicles

Due to the current environmental crisis, there is great

interest in developing new trends in the sustainable

transportation sector. In this context, EVs are

expected to significantly decrease greenhouse gas

emissions and, in turn, lead to a healthier living

\environment. A number of facts support this

prediction. According to the United States

Environmental Protection Agency, nearly 28.9% of

the greenhouse gas emissions of the United States in

2017 were derived from the transportation sector (US

EPA, 2015), (Sato, et al, 2016).

4.3 Wireless Power Transfer Market

Perspectives

Presented below is a review of a number of

technology providers that lead the EV-WPT market

(Choi, et al, 2015):

-WiTricity: WiTricitys 3.6–11 kW EV charging

products show an overall system efficiency of 90–

93%. WiTricity works actively with global

standardization agencies such as SAE International

and IEC/ISO. The WiTricity EV wireless products

offer several charging rates varying from 3.6 to 11

kW to meet different EV battery needs and with a

single system design.

-Qualcomm: This technology offers a power rate

ranging from 3.3 to 20 kW at an overall efficiency

greater than 90%. Qualcomm technology uses

patented innovative technology that enables highly

efficient power transfer even when the charging pads

are not completely aligned.

-Evatran: Evatran offers a 7.2 kW-production

plugless system charging a BMWi3 across 254mm of

clearance. The charging time of different systems is

presented in Table 3.

Table 3: Comparative table of charging times.

4.4 Wireless Charging Systems

The industry has experienced huge progress in

inductive WPT technology for stationary charging of

EVs the past decade (Bosshard, et al, 2016). In

today’s market, stationary chargers are already

available. However, for magnetic flux guidance and

shielding, inductive WPT systems require ferrite

cores. This makes them expensive and bulky. The

operating frequencies are kept under 100 KHz to limit

the losses in the ferrites. This results in low transfer

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power densities and larger coils. The high cost and

low power transfer density pose huge challenges for

dynamic WPT, as these systems need to have very

high power capability in order to deliver sufficient

energy to the vehicle during its very brief time

passing over a charging coil.

For these reasons dynamic inductive WPT is yet

to become commercially viable, although a few

experimental systems have been demonstrated (Choi,

et al, 2015) (Onar, et al, 2013). The inductive WPT is

shown in Figure 3.

Figure 3: Inductive WPT using plates coupled through

electric fields (Choi, et al, 2015).

Achieving effective power transfer limits WPT

systems’ operating frequency to be close to the

resonant frequency of the resonant tank formed by the

reactances (capacitive and inductive) of the coupler

and compensating network. However, the coupler

reactance depends on the vehicle’s road clearance,

and varies as the vehicle moves across the charger. A

reduction in power transfer and WPT system

efficiency is then caused by the drift between the

resonant and operating frequency.

Figure 4: A capacitive wireless power transfer (WPT)

system with an active variable reactance (AVR) rectifier

that can provide continuously variable compensation by

controlling the voltages V

and V

(Regensburger, et al,

2017).

Adaptive impedance matching techniques include the

use of saturable and variable inductors (James, et al,

2005), but these techniques reduce system efficiency

and do not scale well with power. An example of a

high frequency rectifier and inverter architecture, that

compensate for coupling variations , while operating

at fixed frequency and maintaining high efficiency is

the active variable reactance (AVR) rectifier shown

in Figure 4.

By appropriately controlling the output voltages

of its two coupled rectifiers, the AVR can provide

continuously variable compensation while

maintaining optimum soft switching to ensure high

efficiency. This compensation architecture ensures

that the output power of the WPT system is

maintained at a fixed level across wide variations in

coupling and is applicable to both capacitive and

inductive WPT systems.

5 COMBINED WIRED AND

WIRELESS CHARGING

SYSTEMS

This section gives a unique overview of combining

the wired and wireless charging functionalities as

presented in (Chinthavali, et al, 2016). As the number

of EVs increase, the market is in continuous need for

reduction in cost size while increasing the efficiency

and the power rating of on-board chargers. Further,

on- and off-board plug-in chargers pose the hazard of

electric shock along with the heavy weight and large

size of cables. Implementing WPT, ergo having

wireless chargers seems to solve these problems;

however, having the wired (plug-in) and wireless

charging systems available at the same time is critical,

especially before the wireless charging infrastructure

is readily available. Achieving the integrated system

using same components for both charging systems

substantial cost benefits could be achieved

(Chinthavali, et al, 2015).

Figure 5 shows the overall proposed integrated

system. The topology five stages of power conversion

from the wall to the vehicle battery in the wireless

charging mode and four stages in the wired charging

mode.

5.1 Wireless Charging Mode

Figure 6 demonstrates the circuit topology for the

wireless mode of operation. Utility ac power is

converted to controllable dc voltage by the active

front-end rectifier with power factor correction

(PFC). Adjustable dc voltage is applied to the input

of the high frequency (HF) full-bridge inverter with a

controlled duty ratio.

A Review on Charging Systems for Electric Vehicles in Smart Cities

575

Figure 5: Integrated system topology on the circuit level. (US EPA, 2015).

Figure 6: Wireless charging system topology on the circuit level. (US EPA, 2015).

Figure 7: Wired charging system topology on the circuit level. (Chinthavali, et al, 2015).

The HF stage delivers excitation current to a series

tuned primary coil for magnetic field generation that

is linked to the secondary coil on the vehicle across

the air gap. Voltage induced at the secondary is

rectified, filtered, and delivered to the vehicle HV

battery.

5.2 Wired Charging Mode

The HF transformer solution also provides the

flexibility of using the system as a wired charger. This

can be achieved by simply using a relay system that

can be operated to disconnect the resonant coil system

and connect the output of the HF transformer to the

on-board section of the integrated charger system.

The wired charging mode of operation has four power

conversion stages. This mode of operation will enable

the EV users to use the plug-in charger wherever there

is no wireless charging option. Figure 7 shows the

topology for the wired mode of operation

(Chinthavali, et al, 2015).

6 VEHICLE TO VEHICLE

CHARGING SYSTEMS

In the near future, the concept of vehicle to X (V2X),

that is transmitting electricity from an on board

battery to infrastructure, is expected to spread. V2X

is a collective term for such as, vehicle to live (V2L),

vehicle to home (V2H), and vehicle to grid (V2G)

(Panchal, et al, 2018). For example, this can be used

as an emergency power source to charge electric

appliances (Izumi, et al, 2014). V2H and V2G

technologies have started to be put to practical use.

However, in this section the main purpose is to study

the vehicle-to-vehicle technology.

The energy transfer between EVs will be through a

bidirectional DC-DC converter in a conductive way

which can take place at parking lots of workplaces,

campuses, or residential premises and highways. As

proposed by (Cuchý, et al, 2018) the (V2V) Charge

Sharing Network (CSN) philosophy shall provide an

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alternative, more convenient, and flexible way of

conducting EV charging.

V2V charging requires an analysis in terms of

how to match suppliers to receivers with efficient

matching algorithms and how to enable energy

exchange with current EV charging technologies

(Mou, et al, 2018). Three different approaches for

V2V energy transfer have been compared in (Sousa,

et al, 2018): vehicle-to-grid and grid-to-vehicle

(V2G+G2V), V2V over direct ac interconnection

(acV2V), and V2V over dc interconnection (dcV2V).

It was concluded that dcV2V is more efficient than

the other options due to reduced number of energy

conversions.

Figure 8: Bidirectional DC-DC converters for V2V charger

(Cuchý, 2018).

The dc-dc converter topologies investigated in this

paper are non-isolated as there is no grid connection

requirement (Cuchý, et al, 2018). One of the

candidate solutions to this operation is known as

bidirectional dc-dc converters is shown in Figure 8.

As a practical industry example, there is a V2V

charging realized by Andromeda Power using ’Orca

Inceptive’ (Andromeda Power, 2020).

7 CONCLUSIONS

In this survey, different EV battery charging systems

are discussed, along with the various battery types

used for different EVs. A theoretical overview on the

various WPT techniques is provided. Multiple WPT

systems are discussed for smart cities. The overview

of each topology is presented. Research is still needed

on the health effects of long-term exposure to weak

electric and magnetic fields, methods to determine

optimal charger power levels and spacing for cost

effectiveness and approaches to analyze impacts of

large-scale WPT system deployment on the electric

grid.

As for future applications, 3 main concepts shall

be considered. First, Wireless vehicle to grid (W-

V2G) which can offer a solution alongside advanced

scheduling for charging and discharging to the

distribution network.

Secondly, in Wheel wireless charging system

(IW-WCS) where receiver coils are placed in a

parallel combination inside the tire. This technology

can rectify air-gap problems. It has been developed

for both stationary and dynamic applications. The

third application is wireless vehicle-to-vehicle

charging technology structure, where the transmitter

coil and the receiver coil are embedded in the front

and rear of the car, respectively. With a limited

number of charging stations, this technology can be

used to increase charging opportunities through

vehicle-to-vehicle (V2V) charging. At present,

charging stations require regular maintenance and

service to ensure the equipment is working properly.

The wireless V2V charging system can help to solve

this issue. The main issue with the wireless V2V

charging technology is the angular offset due to the

change in the location of the vehicle and the reduced

battery size.

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