A Multi-Criteria Analysis and Trends of Electric Motors for Electric Vehicles

Abstract

The interest in electric traction has reached a very high level in recent decades; there is no doubt that electric vehicles have become among the main means of transport and will be the first choice in the future, but to dominate the market, a lot of research efforts are still devoted to this purpose. Electric machines are crucial components of electric vehicle powertrains. The bulk of traction drive systems have converged in recent years toward having some sort of permanent magnet machines because there is a growing trend toward enhancing the power density and efficiency of traction machines, resulting in unique designs and refinements to fundamental machine topologies, as well as the introduction of new machine classes. This paper presents the technological aspect of the different components of the electric powertrain and highlights the important information on the electric vehicle’s architecture. It focuses on a multi-criteria comparison of different electric motors utilized in the electric traction system to give a clear vision to allow choosing the adequate electrical motor for the desired application. The proposed comparative analysis shows that the induction motor better meets the major necessities of the electric powertrain, whereas the permanent magnet synchronous motor is nonetheless the most used by electric vehicle manufacturers.

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Citation: El Hadraoui, H.; Zegrari,
M.; Chebak, A.; Laayati, O.;
Guennouni, N. A Multi-Criteria
Analysis and Trends of Electric
Motors for Electric Vehicles. World
Electr. Veh. J. 2022,13, 65. https://
doi.org/10.3390/wevj13040065
Academic Editors: Hang Gao and
Joeri Van Mierlo
Received: 8 February 2022
Accepted: 10 March 2022
Published: 7 April 2022
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Article
A Multi-Criteria Analysis and Trends of Electric Motors for
Electric Vehicles
Hicham El Hadraoui 1, * , Mourad Zegrari 1,2, Ahmed Chebak 1, Oussama Laayati 1and Nasr Guennouni 1
1Green Tech Institute (GTI), Mohammed VI Polytechnic University (UM6P), Benguerir 43150, Morocco;
mourad.zegrari@um6p.ma (M.Z.); ahmed.chebak@um6p.ma (A.C.); oussama.laayati@um6p.ma (O.L.);
nasr.guennouni@um6p.ma (N.G.)
2ENSAM Casablanca, Hassan II University of Casablanca, Casablanca 20670, Morocco
*Correspondence: hicham.elhadraoui@um6p.ma or elhadraoui.hi@gmail.com; Tel.: +212-708-035-406
Abstract:
The interest in electric traction has reached a very high level in recent decades; there is
no doubt that electric vehicles have become among the main means of transport and will be the
first choice in the future, but to dominate the market, a lot of research efforts are still devoted to
this purpose. Electric machines are crucial components of electric vehicle powertrains. The bulk of
traction drive systems have converged in recent years toward having some sort of permanent magnet
machines because there is a growing trend toward enhancing the power density and efficiency of
traction machines, resulting in unique designs and refinements to fundamental machine topologies,
as well as the introduction of new machine classes. This paper presents the technological aspect of
the different components of the electric powertrain and highlights the important information on the
electric vehicle’s architecture. It focuses on a multi-criteria comparison of different electric motors
utilized in the electric traction system to give a clear vision to allow choosing the adequate electrical
motor for the desired application. The proposed comparative analysis shows that the induction
motor better meets the major necessities of the electric powertrain, whereas the permanent magnet
synchronous motor is nonetheless the most used by electric vehicle manufacturers.
Keywords:
electric vehicle; electric machine; traction motor; powertrain; power density; efficiency;
reliability; performance criteria
1. Introduction
During recent decades, global warming, reduction in petroleum resources, deteriora-
tion of air quality, and the different inquiries regarding a pollution-free healthy and clean
environment have heightened scientists’ regard for producing alternative sustainable and
environmentally clean solutions. In developing countries, especially in large cities, the
transportation sector is one of the main causes of increasing harmful exhaust emissions in
the environment (i.e., pollutants, such as Particulate Matter (PM), nitrogen oxides (NOX),
CO, and sulfur dioxide (SO
2
)), causing many health troubles. The electrification of vehicle
powertrains is widely seen as a viable way to increase fuel efficiency and reduce greenhouse
gas emissions in the automotive sector [1].
The electric force is the primary source of energy for electric vehicle technology. It is
stored in a storage system, often hybrid, and is converted by the motor into mechanical
energy and then transformed on the vehicle wheels using the best possible transmission
device, which must be characterized by high efficiency, provide the required torque and
speed for the wheels, and be reversible. The most common transmission system for the
electric powertrain is the single-speed gear ratio. The electric motor should give the vital
power to propel the electric vehicle in an efficient way. The choice of an electric motor for
an electric vehicle (EV) chassis is a significant challenge. There are various electric vehicles
available on the market [
2
]. These vehicles incorporate different motors for different
functionalities. EVs may be equipped with alternative current (AC) motors or direct current
World Electr. Veh. J. 2022,13, 65. https://doi.org/10.3390/wevj13040065 https://www.mdpi.com/journal/wevj

World Electr. Veh. J. 2022,13, 65 2 of 28
(DC) motors according to configuration or relying upon the expected utilization. Several
studies have been conducted on the aspect of electric motors, and distinctive kinds have
been created [
3
]. This provides electric vehicle producers with a wide assortment of electric
motors to browse according to their needs. The determination of a specific type of electric
vehicle motor should be done with caution, as the qualities of the motor influence the
overall performance of a vehicle [4].
Many criteria, for example, efficiency, cost, reliability, innovation, and controllability,
must be considered. From the point of view of industrial applications, for electric vehicle
application and more, factors must be taken into account; the most widely recognized
motors used in electric vehicles are permanent magnet synchronous motors, induction
motors, and brushless DC motors [
5
,
6
]. The traction motor candidates for the electric
traction system must meet high-performance, speed sensorless control as a low-cost solution
and must be reliable, efficient, and offer an outstretched point of stability at different
speeds [
7
]. Many reviews reported the recent technologies and challenges of electric and
hybrid vehicles [
1
,
3
] covering the numerous aspects and discussing the challenges and
opportunities to be considered in developing new electric vehicles. This paper focuses
on electric motors and their interactions and presents the recent trends in electric motors
available on the market. In addition, it presents a multi-criteria comparative study of
electrical motors used in electric vehicles. In the first section, the different electric vehicle
architectures and the components of the electric powertrain are introduced. The second
section concerns the literature study of the motors used in electric vehicles. Then, a
comparative analysis of the different electrical motors is performed based on various
criteria that impact numerous aspects, mainly the energy efficiency, electrical characteristics,
robustness, and maintenance factors. Conclusions are then made to identify the potential
candidate electric motor for the electric traction system.
2. Electric Traction System
The architecture of the electric vehicle alludes to the disposition of the energy storage
system and the components of the electric powertrain. The architecture of the EV is more
flexible than a conventional internal combustion engine (ICE) vehicle’s architecture due to
the reduction of the moving parts; the clutch and the conventional transmission system are
substituted by a simple gear ratio, in addition to the simplification of the ICE system [8].
2.1. Electrical Vehicle Powertrain Architecture
The energy flow in EVs is achieved with flexible electrical cabling and the minimum
of moving mechanical linkages. Figure 1shows the detailed basic configuration of an
electric traction system. The principal constituents of an electric powertrain are the power
source, the electronic controllers, the electric motor, the transmission system, and the
onboard charger for batteries. The secondary power supply of electric vehicles provides the
power required for all auxiliary systems, mainly the temperature control units that monitor
the favorable temperature of the battery system for its long-running time and the power
steering units [9].

World Electr. Veh. J. 2022,13, 65 3 of 28
Figure 1. Vehicle powertrain architecture.
2.1.1. Charging System
Electric cars can be recharged by alternative or continuous current in respective normal
charging or fast charging. At home, we are dealing with an alternating current that will
have to pass through an on-board charger; this is what limits the recharging capacity
because the internal rectifier cannot have a large capacity, and this is limited to a little more
than 20 kW for the best-equipped cars—in general, it is around the 10 kW limit for a good
electrical installation that allows going up to this level. Basically, a conventional outlet
delivers 2.7 kW although the car can take more. Superchargers are direct current and do
not need to go through an internal converter in the car; the recharging capacity can then be
enormous, exceeding 250 kW [10,11].
2.1.2. Energy Sources
The main families of direct electrical storage systems are the accumulators that store
energy in chemical form and the supercapacitors that store energy in electrostatic form.
In electric traction systems, the concept of hybrid energy storage systems is introduced
to compensate for the limits related to each storage system; the hybrid energy storage
system (HESS) is composed of batteries, supercapacitors, and full cells. The supercapacitors
are utilized to provide optimum performance in transient regimes. A summary of the
performance of technological variants of energy storage systems and energy sources are
presented in the Ragone diagram in Figure 2.
The batteries are classed as primary, secondary rechargeable, mechanical replacement,
reserve, and thermal. The charge transfer between the cathode and anode in Li-ion battery
cells is carried out by lithium ions in the electrolyte; a Li-ion battery has no metallic
Li. Therefore, commercial production cathode materials include LiCoO
2
, Li(NiCoMn)O
2
(NMC), LiMn
2
O
4
(LMO), and LiFePO
4
(LFP). Graphite is currently the most used anode
material. Researchers have been working on groupings of electrode materials that can
deliver higher voltage and higher capacity in their continual hunt for more power and
capacity. Silicon (Si) alloys are intensively pursued for the anode, with the objective of
addressing material stability and cycle life concerns. Higher voltage phosphates such as
LiMnPO
4
and LiCoPO
4
, as well as high-voltage spinel, LiMnxNi
2−x
O
4
, are of research
interest in the realm of advanced cathode materials for improved material stability and
cyclability [12].

World Electr. Veh. J. 2022,13, 65 4 of 28
Figure 2. Ragone plot of various energy sources (adapted from [13]).
2.1.3. Power Electronic Units
The power electronic integration in the EV is a cost-effective solution. It plays the
role of support to transfer and adapt energy between the energy storage system and the
drive motor. The power conveyed by the battery should guarantee the ability of the electric
motor to start the vehicle, as defined by the algorithms dedicated to the control system,
which is defined for each type of motor to ensure its operation at the ultimate efficiency,
usually between 95% and 98%. There are various control strategies accurately applied to EV
traction systems such as Adaptive Model Reference Control. Neural networks and fuzzy
logic are used with promising applications to realize the concept of intelligent controllers.
The power electronic components must be conditioned to both high temperatures and high
vibration levels [9].
Figure 3presents the principal component in the electric powertrain system, namely,
the DC/DC converter, the DC/AC inverter, the on-board charger, and other auxiliary
converters that serve to adapt the energy to power the several loads in the EV, the control
units used to manage the energy flow between the electric powertrain components.
Figure 3. Power electronics of an EV.
2.1.4. Transmission
The motor is characterized by a very high operating range (16,000 rpm on a Tesla
Model S for example) and torque quickly available at low revs, which eliminate the necessity
of a gearbox. A gear ratio reductor with single speed or at most dual speed is commonly
utilized. It should be mentioned that it is an important element to be considered while

World Electr. Veh. J. 2022,13, 65 5 of 28
studying the electric motor in the powertrain; on a Tesla Model S, the reduction ratio is
approximately 10:1, and it is generally provided by an epicycloidal gear train, which is
mainly used in automatic gearboxes.
2.1.5. Electric Motors
Electrical machines are utilized to transform electrical energy into mechanical energy
and vice versa and to provide torque and power to the driveline of the EV. The energy
conversion efficiency of an electric machine is between 80 and 96% [
9
]. The electric motor
provides high torque and high power density with better torque characteristics at the
starting phase, with an imminent rated power that is two or three times higher than the
rated power of the conventional ICE, and it is utilized in regenerative mode when braking
and decelerating for charging the storage system [9].
2.2. Pure electric Vehicle Architecture
An electric vehicle uses only electric power in the traction system. There are different
EV architectures that are achievable due to variations in the arrangement of the components
of the electric drivetrain. In this work, the presented architectures are only for pure
electric vehicles.
The components of the electric powertrain are the motor (M), differential (D), gearbox
(GB) with a clutch (C) or a fixed gear (FG). Figure 4presents the different EV architectures;
they are similar for battery electric vehicles (BEVs) and fuel cells electric vehicles (FCEVs).
Fuel cells can be either the primary or secondary energy source, depending on the require-
ments [
7
]. Figure 4a shows an electric architecture that includes an electric motor, a clutch,
a gearbox, and a differential. This architectural configuration was primarily used in the
conversion of ICE vehicles to electric vehicles using the existing components. In Figure 4b,
the clutch has been removed and replaced by the gearbox with a fixed gear architecture;
hence, the weight of the powertrain is reduced in this configuration.
Figure 4.
Different powertrain configurations of pure EVs: (
a
) primary architecture; (
b
) reduced
architecture; (
c
) modern architecture; (
d
) dual motor architecture; (
e
) in-wheel architecture; (
f
) direct
drive architecture.
The most preferred architecture by EV manufacturers in modern models is shown in
Figure 4c; it includes one electric motor with a fixed gear and a differential integrated into
a single assembly. Figure 4d presents an architecture with a dual-motor configuration in
which the differential action can be provided by the two motors; the wheels are individually
actuated by two electric motors separated via a fixed gear. They can operate at different
speeds and provide the differential features. Figure 4e presents a called in-wheel drive
configuration; this architecture incorporates a fixed epicyclic gearing system to reduce the
output speed of the motor to the appropriate speed. It offers the advantages of a high
speed reduction ratio with an in-line arrangement of input and output shafts; the compact
propulsion system requirement eliminates the use of reduction gears and mechanical
differential in the driveline by placing a direct drive motor in the exact location where
torque is required [9].

World Electr. Veh. J. 2022,13, 65 6 of 28
The arrangement of the direct drive motors as shown in Figure 4f for electric vehicles
simplifies the mechanical layout, reduces the number of driveline components, energy
loss in transmission, maintenance, and weight, and improves the overall reliability and
efficiency of the system. This gearless wheel motor drive system is used for high-torque
and low-speed applications [14,15].
The configuration of the mentioned architecture depends on the required size and
the application of the electric vehicles; many parameters are considered, essentially, the
performance, the compactness, the weight, and the cost of the EV. Nowadays, the popular
configuration is the one presented in Figure 4c; it has been broadly used in current electric
vehicles for training both wheels by using only a single motor, and the one in Figure 4b is
in second place.
The Chevrolet Spark, Nissan Leaf, Kona and Ioniq from Hyundai, and Niro from Kia
use a front-wheel drive system. However, EVs can have a rear-wheel drive framework with
a similar arrangement to the front wheel drive; the Tesla Model S, BYD E6, Reva, and E20
sport from Mahindra utilize rear-wheel drive with a single-speed transmission reducer [
9
].
Figure 5shows an all-wheel drive (AWD) architecture with an in-wheel motor (M)
and reductor (R) system. The AWD uses two motors to drive the front axles and two
motors to drive the rear axles; it provides better traction control and prevents slipping
when driving in harsh conditions. Torque orientation can be used for better cornering and
efficient driving performance [9].
Figure 5. All-wheel configuration.
3. Electric Traction Motors
The electrical machine and the power inverter are combined in a single unit to form
the core unit in electric vehicles.
3.1. Essential Characteristics of EV Traction Motors
An EV traction motor must meet different types of operating criteria than those used
in industries. In industries, most loads are constant and classified, while on the road, the EV
may need to change speed, increase torque on slopes, and abruptly apply brakes. Figure 6
shows a typical load profile that is intended for a traction motor [
4
]. It is imperative to note
that the motor exceptionally or rarely follows the torque–speed curve during operation.
These curves can be viewed as circling all load points. The full load cycle can be divided
into three sections depending on the speed, as shown in the graph of Figure 6.

World Electr. Veh. J. 2022,13, 65 7 of 28
Figure 6. Typical speed–torque characteristics of EV electric traction motors.
The main characteristics required for electrical machines for traction purposes include
quick and rapid torque response with important power density at low speeds for starting
and scaling, as well as consistent power at higher speed, high efficiency over the wide
range of speeds with constant torque and constant power, overload capacity, usually twice
the rated engine torque for short durations, small size, reduced weight, a lower moment of
inertia, acceptable cost, as well as high reliability and robustness. For different operating
conditions of the vehicle, the fault tolerance ability has to be considered [16].
The choice of an electric vehicle motor depends on the conditions outlined by the
variables as presented in Figure 7that are the mission of the vehicle, the restriction of
the vehicle, and power source variables. The vehicle restriction includes the vehicle type,
vehicle weight, payload, and battery weight. The vehicle requirement variables are defined
by a drive cycle. Considering the aforementioned variables and the characteristics that the
motor meets, the performance requirements of the electric vehicle can be chosen [9].
Figure 7. Power train interfaces.
3.2. Motor Drive Types
The electric machines integrated in electric vehicles must meet the specific characteri-
zation discussed above, especially a high efficiency, a high rated torque, a wide high-speed
range coupled with constant power, a high starting torque, high power at cruising speeds,
high specific power and power density, high overload capability, fast dynamic response,
good flux weakening capacity at high speed, a good fault tolerance characteristic, and high
reliability. These requirements are crucial for the various machine types, in addition to
the cost that must be acceptable and competitive in the market [
17
]. Figure 8presents the
potential motor types and possible choices for EV applications. The basic types of machines
used in electric vehicles (EVs) are induction machines, permanent magnet synchronous
machines (PMSMs), switched reluctance machines, synchronous reluctance machines, and
direct current machines. In the latest vehicles, four classes of motors have been adopted:
IMs, synchronous machines, PMs, and reluctance machines.

World Electr. Veh. J. 2022,13, 65 8 of 28
Figure 8. Motor types available for electric vehicles [12].
Different machine configurations have been utilized or are likely motors to be used,
including the conventional radial flux machines in addition to the axial and transverse
flux machines.
3.2.1. Permanent Magnet Synchronous (PMS) Motors
When it comes to vital productivity, the most efficient motor is the permanent magnet
(PM) brushless motor, followed by an induction motor with relatively comparable efficiency.
In fact, many vehicle manufacturers (for example, Nissan, Honda, and Toyota) have actually
used these motors. These motors have a higher power thickness and a higher competence,
as well as being more powerful in heat diffusion [
18
]. The machine takes advantage of
the high energy density of the magnets, on the grounds that the stirring of the permanent
magnet requires limited space. As no excitation current is required, the PMSM gives
immense proficiency in the field of ostensible speed. The dominant losses in the context
of PMSM are the iron losses, which occur in the stator and can be effectively reduced by
a cooling system. PMSM outperforms IM in terms of control and productivity. Its major
obstacle is the high cost of rare earth magnets such as NdFeB. Another weakness is the
extra current segment needed to debilitate the field, through which higher stator losses
occur and productivity decreases at high speed [19,20].
3.2.2. Induction Motors
Due to their low cost and robustness, induction motors are the most commonly utilized
machines in industrial applications including electric traction.
Induction motors are generally used in electric vehicles due to their important pro-
ficiency, excellent speed control, and the absence of commutation. An Induction Motor
Drive is ideally used in EV. They are generally recognized these days since they are the
least dialed switch. This explains their high reliability and maintenance-free tasks [21].
Induction motors are typically operated with a vector-control drive, which enables
a wide speed range variation. Induction machines are characterized by three distinct
operational regions, as shown in Figure 9, a constant torque region, constant power region,
and when reaching high speed, reduced power regions; these characteristics are determined
by the machine design, power electronics, and control [
7
,
17
]. It can be clearly seen that
the typical speed-torque and power characteristics are similar to the requirements of the
electrical traction system.

World Electr. Veh. J. 2022,13, 65 9 of 28
Figure 9. IM characteristics and variation of variables with speed.
3.2.3. Permanent Magnet Brushless DC Motors
The advantage of PMBLDC motors is their ability to deliver higher torque, at a similar
amount of current and voltage, compared to other motors. As these have high power and
much greater productivity, magnetic brushless DC motors have a decent ability to be used
in the EV pulse setting [
5
]. The disadvantages of the PMBLDC motor are the expensive
magnet used in the rotor. It is difficult to build large torque into the motor due to the
mechanical strength of the magnet. In addition, the weakening capacity of the field is
limited due to the presence of a permanent magnetic field. The operation of the constant
power region can only be extended by advancing the switching angle [22].
3.2.4. Switched Reluctance Motors (SRM)
Switched reluctance machines (SRMs) use rotor position switches to energize the
phase windings separated in sequence. The extension of high speed is conceivable. The
rotor aims to proceed to a place of least reluctance, thus inducing torque. SRMs possess
qualities, namely, a large starting torque and great adaptation to non-critical failure capabil-
ity, thus being reasonable for EV use. The steady-state activity is conceivably shaped by
the phase progression of current in the conduction edge of the stator to the point where
the coverage between the progressive phases occurs [
5
]. The SRM rotor is very simple as it
does not consist of any windings or brushes or commutators or magnets. Due to its simple
construction and low inertia ratio, this motor consists of high speed operation and rapid
acceleration; the main disadvantages of SRM are the torque ripple and noise [22].
3.2.5. Direct Current Motors
Excursion motors for electric vehicles are divided into two sections, switching mo-
tors and non-switching motors. Switch motors are essentially conventional DC motors,
including series and shunt excitations. DC motors have long been the subject of interest
due to the simple control and decoupling of motion and torque. DC motors are still great
candidates for low-power applications. DC brush motors can achieve high torque at low
speed, making them suitable for traction frame. However, low power density, relatively
high maintenance and commutations are the disadvantages of brushed DC motors, making
them unfit for standard electric vehicle application. On the contrary, brushless DC motors
offer better efficiency and require less maintenance [
23
]. The DC (direct current) drive
has been used evidently in EVs due to the fact that it offers perfect speed control and
torque requirements.

World Electr. Veh. J. 2022,13, 65 10 of 28
4. State of Art
4.1. Recent Trends of Electric Machines for Electric Vehicles
4.1.1. Traction Machines with Rare-Earth Magnets
The ability of the permanent magnet-based machines to develop permanent magnet
torque and reluctance torque and to achieve a wide high constant power speed range
operations has increased their appeal for traction drive systems, with their much-improved
magnetic properties when compared to non-rare-earth based magnets, which make it possi-
ble to achieve the desired performance. The rare-earth magnets are equivalent magnetically
to very high current coils (of the order of 1 kA per mm magnet thickness) with no loss
according to [
24
]. The rare earth magnetic materials, especially neodymium iron boron,
form the basis for the traction motors used in many of today’s leading electric vehicles.
These magnets enable the design of motors that offer extremely high torque densities,
making them compact and lightweight, whilst also offering high efficiencies. However,
there are several arguments that this technology may not offer the best long-term solution
for use in this application. Rare earth magnets are expensive, doubling or more the raw
material cost of the electric motor. NdFeB motors may also not be as efficient during normal
vehicle operating conditions as the headline claims may indicate, with control strategies
needed to weaken the influence of the magnets, allowing higher speed operation, but being
a source of inefficiency [5].
According to [
25
], the cross-cutting pillars of sustainability, environmental, economic,
social, and technical fields have differing conclusions regarding the use of permanent rare
earth magnet motors in the EV industry, which shows the need for the automobile industry
to come up with strict guidelines using a full life cycle assessment [25].
4.1.2. Traction Machines without Rare-Earth Magnets
A major trend in the design of machines for EVs is the parallel efforts toward non-rare
earth machine alternatives. By eliminating rare-earth magnets, not only is the motor cost
reduced, but the dependence on this critical material is removed. Induction machines (IMs),
synchronous reluctance machines (SynRMs), and switched reluctance machines (SRMs)
have had a good shot at meeting this need. The increasing demands on high specific
power and power density requirements are eliminating IMs as viable options Both SynRMs
and SRMs have a simple construction of a rotor composed of only thin steel laminations;
SRMs are characterized by consequential noise along with an important torque ripple and
vibration, in addition to high complexity and expense in the controls. SynRMs are also
attractive in terms of strength, high efficiency, low torque ripple, and simplicity of control
but represent a crucial disadvantage such as a lower power factor that impacts converter
sizing and cost and more importantly, they have a limited constant power-speed range. If
meticulously designed, SynRMs with no magnets can be very interesting and tempting
low-cost machines for both motor and inverter aspects. It seems that with more specific
and aimed research, SynRMs and SRMs can afford a path to gain high performance traction
machines without rare earth minerals.
In the paper [
26
], the authors investigated alternatives to replace rare-earth PM motors
employed in direct drive applications. The proposed motors were a surfaced PM (SPM)
motor with non-rare-earth PM, ferrite PM (Fe-PM), a spoke type motor with Fe-PM, a
synchronous reluctance motor (SynRM), and a PM-assisted SynRM (PMaSynRM). The
analyzed results of each motor were compared with the results of the reference motor. In
particular, the demagnetization phenomenon of the motors with Fe-PM was analyzed since
the Fe-PM is easily demagnetized by the reversed flux. Overall, this paper suggests the
pros and cons of each alternative to substitute rare-earth PM motors.
The new trends are about to substitute the permanent magnet in PMSM with a wound
rotor. To keep with the advantage of the synchronous machines, the most innovative
solution is the one designed by the Mahle company, and among the most powerful wound
synchronous motors are the fifth generation designed and integrated by BMW in iX M60,
iX xDrive 40, and iX xDrive 50 [27].

World Electr. Veh. J. 2022,13, 65 11 of 28
4.1.3. Machine Integration and Thermal Management Systems
Machine and power converter integration is another growing tendency that will keep
increasing. As space requirements for vehicular comfort increase, powertrain devices must
become more compact, and innovative integration techniques consequently become more
important. The EV motor’s internal temperature significantly influences its torque/power
capabilities. The dominant heat sources are located within the electric motor stator windings
and create ‘hot spots’. To keep the motor functioning properly without exceeding the
established temperature limits, thermal management design for electric vehicles is very
important in order to manage the thermal energy dissipated by the hot spot of the motor
and the other operating components [28].
The idea of assembling the electric machine and power electronic drive into one unit
affords compactness, lowered volume, ease of installation, fewer parts, and shortened
cable runs and busbars. These are considered to be attractive technical benefits along
with reduced electromagnetic interference and reduced voltage overshoots on motor drive
terminal in addition to important expense reductions. It is estimated that integrated motor
and power converters can reach 10–20% improvement in power density and a 30–40%
decrease in manufacturing and installation expenses [29].
Figure 10 shows the four major types of inverter and motor integration techniques
that exist in the literature as presented by [
29
]. The techniques comprise radial and axial
mounting approaches that consist of mounting the inverter on either the motor housing
or on the stator. In Figure 10a, the inverter is anchored on top of the housing of the motor
while it is mounted on the end shield of the motor in Figure 10c. In Figure 10b, the power
converter is mounted on the periphery of the motor stator, while it is fastened to the end of
the stator in Figure 10d. Each of these mounting techniques is characterized by benefits and
drawbacks that are presented by [
29
]. The most frequent way shown in Figure 10a provides
a simple implementation; however, it represents some limitations when it comes to reaching
high power density. In this technique, the inverter package is placed on the housing of the
motor or even on the side of the housing. Furthermore, a shared or separate cooling system
for the motor and drive can be used. Sometimes the cooling system is separate, which leads
to sub-optimal utilization of the system volume. The other approaches where the power
converters are fitted to the stator periphery lead to a better integration; however, due to
stator curvature, they do not easily provide a smooth area to fit electronic elements. The
mounting configuration and the level of integration will be dependent on the configuration
of the vehicle, including the number of motors and axles.
Figure 10.
Motor and inverter integration options: (
a
) radial housing mount; (
b
) radial stator mount;
(c) axial endplate mount; (d) axial stator mount [17].
In order to constantly improve the power density and specific power of vehicular trac-
tion drive systems, advanced thermal management systems are needed. The authors in [
30
]
presented a detailed survey that focused on cooling techniques and their computational
methods. The paper offered a complete summary of the convection techniques used in
automotive traction motors with their benefits, drawbacks, and necessities for optimizing
cooling performance for the various techniques discussed, in addition to highlighting the
cooling methods used in the traction motors of recent vehicles. Figure 11 represents thermal

World Electr. Veh. J. 2022,13, 65 12 of 28
management systems and interconnections applied for cooling power train components
and batteries in recent vehicles [31].
Figure 11. Thermal management systems of selected vehicles (adapted from [17]).
Active cooling with water glycol is common for various drive trains and except the
Chevy Spark that uses active oil cooling. It must be noted that there are different levels
of integration and correspondingly different interconnections between components. For
example, in the Tesla, the cooling is interconnected between all drive train components and
the battery. We also see a tighter integration in the second generation of the Nissan.
Leaf compared to the first. Considering the examples provided by the Tesla and the
2017 Leaf, Chevy Spark and Bolt have standalone battery heating and cooling, and BMW
has combined heating and cooling of the battery with the air-conditioning. It is obviously
expected that most of these vehicles will follow a tighter integration with a common thermal
management system interconnecting the whole drivetrain elements, which consequently
should be monitored in a permanent way using various methods such as cooler prospection
based on thermal imaging [32].
Many studies are still devoted to develop and optimize the thermal management
system. To keep the motor functioning properly without exceeding the established temper-
ature limits, a new cooling concept for PM motors based on a nonlinear tracking controller
to govern the cooling system operation was proposed by [
33
]. As a result, the stator hot-
spot temperature of the tested motor was stabilized with an average error of 0.13
◦
C and
a 68% power consumption reduction when compared to classical control. The authors
in [
34
] investigated the design optimization of a thermal management system for battery
modules, controllers, and electric motors in EVs. A combination of passive and active
cooling systems was proposed. The Design Failure Mode and Effect Analysis method has
been deployed to identify the potential failure modes and causes so that improvements
can be made for battery modules, controllers, and electric motors. The material selection
process for the designs was based on the analysis using Cambridge Engineering Selector.
It was found that the best material for the electric motor and controller water jacket is
aluminum alloy 6060 while air cooled ducting used high-density polyethylene, and battery
housing used polycyclohexylenedimethylene terephthalate.
4.2. Features of Electric Motors for Electric Vehicles
4.2.1. Power Density
Motor power density is a crucial variable when it comes to electric traction and aircraft
vehicles. Various designs to improve this characteristic in different motors is discussed in
the paper [
35
]. One can notice that motor power density has reached 0.5 kW/kg to 2 kW/kg

World Electr. Veh. J. 2022,13, 65 13 of 28
for hybrid electric vehicle applications [
36
]. The paper [
37
] presents a solution to improve
the power density of electric motors used in electric or hybrid cars using a dual motor
with a planetary transmission system. By increasing the power density, a reduced amount
of raw materials is required, and consequently, electric motors are more cost efficient.
To achieve higher power densities, a new winding type is suggested; contrary to actual
distributive windings, a fully automatic production process is possible since winding bars
can be inserted in the stator slots automatically. With these bars, the freedom of designing
the winding is increased [
38
]. This offers new possibilities to increase the power density
of electric motors. One key factor to increase the power density is to improve the thermal
conductivity of the winding. Premanufactured winding bars significantly increase the
winding design freedom since the production process allows an unrestricted placement
of single conductors that is not possible with the conventional approach. In this paper,
the influence on the thermal conductivity of one promising bar design, namely, the use of
twisted wires, is investigated [39].
4.2.2. Dynamic Response
The authors in [
40
] present some of the most common traction solutions used for
electric vehicles adopted by different car manufacturers, covering the dynamic response of
the most used electric machines applied in EV. The paper describes the behavior of three
types of electric machines used nowadays in electric commercial vehicles: a brushed direct
current machine (DC), a brushless machine (BLDC), and an induction machine (IM). The
brushed DC machine presents the important disadvantage related to its maintenance cost.
The need for brush changes after a certain period makes this very costly. Brushless machines
do not have this maintenance cost-related problem [
41
]. For the induction machine, the
cost of production and maintenance is the lowest among the three analyzed machines.
Consequently, this type of electric machine is more suitable to be used than brushed or
brushless DC machines. To compare these types of machines, they developed a testing
regime based on the experience of a driver facing all functional situations. They took into
consideration the rapid and slow start-stop regime, speed change regime, and the backward
movement of the vehicle and studied the behavior of the three types of machines using
these testing regimes. Despite their advantages and disadvantages of one versus the others,
these types of electric machines are all used nowadays in the prototypes and commercial
EV/HEVs.
The paper [
42
] presents the modeling of PMBLDCM (Permanent Magnet Brushless
DC Motor) with the load characteristics of an urban city electric car. The dynamic responses
of torque and speed of the motor in the constant torque region are discussed Tests carried
out using Matlab/Simulink in an attempt to obtain data describe the dynamic responses of
the motors that drive electric cars in cities.
Electric vehicle drive systems require fast torque response and high efficiency over a
wide range of velocities. In the paper [
43
], a fast torque response control strategy suitable
for the region above the base frequency is proposed based on an analysis of the impact of
the efficiency optimization strategy on the dynamic response. The operation characteristics
of induction motors in typical drive cycles are analyzed, and then an efficiency optimization
strategy based on the loss model and its corresponding fast torque response control strategy
is proposed. The efficiency optimization strategy improves the motor efficiency at a steady
state, and the fast torque response control strategy distributes magnetizing current and
torque current according to the voltage limit offset to achieve maximum torque output in the
dynamic process. The strategy breaks through the limitation of traditional maximum torque
control strategies based on the steady state analysis. The simulation and experimental
results indicate that the proposed control strategy can provide fast torque responses above
the base frequency in dynamic processes and reduce the impact on the electric vehicle
dynamic response caused by the efficiency optimization strategy.

World Electr. Veh. J. 2022,13, 65 14 of 28
4.2.3. Noise Level
The importance of the vibration and dynamics of electric vehicle drivetrains has in-
creased because of noise and durability concerns. In study [
44
], the important dynamic
responses of drivetrains, including the dynamic mesh force acting on the gear teeth, dy-
namic loads acting on the bearings, and torsional fluctuation of the tire or load under
major vibration excitations, such as motor torque fluctuation excitation and spiral bevel
gear mesh excitation, were investigated. The results demonstrated that at a lower motor
speed, dynamic responses such as the dynamic mesh force, dynamic bearing loads, and
dynamic torsional displacement of the tire or load under motor torque fluctuation were
dominant. At a higher motor speed, however, the dynamic responses under the gear mesh
excitation were dominant. In addition, increasing the pinion-motor torsional compliance
was an effective approach for suppressing the dynamic responses of drivetrains under
motor torque fluctuation [45].
The mounting of power converters on electric machines to form one compact package
comes with critical challenges for the resulting system. One crucial difficulty consists
of complex and augmented thermal management problems of the whole system. An
additional problem consists of the motor’s vibration: motors are more tolerant to vibration
and harshness than electronic boards that are delicate and less tolerant to vibrations.
Therefore, combining these two components in one package comes with other new and
various challenges and issues. To solve these difficulties, many studies have been conducted
in order to come up with practical and creative solutions in order to maximize the benefits
of such systems and reduce the rate of their drawbacks and problems [46].
4.2.4. Torque Ripple
As widely known, a large torque ripple is a severe problem because it can cause severe
noise vibration, reducing the riding comfort. In addition, a large source current ripple can
appear in the power supply to the inverter that drives the traction motor. This source of
current ripple is also another severe problem because large AC current may flow from
the main battery, thus decreasing the battery lifespan. The authors in [
47
] propose an
experiment with a current tracking control technique based on a pre-computed current
profile of SRMs for vehicular propulsion by eliminating the source current ripple as well as
the torque ripple. In the same context of control, the authors in [
48
] present the application
of resonant control (RC) to suppress the impact of the PM torque ripple, which aims to
reduce the vibration of a vehicle. The paper [
49
] presents a torque ripple minimization
control strategy for an inter-turn short-circuit (ITSC) fault based on the open-winding (OW)
five-phase fault-tolerant fractional slot-concentrated winding interior permanent magnet
(FTFSCW-IPM) motor drive system with common DC bus.
4.2.5. Robustness
The robustness of a motor system refers to the perturbation of its state variables or
internal parameters and the ability of the motor system to maintain its fitness in performing
a task in the presence of the perturbation. Evaluating the robustness of a system requires
a measure of task-specific fitness. Given such a measure, we can quantify the robustness
of a motor system by introducing a perturbation and comparing the performance of the
perturbed system to that of the unperturbed system. A more robust system will exhibit a
less dramatic degradation in performance in response to the perturbation than a system
that is less robust [
50
]. There is increasing attention placed on electric motors without
PM and with less winding and mechanical commutation, such as SRMs. Due to their
strong construction and low cost, SRMs are considered physically powerful candidates
for EVs [
51
]. SRMs have gained popular recognition in the EV market due to high power
density, easy construction, low cost, rigid design, fault tolerance, torque ripple control,
vibration control, and noise, and based on these properties of the special electric motors,
in [
52
], special aspects of the BLDC motors, PMSM, and SRM-based drive systems for EVs

World Electr. Veh. J. 2022,13, 65 15 of 28
are presented and reviewed, and the reasons for substitutions of permanent magnet motors
with SRM for EV applications are explained.
4.2.6. Overload Capacity
Electrical overload is caused by the excess of current passing through the motor’s
windings that breaks the limits of the rated current that the windings can bear and carry
safely and efficiently. This phenomenon is triggered by a low voltage supply that makes the
motor draw an excessive amount of current in order to maintain its torque. Other incidents
that can cause such an issue consist of excessive voltage supply and short circuits [53].
4.2.7. Fault Tolerance
The electric vehicle drive system is a multi-variable function, with a complex running
environment and changeable system, so its failure form is complicated. Due to the long
running, environmental factors, and improper manufacturing operation as well as other
reasons, the electric drive system may have various problems, and any failure could further
expand, thereby affecting the safe operation of the vehicle. Therefore, timely, reliable, and
fast detection of the failure and an appropriate fault tolerance strategy to maintain the basic
operation of electric vehicles are valued, especially for personal cars. The authors in [
54
]
proposed a new fault-tolerant rotor permanent magnet flux-switching (FT-RPMFS) motor.
The key point is its new rotor topology with the unique configuration of the auxiliary
PM (APM), located in the rotor to enhance the air-gap flux density. The authors in [
55
]
mentioned that the probability of motor failure is greater compared with that of the single
motor drive, and without proper control, the motor failure can lead to dangerous situations
such as off tracking and violent spinning of the vehicle. The authors in [
56
] demonstrated an
important correlation between the vibrations and the electrical signals, which offers a great
opportunity to minimize and predict the risks, especially thorough artificial intelligence.
4.2.8. Life Expectancy
In contrast to conventional motors, electrical motors have additional aging charac-
teristics or aging design aspects. Motor aging factors can be grouped into four classes
that describe mechanical, electrical, environmental, and thermal aspects. For instance, me-
chanical wear and fatigue of the bearings are the main cause of failures of mains-operated
standard motors [
57
]. Depending on the applied load, mechanical stresses also cause
broken rotor bars in induction machines. Modern frequency converter-driven motors face
additional electrical aging effects such as bearing currents and high electrical stresses on the
motor insulation due to voltage peaks at the motor terminal or within the motor coils [
58
].
Humidity, grease, or salts in the motor or external vibration are environmental effects that
lead to degradation and aging of the insulation system. For this reason, many traction
motors for cars are constructed using resin-casting technologies that help to protect rotor
and stator winding from environmental factors and provide more mechanical stability [
59
].
The life expectancy of an electric car motor is difficult to predict since it is dependent on so
many variables. It has been suggested that the optimum lifetime under ideal settings is
approximately 15–20 years [60].
4.2.9. Development Maturity of the Motors
According to [
61
], many studies are being conducted in order to advance motors in
hybrid and plug-in electric vehicles, with a particular focus on decreasing the dependency
rate of using rare earth materials that are mandatory for permanent magnet-based motors.
As an ultimate objective, these studies aim to reduce electric motors’ price and expenses,
size, and weight while keeping or boosting performance, efficiency, and reliability. To
meet 2022 price targets, research must reduce the cost of the motor by 50%. Many efforts
are devoted for this purpose; the authors in [
62
] and [
63
] have proposed a test bench for
developing control, diagnostic, and prognostic strategies for the electric powertrain for an
electric vehicle.

World Electr. Veh. J. 2022,13, 65 16 of 28
4.3. Comparative Methodologies
4.3.1. Multi-Criteria Decision-Making
Multi-Criteria Decision-Making (MCDM), also known as Multi-Criteria Decision
Analysis (MCDA), refers to approaches, including software, for making decisions where
various criteria (or objectives) must be analyzed and compared in order to rank or select
options [
64
]. Multicriteria Decision Making (MCDM) is defined as the combination of
three components: search, preference tradeoffs, and interactive visualization. The first
MCDM component is the act of searching through the space of potential solutions to find
the non-dominated options that comprise the Pareto set. The preference tradeoff procedure
is used to pick a single solution (or a small selection of alternatives) from the Pareto set. The
third component is an interactive visualization approach that involves the decisionmaker
in the solution refining and selection process. We concentrate on the interaction of these
three elements, Furthermore, we identify certain research difficulties that reflect gaps in
the intersection. We present a requirement framework for comparing most MCDM issues,
solutions, and performance. We concentrate on two research issues and demonstrate them
with three case studies in power management [
65
], financial portfolio rebalancing, and air
traffic planning [66].
4.3.2. Analytical Hierarchical Process (AHP)
Selecting the appropriate option in the tender assessment process is one of the most
important concerns in every business that influences its economic existence. This would
result in a profit and general success for both the firm and its employees. Aside from
that, all benefits and drawbacks (pros and cons) of any economic offer must be weighed
in order to make the best option. Frequently, the characteristics that characterize the
economic offer are linked in a complicated manner. As a result, the decision-making
process is extremely difficult, particularly in determining which criteria are more essential
than others. The Analytical Hierarchical Process (AHP) technique, which has a strong
mathematical foundation, might be used to find a good solution to this problem [
67
]. This
strategy is used effectively (as demonstrated in this work) to evaluate excellent economic
offers and pick the best bid when acquiring computer equipment [68].
4.3.3. Analytical Network Process (ANP)
To analyze and evaluate the overall relative merits of dimensions and criteria, the
analytical network process (ANP) outperforms the analytical hierarchy process (AHP). As
a result, the WFD program is a multiple-criteria decision-making (MCDM) challenge. Al-
though the analytic hierarchy process (AHP) developed in the 1970s is designed to deal with
intuitive, rational, and irrational problems when making multi-objective, multi-criterion,
and multi-actor decisions, with or without certainty, for any number of alternatives, the
basic assumption of AHP is the condition of functional independence of the hierarchy’s
upper portion, or groupings, from all its lower parts, as well as from the criteria or items in
each level [69].
4.3.4. TOPSIS
TOPSIS is a technique. TOPSIS was founded on the essential notion that the optimal
solution is the one that is closest to the positive ideal solution and the one that is farthest
away from the negative ideal solution. Alternatives are graded using an overall index
based on their distances from the optimal solutions [70].
4.3.5. Data Envelopment Analysis (DEA)
Data envelopment analysis (DEA) is a nonparametric approach for calculating the
relative efficiency of reducing carbon emissions within a set of homogeneous decision-
making units (DMUs) with various inputs and outputs. DMUs in this context might be
businesses, schools, hospitals, stores, bank offices, and so on [71].

World Electr. Veh. J. 2022,13, 65 17 of 28
4.3.6. Fuzzy Decision Making (FDM)
Fuzzy decision making is a set of single and multicriteria strategies for picking the best
choice in the presence of imprecise, incomplete, and ambiguous data. The categorization is
based on the following new fuzzy set extensions: Types of fuzzy sets include intuitionistic,
hesitant, and type-2 fuzzy sets [72].
4.3.7. VIKOR
The VIKOR approach was created to optimize complicated systems using several
criteria. It generates a compromised ranking list and compromised solution using the
original (specified) weights. In the presence of competing criteria, this strategy focuses
on ranking and selecting among a group of options. It presents the multi-criteria ranking
index, which is based on a specific measure of “closeness” to the “ideal” answer [73].
4.3.8. DEMETAL
DEMATEL (decision making trial and evaluation laboratory) is regarded as an excel-
lent approach for identifying cause–effect chain components of a complicated system. Its
main concern consists of examining interdependent interactions between components and
identifying the crucial and important interactions using a visual structural model [74].
4.3.9. Delphi
The Delphi method is a technique that involves polling a panel of experts to arrive at
a group opinion or conclusion. Experts complete many rounds of questionnaires, and the
results are pooled and distributed to the group at the end of each cycle [75].
5. Trends of Electric Motors in Electric Vehicles
5.1. Pure electric Vehicle Development
In 2020, there were more than 370 electric car models available worldwide, up 40%
from 2019. China has the most opportunities, owing to its less concentrated automotive
industry and the fact that it is the world’s largest EV market. However, Europe has the
most important expansion of model number, since it more than quadrupled by 2020. In
all locations, BEV models are available in most vehicle classes; PHEVs are biased towards
bigger vehicle categories. In all markets, sport utility vehicle (SUV) types constitute almost
50% of the electric car models available. China has about double the number of electric
car models as the European Union, which has more than twice as many as the United
States. This disparity can be partially explained by the US electric vehicle economy’s lower
maturity, which reflects the country’s relatively weak national laws and incentives.
Figure 12 shows that the average range of BEVs has been increasing in recent years.
A new battery electric car’s weighted average range in 2020 was around 350 km, up from
200 km in 2015. Because China has a larger number of tiny urban electric cars, the weighted
average range of electric cars in the US is higher than that in China. Over the last five years,
the average electric range of PHEVs has stayed relatively steady at around 50 km.

World Electr. Veh. J. 2022,13, 65 18 of 28
Figure 12. Electric car models available globally and the average range, 2015–2022 [76].
5.2. Electric Motors in Electric Vehicles
Table 1presents some applications of different motors in electric vehicles for various
car manufacturers. The vast majority of the electric car market using a permanent magnet
motor; the percentage reached 77% by the beginning of 2021, followed by the induction
machine that reached 17% in the same period. However, the wound rotor motors are
increasing and have reached 6%. The application of DC motors is nowadays undesirable;
therefore, SRM has a lower adoption rate [9,77].
Mahle has developed a revolutionary no-magnet and non-brushed wound rotor syn-
chronous machine based on a wireless transmitter that serves as the key component of
the system. To produce energy for the rotor, it uses an alternating field, which is then
transformed into direct current for the magnet coils. The innovative machine combines
the best points of several motor designs by providing good efficiency across both higher
and lower torque levels. Overall, according to the manufacturer, the machine reaches a
minimum 95% efficiency under normal EV usage and exceeds 96% efficiency at many
operating points. There are no magnets in the fifth generation BMW motor. It functions
as a three-phase alternating current synchronous motor, with brushes and a commutator
to deliver power to the rotor windings. The special design of the current-energized syn-
chronous machine concept allows the electric motor of the BMW iX M60 to attain a very
high-power density 2.59 kw/kg; the drive unit is six-phase and contains a double inverter,
allowing for a large increase in peak power, as well as making it available at high speeds
and enabling conventional power delivery at high efficiency, reaching 93% [27].
For different electric car brands associated with the motor of each one, an overview of
motor performance values regarding power, speed, and torque is shown in
Figures 13 and 14
,
showing nominal speed (often referred to as base speed) versus peak torque. It can be seen
that the typical rated speed range is between 2500 rpm and 6000 rpm with typical peak
torque values of 150 Nm to 450 Nm for some of the different existing EVs. It should be
noted that the majority of the models cited are equipped with the PMSM.

World Electr. Veh. J. 2022,13, 65 19 of 28
Table 1. Existing motors in electric vehicles.
Drives Types Year DC SRM IM PMSM PMBLDC WRSM
Berlingo Electric 2005 X
Panda Elettra 1998 X
Reva G-Wiz DC 2013 X
Tesla Roadster sport 2018 X
Tesla Model S 2020 X
BMW Mini E 2019 X
Renault Twizy cargo 2018 X
Audi A3 e-tron 2014 X
Audi e-tron 55 quatro 2019 X X
Audi e-tron GT 2021 X
Tesla model Y (PMSRM) 2020 X
Nidec prototype 2013 X
Jaguar I-Pace 2019 X
BMW i3 2013 X
Fiat 500e 2013 X
Fiat 500e 2020 X
Focus Electric 2018 X
Mitsubishi i-MiEV ES 2010 X
Peugeot iOn 2014 X
Smart for two electric drive 2020 X
Hyundai IONIQ 2021 X
Model 3 2017 X
Prius 2017 X
Bolt 2016 X
Lexus UX 300e 2020 X
KIA e-soul 2020 X
Citroën C-Zero 2011 X
Citroën AMI 2020 X
Nissan leaf 2010 X
Mahle motors 2021 X
BMW iX M60 2022 X
Volkswagen iD.3 2019 X
Three-wheel electric tuk-tuks X
Some Chinese electric cars X
Figure 13. Maximum speed over peak power overview for the investigated motors [24].

World Electr. Veh. J. 2022,13, 65 20 of 28
Figure 14. Nominal speed over peak torque overview for the investigated motors [24].
Figure 13 shows the maximum motors speed versus peak power to compare the
maximum motor ratings. It can be noticed that the arrangement of the motors in this figure
is different from that in Figure 14. This is due to the different constant power–speed ranges
and therefore the different field weakening capacities of the motors. It also shows that even
for motors of similar peak power, the torque-to-speed characteristic can vary considerably.
6. Multi-Criteria Comparison of Electric Machines for Traction Systems
In this section, we analyze and evaluate five types of electric motors for electric vehicle
applications based on various paradigms, The criteria are determined from the factors
below. They are divided into those that have an impact on the performance, reliability, and
efficiency of the model:
•Performance: This is the set of actions that each motor can perform as a task.
•
Reliability: the reliability factor is based on the faithfulness of the motor, which is its
immunity against rapid breakdowns and supports continuous operation without any
regular maintenance.
•
Efficiency: this factor determines the capacity of the model to be more efficient with
a minimum of resources relating to power sources and electronic systems; electric
motor efficiency provides a connection between the electrical and mechanical yield.
The electric motor is generally supposed to operate at maximal efficiency at the
measured output.
These are the main factors that we used to compare the five chosen electric motors;
moreover, there are many other criteria, as presented in the radar graphs in Figures below,
mainly those impacting the maintenance and the robustness of the motors, in addition to
the first introduced ones related more to the inner characteristics, the energetic performance,
and the technical specification.
Figures 15–17 present a comparison of electric motors for EVs dependent on the
boundary specification parameters of ongoing vehicles gathered from various sources; a
higher score indicates a better element based on the criteria cited in the graphs and by
scoring each motor type. The first score relates to the induction machine due to its high
reliability, maturity, stability, fault tolerance capacity, and its low cost and maintenance,
followed by the PMSM, the PMBLDC, and then the SRM because of the torque ripple, high
noise level, and the poor dynamic response and overload capacity. The last classification
pertained to DC motors, but this classification does not mean the IM is better than the
PMSM for the electric traction application.

World Electr. Veh. J. 2022,13, 65 21 of 28
Figure 15. Factors related to the operational performance of the electric motors for electric vehicles.
Figure 16. Factors related to the reliability of the electric motors for electric vehicles.

World Electr. Veh. J. 2022,13, 65 22 of 28
Figure 17. Factors related to the efficiency of electric motors for electric vehicles.
Even though insight can be obtained by comparing data, it is not easy without consid-
ering the design, the architecture of the vehicle’s traction system, and/or the hybridization
strategy. Some vehicles use two machines while others use only one; in addition, the
motors are different in several ways. It is therefore difficult to significantly compare these
machines; nonetheless, it is informative and instructive to note some trends, notably the
shift from induction (IM) machines to the permanent magnet (PM) machines for the ma-
jority of traction applications. However, there are many more types of machines that
can potentially be applied in electric vehicles, especially a swished reluctance machine
(SRM) and synchronous reluctance machine (SRPM) as in the Tesla model 3. To establish a
correlation between different electric motors utilized in electric cars by manufacturers and
factors considered to choose one of the motors that are best for them, an observation was
made of the specific parameters, especially the internal performance criteria and the factors
related to the robustness, maintenance, fault tolerance, and environment
While the comparative research characteristics for electric motors can be instructive,
the ranking is less evident when considering the function of electronic components, power
sources, and intelligent control and diagnostic procedures in the improvement of the
targeted variables. As a result, comparing these models in a meaningful way is difficult.
Nonetheless, examining some tendencies is informative, such as the application fields, the
type, the application domain, the wanted objectives, and the preferred factors that the
electric vehicles are intended to fulfil.
Establishing a correlation between these different criteria and the factors considered
is necessary in order to choose the appropriate model that is most suitable. Among the
multi-criteria decision support methods, we used the AHP (Analytic Hierarchy Process)
method, where the criteria can be weighted by coefficients or weights, arriving at a justified
choice of comparison. Table 2presents the weighted result of the comparison criteria
(Efficiency, Reliability, and Performance), where the motor evaluation equation (MEE) is as
follows (1):
MEE = 0.539 ×Efficiency + 0.297 ×Reliability + 0.163 ×Performance (1)

World Electr. Veh. J. 2022,13, 65 23 of 28
Table 2. AHP comparison matrix of the factors related to motors in electric vehicles.
Efficiency Reliability Performance Efficiency Reliability Performance Σ Σ/3
Efficiency 1 2 3 0.55 0.57 0.50 1.62 0.5390
Reliability 0.5 1 2 0.27 0.29 0.33 0.89 0.2973
Performance 0.33 0.5 1 0.18 0.14 0.17 0.49 0.1638
Σ=1.83 3.50 6.00 1.00 1.00 1.00 3.00 1.00
In the same way, the weights of the factors of each criterion are calculated, whose
Equations are (2)–(4), Figure 18 shows all of the aforementioned comparison results.
Figure 18. Factors related to the efficiency of electric motors for electric vehicles.
Efficiency = 0.350 ×Cont + 0.237 ×C + 0.158 ×MC + 0.010 ×Sz + 0.069 ×PS + 0.046 ×W + 0.031 ×TM (2)
Reliability = 0.326 ×Rob + 0.227 ×OC + 0.156 ×FTC + 0.107 ×M + 0.073 ×L + 0.049 ×Mat + 0.034 ×Com + 0.024 ×S (3)
Performance = 0.326 ×PD + 0.227 ×DR + 0.156 ×TR + 0.107 ×MS + 0.073 ×MT+ 0.049 ×SR + 0.034 ×NL + 0.024 ×Acc (4)
Figure 19 shows the general comparison of the motors based on our case study that
prioritizes the criteria shown by Equation (1). The relative ratings show the associated
highlights below:
•
IM yields productivity higher than 91%, has extreme fidelity, low power density, and
average acceleration. IMs are among the most preferred motors by EV makers. The
high-efficiency zone for an induction machine is between the high-efficiency areas of a
PMSM and an SRM, which predicate that IMs could be favorable for a wide range of
driving cycles [3].
•
Synchronous machines have greater proficiency at lower accelerations and enhance
battery usage and propulsive extent. A synchronous motor is favored wherever steady
torque is needed.
•
BLDC motors have advanced power density, high productivity, and a small size, but
up-keep costs and controller expenses are huge.
•
SRMs are an interesting option due to the low cost of the motor/controller ensem-
ble compared to other solutions, the good reliability, efficiency, and internal failure
tolerance capacity.
•
DC motors are less difficult to control and provide high torque at curtailed speeds but
have major support costs, an expansive structure, and deficient efficacy.

World Electr. Veh. J. 2022,13, 65 24 of 28
Figure 19. Global results of the motor type’s classification.
7. Conclusions
Based on the discussion and study above, a comparison of the required attributes of
the different utilized motors in electric vehicles is provided. The basic elements that can be
drawn from this discussion are from the first comparison, in terms of performance, cost,
and energy efficiency, the most adequate machines are induction motors and PM brushless
motors. Induction motors are the best. DC motors are among the most developed inno-
vations, as much research has been done on them over the years, but they are abandoned
for the application in light vehicles; for heavy duty vehicles, there is a migration to the
AC motors after a long domination. Considering the factors related to maintenance, IM,
PMSM, and SRM present a solid advance and require minimal maintenance; therefore, DC
motors are at the bottom of the classification. Figure 19 shows the global results of the
motor type classification considering the efficiency and the maintenance factors from the
aforementioned comparisons.
The paper gives an overview of the selection of an electric motor type for suitable
electric traction application and establishes that the choice or the design of the topology of
electrical machines for electric traction applications is often a complex issue that must be
decided considering the science involved, namely, electromagnetic, mechanical, thermal,
and power electronics.
To extend this work, a desktop application is under development, where the goal is to
select the best motor fit of the electric vehicle. The user will be able to choose to include
different criteria, for example, motor composition type, thermal system, noise level and son
on; some of these criteria will be mandatory in order to select the best choice effectively.
The application will take into consideration the use of the electric vehicle, for example,
urban uses, industrial cases, and the distance per day, because each case study is related to
other selection algorithms with different criteria classification priorities.
The requirements of the electric vehicle will be mandatory in the selection, for example,
weight, speed, acceleration, autonomy, and other requirements. After entering all needed
data, the user can choose if the motor will be selected from a database where he/she will be
asked to enter more information, for example, the range of weight, volume, power, voltage,
current and yield, or the user can enter the characteristics of motors manually without
using the motor’s database. After clicking on result, radar and bar graphs are generated
base on the entered data and selected criteria, and the application also suggests the best fit
of the motor for the case use selected.
Author Contributions:
Conceptualization, H.E.H., M.Z. and A.C.; methodology, H.E.H., M.Z. and
A.C.; validation, H.E.H., M.Z. and A.C.; formal analysis, H.E.H.; investigation, H.E.H., M.Z. and A.C.;
resources, H.E.H., M.Z. and A.C.; data curation, H.E.H.; writing—original draft preparation, H.E.H.,
N.G. and A.C.; writing—review and editing H.E.H., O.L., N.G. and A.C.; visualization, H.E.H.,
M.Z. and A.C.; supervision, H.E.H., M.Z. and A.C.; project administration, H.E.H., O.L. and A.C.;

World Electr. Veh. J. 2022,13, 65 25 of 28
funding acquisition, H.E.H. and A.C. All authors have read and agreed to the published version of
the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
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