Keywords

3.1 Introduction

Currently, there are many different types of electric vehicles that have been designed and constructed [7, 8, 19]. Different electrical machine types must be investigated so that one can determine what type will be appropriate for the specific vehicle under consideration (car, aircraft, ship or train). Since the requirements will differ from one vehicle to the next, the present chapter focuses on a comparison of different machine types for each type of vehicle.

First, the objects of comparison, vehicles (hybrid and electric) and traction electric motors (TEMs) are explained. We then discuss the ultimate results of the process of selection of the most appropriate motor for the vehicle being considered and draw conclusions as to the usability of the methodology.

The two-step selection of the optimal type of traction electric motor consists of preliminary and final levels of evaluation. First, a rough estimate is made and the two best options are selected. In the final level of evaluation, the most suitable motor is selected.

3.2 Electric Vehicles

The electrification of different types of vehicles is widely discussed today because of the many benefits involved, such as:

  • reduced emissions;

  • increased operational efficiency;

  • reduced energy consumption;

  • increased reliability and fault tolerance;

  • simplified control;

  • reduced airport noise;

  • simplified autonomous implementation.

What type of traction electric motor is best suited for the electric propulsion system of a vehicle? Unfortunately, the best, optimal solution for all types of transport does not exist yet. Therefore, for each type of transport vehicle, this task must be solved individually. The optimal type of traction electric motor will depend on the specific vehicle type, on their operating conditions and parameters and on their unique requirements and limitations. A large number of different parameters should be considered for solving the multifactor optimization problem . This can be done only through a systematic approach. The features of certain types of electrified vehicles are briefly considered below.

3.2.1 Aircraft

This category of vehicle includes airplanes (international carriers, regional planes, special purpose aircraft, piloted and pilotless aircraft, etc.) as well as helicopters (from heavy to light types, piloted and pilotless, etc.). At the same time, if we are focusing on airplanes, step-by-step electrification must be envisaged (from the hybrid version to the fully electric version); for helicopters, due to their limited space, the full electrical version must be considered.

The specific operational modes of the helicopter, in contrast with the airplane, require more power and a higher energy density in the traction drive, and there is thus a need to install a more powerful electric traction motor with a larger capacity electric energy source or energy storage. We must also take into consideration the maximum takeoff weight (MTOW) of the helicopter and the space for the installation of the electric traction drive components. Thus, it is necessary to consider the following features of helicopter operation:

  • low autonomy and, accordingly, short duration flights;

  • lack of structural redundancy;

  • inability to repair during flight;

  • the most stringent restrictions on weight and fault tolerance.

Thus, the correct choice of the optimal type of helicopter traction electric motor is a highly important task, the solution of which will be considered in the following sections.

3.2.2 Cars

During our investigations, the following features of the operation of passenger hybrid/electric cars were taken into account:

  • small average annual mileage of the car;

  • low value of average utilization rate;

  • lack/partial availability of structural redundancy;

  • relatively rigid restrictions on weight and dimensions of the traction drive;

  • possibility of correcting small malfunctions during operations;

  • high maintainability and accordingly a relatively high availability factor.

It should be noted that in this chapter, in the category of cars, the features of truck and bus operations were not considered.

3.2.3 Ships

Given the specific operational conditions of ships , the following features were taken into account for the design of their electric propulsion systems:

  • high autonomy of the ship’s operations;

  • availability of structural and functional redundancy;

  • high value of the rate of technical use;

  • high maintainability of electric propulsion system;

  • possibility of repairs during operations;

  • high survivability of the propulsion system;

  • absence of tight restrictions on the weight and dimensions of the traction drive.

3.2.4 Trains

In studying the specific characteristics of this mode of vehicle, the following features of its operations were taken into account:

  • limited autonomy of operations;

  • availability of structural redundancy;

  • high coefficient of technical use and running time;

  • relatively high maintainability of the propulsion system;

  • possibility of minor repairs during operations;

  • absence of tight restrictions on the weight and dimensions of the traction drive.

3.3 Traction Electric Motors

This section provides an overview of the types of machines we compared. The different electrical machines are briefly described in terms of properties, special features, and technical data.

For the comparative analysis, the following machines were taken into account: the induction machine (IM), the switched reluctance machine (SRM) and the synchronous machine (SM), including the permanent magnet SM with distributed windings (PSM-d) and the permanent magnet SM with concentrated windings (PSM-c). Figure 3.1 presents the possible realizations for each machine type [28].

Fig. 3.1
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Cross sections of different electrical machines: a induction machine, b switched reluctance machine , c synchronous machine with permanent magnets

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3.3.1 Induction Machine

The cross section of an induction machine is shown in Fig. 3.1a. The main advantage of induction machines is high availability and relatively low maintenance cost [28]. Induction machines produce a low level of noise or vibrations compared to other machine types, the production cost is relatively low and the ability to operate in hostile environments is high. However, the power operation is limited, i.e., efficiency decreases at lower speeds and the power decreases at higher speeds. In addition, the induction motor is almost impossible to partition, i.e., it is almost impossible to divide one powerful machine into several low-power ones, because it is impossible to make unconnected stator phases that will be controlled by a separate electric converter completely independent of the others. Therefore, to ensure the high power of the induction motor’s converter, it is necessary to increase its voltage, that is, to use a high-voltage converter. In the case of sectioned electric drives, it is advisable to take a low-voltage converter with a relatively small nominal current and supply the necessary amount of submodules; in the case of traction drives with an induction motor, there should be only one electric converter.

3.3.2 Switched Reluctance Machine

The cross section of the switched reluctance machine (SRM) is presented in Fig. 3.1b. It includes the typical rotor without excitation coils or permanent magnets (PM) in the rotor. Some of the advantages of the SRM are low maintenance and low production cost, as there is no excitation needed in the rotor. Consequently, rotor losses are minimized. Moreover, the control is simple and the reliability is high compared to other machines. In addition, the SRM provides thermal stability and has a relatively high overload capability.

Due to the simplicity of the design, this kind of motor turns out to be cheaper than the classic induction motor. In addition, the SRM is easy to make in multi-phase and multi-section versions, where we divide the control of one motor into several independent converter submodules working in parallel. We can thus increase the reliability of the motor drive; thus, for example, the failure of one electric converter will not lead to the total failure of the whole electric drive, and the remaining submodules will work for a while with a slight overload.

However, the SRM has high torque ripples and therefore an increased generation of noise and vibrations. Due to the specific design of the motor and the impulse nature of the current, it is difficult to obtain a stable torque, and as a rule, the torque in the SRM pulsates. That feature limits the applicability of this motor type for vehicular traction drives. In addition, the pulsating nature of the traction torque has a negative effect on the lifetime of the motor bearings. This problem can be partially solved through a special profiling of the shape of the phase current, as well as through an increase in the number of phases. As discussed in [22], these machines are limited if we need torque at low speeds, because of the factor of saturation.

3.3.3 Permanent Magnet Synchronous Machine

The cross section of the synchronous machine (SM) is shown in Fig. 3.1c. It is realized as a PSM with a surface PM. Permanent magnets provide the necessary magnetization of the rotor without corresponding losses, and that feature increases the efficiency of this type of motor in comparison with inductive ones. Since expensive rare-earth metals are required for the production of magnets, until now the price of such engines has been quite high and demand has been higher than supply. Nevertheless, in recent years, with the increase in PSM production, there has been a significant decline in prices.

Compared to all the other machine types, the PSM has high power density and a high level of efficiency around the nominal speed. Additionally, due to the missing rotor windings, there are no copper losses; thus, less cooling is required [22, 28]. A PSM can be implemented in a smaller volume for the same speed and power than an SRM [22]. Due to the use of rare earths, the price is high and this is an important factor considering the PSM, even though it is not very decisive for some applications. Distributed and concentrated windings in the PSM have been taken into account for the comparison.

The PSM is optimal for cases where a large control range is not required. For example, such a kind of motor is ideal for drives with a fan load characteristic. In that version of the PSM application, the rotation speed changes are relatively small, with a maximum of two speed changes, because the airflow is weakened in proportion to the square of the speed.

The disadvantages of this type of motor include the risk of demagnetization at high temperatures, a situation that, however, is rarely encountered in practice. In addition, the problems associated with motor repairs must be taken into account. There are two primary problems: There are strong magnets in the rotor and the process of extracting the rotor from the stator is complex and requires the use of special tools.

The abovementioned characteristics of electrical machines complicate the selection of a suitable machine, due to the high complexity and interdependence of parameters and the mixed advantages and disadvantages. The following sections introduce the parameters for a preliminary comparative analysis.

3.4 First Step—A Preliminary Comparative Analysis

Ten parameters, used in the comparison, will be mentioned and briefly explained in this section. Each parameter has a certain influence on a system’s behavior and hence has to be considered. Furthermore, the priority of parameters can differ from one application to another. Therefore, parameters have to be weighted in order to meet the different requirements for different applications.

3.4.1 Parameter Identification

The main goal of the applications is to transport persons or cargo, and the transport has to provide safety, usability, and efficient operations. Therefore, the indicators for comparative evaluation must take into account the requirements and conditions for the future operation of the applications. Additionally, the complexity, cost, and maintainability of the system play an important role for the manufacturer. Furthermore, the parameters need to be independent, not correlating with each other, since a correlation of parameters will shift the results. Only the lower limits of values as determined by considerations and calculations and as noted in existing publications were taken into account for evaluation.

Thus, the pre-design is supposed to meet the requirements even though at an early stage of a design process some effects might not be considered yet. In some cases, adequate assumptions have to be made. The abovementioned procedure leads to the following parameters:

  • efficiency,

  • power density ,

  • Mean Time to Failure (MTTF) ,

  • Mean Time to Repair (MTTR) ,

  • reparability,

  • fault tolerance ,

  • noise,

  • volume,

  • complexity,

  • cost.

3.4.2 Determination of Parameters

In this section, the determination of parameters will be shown in order to provide an example for the evaluation of reliability and fault tolerance.

3.4.2.1 Reliability

For aircraft applications, the reliability and fault tolerance of the main electric motors are extremely important characteristics of electrical machines and are often decisive considerations. In other words, reliability and safety define the design features and the structural connections of electrical drive trains.

Therefore, the most accurate comparative analysis and evaluation of reliability indices at the design stage of various electrical machines, which are a part of the electrical drive train and which take into account future operating conditions, can be considered an important problem. The main faults in electric machines can be classified as in [27]:

  • stator winding faults;

  • broken rotor bar or end-ring faults on the IM;

  • static/dynamic air gap irregularities (rotor eccentricity);

  • bearing failures;

  • defects of the permanent magnets of the PSM.

Each fault disrupts the motor’s normal operations, producing several symptoms, such as unbalanced line currents and air gap voltages, torque and speed pulsations, decreased efficiency and lower torque, excessive heating, and increased losses. The operating experience of electrical machines indicates that the most vulnerable elements of electrical machines are the stator windings and the bearings [15, 20, 21]. Statistical data on failures in various parts of electric machines is shown in Fig. 3.2.

Fig. 3.2
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Statistical data on failures in various parts of electric machines

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Considering the above data charts, the failure rate of electric machines λ EM can generally be determined by the expression:

$$\lambda_{EM} \left( t \right) = \lambda_{S} \left( t \right) + \lambda_{R} \left( t \right) + \lambda_{B} \left( t \right).$$
(3.1)

where λ S , λ R , and λ B are the failure rates of parts of the electrical machine (stator, rotor and bearing) respectively. The probability of failure-free operations of the system is defined as:

$$P_{EM} \left( t \right) = e^{{ - \left( {\lambda_{SO} + \lambda_{RO} + \lambda_{BO} } \right)t}}$$
(3.2)

where λ SO , λ RO , and λ BO are the failure rates of the main parts of electrical machines, which are calculated considering defined operating conditions with correction factors k i , i = 1, … m for each operational mode:

$$\lambda_{SO} \left( t \right) = \ {\lambda}_{Sm} \sum\limits_{i = 1}^{m} {k_{i} t_{i} } /t$$
(3.3)
$$\lambda_{RO} \left( t \right) = \lambda_{Rm} \sum\limits_{i = 1}^{m} {k_{i} t_{i} } /t$$
(3.4)
$$\lambda_{BO} \left( t \right) = \lambda_{Bm} \sum\limits_{i = 1}^{m} {k_{i} t_{i} } /t,$$
(3.5)

where λ Sm , λ Rm , and λ Bm are the mean values of the failure rates of every part of electric machines in “ideal” laboratory conditions and t i , i = 1, …, m are the durations of each mode of operation.

Based on statistical data, we estimated the reliability indices for the IM, SRM and PSM, with a given level of power (600 kW) and a given rotational speed (400 rpm). Table 3.1 summarizes the calculated values for various prediction intervals. Those results are presented graphically in Fig. 3.3.

Table 3.1 Reliability values for various machine types
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Fig. 3.3
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Reliability functions of the IM, SRM and PSM

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3.4.2.2 Fault Tolerance

To evaluate the level of fault tolerance of the traction motor for an electrical helicopter, three characteristics of electric machines, which have a major impact on its functioning in fail operation mode, were analyzed:

  • overload capacity;

  • partial load operational mode;

  • torque ripples in case of failure.

During the normal (failure-free) operational mode, the electric motor can endure a short-term overload because its thermal capacity is sufficiently large. In failure cases, the situation changes dramatically.

The largest number of fail operational modes are caused by technological electric overloads. The consequences of an overload are the overcurrent and overheating of the electrical machine , which leads to a reduction of the reliability indices of the motor and a decrease of its lifetime, as can be seen in Fig. 3.4 [4].

Fig. 3.4
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Overheating influence on the lifetime of the components of an electric drive

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For the traction motor of the electrical helicopter, considering the tight requirements of drive reliability and fault tolerance, the overload capability in fail operational modes is especially important. In such operating conditions it is also extremely important to be able to operate the helicopter stably especially during operational modes of significantly reduced power without undue asymmetry of motor parameters.

For a comparative evaluation of this parameter, a qualitative analysis of torque ripples was carried out for fail operational modes. The estimation range is from 1 to 10, the maximum value of 10 representing the best option. Taking into consideration collected data and the results of calculations [3, 11, 18], Table 3.2 presents a comparison of fault tolerance indices for the selected motor types.

Table 3.2 Comparative analysis of fault tolerance
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3.4.2.3 Priority Coefficient

Weighting factors are needed in order to assure an appropriate evaluation of each application. Parameters are weighted roughly through priorities, which can be seen in Table 3.3. In addition to these pre-evaluated priorities, the priority coefficients K p are determined and are presented in Tables 3.4, 3.5, 3.6 and 3.7.

Table 3.3 Weighting factors for different vehicle types
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Table 3.4 Electrical machine types for aircraft application
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Table 3.5 Electrical machine types in automotive application
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Table 3.6 Electrical machine types in maritime application (ships)
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Table 3.7 Electrical machine types in railway application
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The factors are derived from literature research, expert knowledge, and scientists’ experience. As aforementioned, safety, usability and efficient operations are decisive factors regarding the electrical drive train. Therefore, parameter efficiency, MTTF, MTTR, reparability, and fault tolerance get the highest priority coefficient.

3.5 Results of the First Step for Various Vehicular Applications

In this section, examples are given of the applications of electric aircraft, electric cars, electric ships, and electric trains and a comparison is made of the different machine types for each application in terms of parameters and the determination of priority coefficients.

3.5.1 Electric Aircrafts

Electric aircraft means fully electrified aircraft with direct drive and no gear box. Since weight plays an important role and a gear box usually accounts for a high percentage of weight as far as the drive train is concerned, these machines are characterized as low speed and high torque machines.

Furthermore, reliability, fault tolerance, and power density have to be treated as highly important factors. That is the reason why the PSM is considered to be the best choice for aircraft, as can be seen in Table 3.4. Cost and complexity are not important in the current investigation stage. Up to now there have been feasibility studies for aircraft, and the provision of safety, efficiency and power density is considered to be increasingly important [2, 23, 26].

3.5.2 Electric Cars

The results presented in Table 3.5 indicate that, for the automotive application, i.e., electric cars, different types of electrical machines can be used. Considering the car companies around the world, many European, American and Japanese companies use a PSM for hybrid electric cars, but some companies prefer the IM or SRM [22]. Figure 3.5 shows the distribution of the use of electrical machines in hybrid cars. The distribution of the relative weighting factor, which is more or less equal, is presented in Table 3.5. This means that the choice of the appropriate machine can depend on other factors, such as production knowhow, political aspects, and so on [12].

Fig. 3.5
figure 5

Distribution of the use of electrical machines in hybrid electric cars

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3.5.3 Electric Ships

The traction electric motors of ships are characterized by high power (over 1,000 kW) and a low rotational speed of the propeller shaft. Stringent requirements regarding the fault tolerance of the main traction motor are imposed for certain (but not for all) operational modes: passage through straits, channels, and other narrow waterways, in areas with difficult navigation conditions and in harsh weather and ice conditions. However, considering the less rigid requirements for dimensional characteristics (volume and weight), compared with aircraft equipment, there is significant potential for implementing structural and functional redundancy. Taking into account the fact that fuel cost accounts for 70% of ship operating expenditures, the efficiency of the motor is a highly important consideration [6]. Hence, the most promising machine types for marine electric propulsion systems are the PSM (e.g., produced by ABB) and the IM (manufactured by Siemens), see Table 3.6.

3.5.4 Electric Trains

Considering the modes of operation, design features and technical parameters of electric drive trains, the requirements for railway application lie between the automotive and the maritime applications. The power of the single traction electric motor is usually less than 1,000 kW and the rotational speed (without gears) is between 2,000 and 3,000 rpm. The requirements for weight, volume, size, and noise characteristics are more stringent than the requirements imposed on a ship’s traction motors. At the same time, they are less stringent, in comparison with cars. Using a multi-aggregate scheme of the railway’s electric propulsion, in which every locomotive with a motor (or motors) is a practically independent propulsion unit, we can minimize time and cost to implement an optimal maintenance strategy with the required level of redundancy and, accordingly, the required degree of fault tolerance.

The data presented in Table 3.7 shows that, despite the rather close total values of the complex index, the PSM has an advantage over the IM and the SRM. Nevertheless, today the PSM (Alstom) and the IM (Siemens) are used as traction motors. Also Japanese companies produce electric railway vehicles with the PSM and the IM [14].

Thus, the main challenge in selecting the most optimal type of traction motor has not yet been completely solved, and the developers often base themselves on their own experience in the design of electric motors.

For the second step in the comparative analysis, we propose a method of refined analysis, considered below, for the main traction motor of a ship’s electric propulsion system.

3.6 Second Step—Comparative Analysis

The main disadvantage of existing methods for the choice of the optimal traction motor for electric vehicles is the use of technical and abstract parameters (such as the coefficient of technical level, technical excellence, etc.) or economic parameters (capital expenditures, specific cost, life cycle cost, etc.) as the universal criteria for comparison. Such parameters do not take into account specific operational conditions. Therefore, for an objective complex evaluation of the operational efficiency of the compared alternatives, it is necessary to carry out a statistical analysis of the operational modes, to create stochastic models of the functioning of the vehicles in real operational conditions and to simulate the compared variants in identical operating conditions.

Considering the complexity of the problem, its highly probabilistic nature and the presence of a number of uncertainties, the most objective decision can be found exclusively on the basis of a systematic approach. Cost-effective operations and the maintenance of a traction motor and the whole electric drive system require attention not only to individual units of the propulsion system, but to the system as a whole. A systems approach analyzes both the performance and demand sides of the system and how they interact, essentially shifting the focus from individual components to total system performance.

A common engineering approach is to break down a system into its basic components or units, to optimize the selection or design of those components, and then to assemble the system. One advantage of this approach is its simplicity. One disadvantage is that this approach ignores the interaction of the components. For example, a larger than necessary motor gives a safety factor and ensures that the motor can provide enough torque to meet the needs of the application. However, an oversized motor can also create performance problems with the driven equipment. In certain circumstances, an oversized motor can even compromise the reliability of both the components and the entire system.

In a component approach, an engineer employs a particular design that meets the unique requirements of a specific component. In a systematic approach, the entire system is evaluated in order to determine how end-use requirements can be provided mostly effectively and efficiently.

The study of different decision-making methods and of the comparative evaluation of complex technical systems, such as life cycle cost analysis (LCCA) [13], cost-benefit analysis (CBA) [1, 25], and multi-criteria analysis (MCA) [10, 29] for the purpose of choosing between alternatives, allow us to create a universal technique for the comprehensive assessment of traction electric motors [5, 9, 16, 17].

3.6.1 Brief Description of Methodology

3.6.1.1 Generalized Criteria

Chapter 1 provided a complete description of the method used in the comprehensive comparative assessment of the compliance of a vehicle’s propulsion systems with planned operating conditions. According to [10] and the requirements of the systematic approach, the target function of electric vehicles is the “sustainable, effective timely delivery of the required amount of cargo or passengers.” In accordance with the chosen target function, all the parameters are divided into two groups: those parameters which relate to the direct fulfillment of the target function of the vehicle—that is, to the criteria of “usefulness”—and those parameters which are related to the cost and damage involved in the fulfillment of the target function—that is, to the criterion of “payment for usefulness.”

Thus, “usefulness” is a non-financial analog of the benefits criterion of CBA and “payment for usefulness” is a near analog of the financial criterion of LCCA.

Based on the proposed technique and taking into account the requirements and conditions of future operations, the vehicle’s transportation productivity A was chosen as the criterion of “usefulness” for the vehicle’s entire lifetime:

$$A = DVt_{d} .$$
(3.6)
$$t_{d} = t_{o} k_{d} .$$
(3.7)

where D is the amount of transported cargo or passengers, V is the average operational speed; t o and t d are respectively operational and driving time in hours, and k d is the driving time rate.

As a second complex criterion C, “payment for usefulness,” was accepted as the sum of capital and operating cost and damage for the entire lifetime of the vehicle:

$$C = C_{CAP} + C_{CONST} + C_{F} + C_{RAC} + C_{EAC} .$$
(3.8)

where C CAP is capital cost, C CONST the fixed operating cost (personnel, navigation fees, taxis, insurance, etc.), C F the operating cost for fuel and oil, C RAC the reliability-associated cost [16] and C EAC the ecology-associated cost [5, 30].

The values of the parameters that are included in these two generalized criteria are dependent on the operational conditions of the vehicle in varying degrees. From the point of view of the operating conditions, the most informative parameters are the vehicle speed, the operating cost for fuel and oil, the reliability-associated cost and the ecology-associated cost.

3.6.1.2 Local Parameters

Considering the probabilistic nature of the vehicle movement process, it was advisable to introduce the value of the operational speed of the vehicle in the form of a multi-factor regression model (3.9).

$$V = f(x_{1} ,x_{2} , \ldots ,x_{n} ).$$
(3.9)

where \(x_{1} ,x_{2} , \ldots ,x_{n}\) are weakly correlated factors that affect the operational speed of the vehicle, such as the amount of transported cargo or passengers, the power of the main traction motor, the outside temperature, the strength and direction of the wind, etc.

It should be noted that the regression model takes into account factors explicitly included in the model, metric parameters of “usefulness,” and factors not included explicitly, such as the type of vehicle design, propulsive quality, maneuverability and other unmeasurable factors.

Thus, for the calculation of the generalized criterion of “usefulness,” it is necessary to determine the probability distribution (or average operational values) of these factors for the investigated operational area.

The calculation of values of C CAP and C CONST is a relatively simple problem and these values are not dependent on the vehicle’s operating conditions. The values of C F and C EAC are calculated based on the Markov model of energy generation E of diesel engines for the entire period of the vehicle’s operation:

$$C_{F} = c_{f} \sum\limits_{j} {e_{j} g_{j} } .$$
(3.10)

where c f is the specific fuel cost, e j the energy generation in the j-mode and g j the specific fuel consumption in the j-mode.

$$C_{EAC} = C_{F} \sum\limits_{i} {k_{i} d_{i} } .$$
(3.11)

where k i is the content of the harmful i-component in the burned fuel, C F the amount of the burned fuel and d i the specific damage from the combustion of the i-component of fuel.

For example, regarding trains and ships, for the further forecast of the value of C RAC , the Markov model of reliability of the repairable system [3, 5, 16, 17] is effective, as can be seen in Fig. 3.6.

Fig. 3.6
figure 6

The maintenance and repair system for trains and ships

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Using the Markov model, based on statistical operational data, we defined the availability coefficient of propulsion system K A for the vehicle’s lifetime. The value of the reliability-associated cost (RAC) was calculated using the formula:

$$C_{RAC} = c_{UR} t_{o} k_{d} \left( {1 - K_{A} } \right).$$
(3.12)

where c UR is the average specific cost of ship/train downtime due to the propulsion system’s unreliability and K A the coefficient of the propulsion system’s availability.

The average specific cost of outage takes into account the full range of expenses associated with the maintenance and repair of the propulsion system, whose shutdown grounds the vehicle. To simulate this process and to define C RAC for the entire period of operation of the vehicle, we used the method of statistical tests. A more detailed RAC assessment based on the Markov Reward models is presented in Chap. 4.

3.7 Ultimate Results for Icebreaker Ships

To carry out a comparative analysis, hybrid electric ships were selected as the application case. We chose them for investigation for the following reasons:

  • The preliminary analysis demonstrated the high competitiveness of the two types of traction motors—induction motor and synchronous motor with permanent magnets—for realizing the ship’s electric propulsion systems.

  • Restrictions on the weight and dimensions of the traction electric motor of the helicopter allow the use of traction PSM motors only.

  • The financial losses due to the wrong choice of traction electric motor for cars and trains are relatively small compared to the losses related to the development and design of the powerful electrical propulsion system installed in ships.

  • Due to the high capital cost, high operational cost and heavy expenses incurred in the event of damage, the choice of a traction motor that is not the optimal option for a ship’s electric propulsion system can lead to significant financial losses and to a decrease in the ship-owner’s profits.

  • A large amount of statistical data for the last five years of operation of the traction electric drive used in ships has been collected and systematized.

Thus, two types of ships designated for Arctic navigation—the Amguema-type Arctic ship (Fig. 3.7a) with a diesel-electric propulsion system (Fig. 3.8a) and the diesel-electric icebreaker “Ilya Muromets” (Fig. 3.8a, b)—were considered for evaluation.

Fig. 3.7
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The Amguema-type Arctic ship (a) and his propulsion system (b)

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Fig. 3.8
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The icebreaker “Ilya Muromets” (a) and his propulsion system (b)

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We have accepted the sustainable performance of transportation work with minimal cost as a main target function of these two types of ships, as noted in [5]. In this case, for the two types of ships that we compared and which perform the same target function, we must adopt the function “usefulness” with the same value for both compared ship types. In this case, in order to select the best option, we conducted out an analysis of the total cost and total damage over the 25 years of the ship’s lifetime [24, 30]. The remaining baseline data is presented in Table 3.8.

Table 3.8 Initial Data for Comparison
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Given the constantly changing cost of rare-earth metals, different variants of their prices were considered in the analyzing options. The difference in the cost of an IM and a PSM from 10%, up to 50% was taken into consideration as well. The results of the comparative assessment of the full life cycle of an Amguema-type Arctic ship and the icebreaker “Ilya Muromets” are shown in Tables 3.9 and 3.10 respectively. All the parameters in these tables are in millions of euros.

Table 3.9 Cost and damage for an Amguema-type Arctic ship
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Table 3.10 Cost and damage for the icebreaker “Ilya Muromets”
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The graphs plotted on the basis of the results of the calculations for the two types of ships are presented, respectively, in Figs. 3.9 and 3.10. The graphs contain the data on an Amguema-type Arctic ship with an IM, which costs 2 million euros (Fig. 3.9), and the data on the icebreaker “Ilya Muromets” with an IM, which costs 3 million euros (Fig. 3.10).

Fig. 3.9
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Amguema-type Arctic ship

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Fig. 3.10
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Icebreaker “Ilya Muromets”

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The simulation results show that, for both types of electric propulsion systems, a PSM is the preferred type of traction motor for such ships.

3.8 Conclusion

This chapter has presented the methodology of a two-step—preliminary and ultimate—selection of the appropriate electric traction motors for vehicular propulsion systems in different application cases. For some application cases, the results of the preliminary step indicate that there exists more than one adequate electrical machine type. For instance, for cars with specific requirements, it is possible to use any analyzed machine type, whereas, for aircraft applications, a permanent magnets synchronous motor appears to be the optimal choice, because an aircraft’s system requirements are rather challenging.

In cases where, in the wake of the preliminary analysis, it is not possible to decide what is the most suitable traction motor, the second step is proposed: the method of refined analysis based on stochastic models. To illustrate this point, we carried out an analysis and, based on that analysis, chose the optimum type of traction electric motor for ships with electric propulsion.

The results of the research showed that, when we take into account the full life cycle of a ship for all considered price variants of rare-earth magnets, a PSM has significant advantages in comparison with an IM. Moreover, the systematic efficiency of the PSM’s application as a traction electric motor increases with the increasing of the ship’s coefficient of technical use and running time rate. We have concluded that the cost of rare-earth magnets does not have a significant impact on the results of a comprehensive evaluation of electric motor variants and that a change in the cost of magnets by 50% leads to a change in the criterion of “payment for usefulness” by only 0.7%.