**1. Introduction**

Electric vehicles (EVs) offer promising solutions for sustainable transport, but their develop‐ ment is hampered by a number of technological challenges [1–10]. To be competitive with internal combustion engines, EVs must offer the same dynamics, range, comfort conditions, and be cost effective [1, 2].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Since 2012, there has been an increase in the number of electric cars running on highways [3, 6, 8]. Most of them are powered by permanent magnet synchronous machines (PMSM)—due to their high energy from rare earths materials used for excitation—and sometimes by DC motors (DCM), for Renault ZOE model, induction machines (IM), or Tesla-S model. **Table 1** presents few of the best-selling electric cars, in series production, with some technical charac‐ teristics and their cost/unit. Apart from Tesla-S model, which is extremely expensive, car manufacturers are generally proposing motorization variants with approximately the same performance and features. The best sold model today is the Nissan Leaf, launched in December 2010; by December 2016, it should reach over 200,000 units sold globally. Among European variants, Renault-Zoe and BMW-i3 are the bestsellers, noting that the German car manufac‐ turer entered the market in the autumn of 2013 and by the end of this year, 2016, it should surpass 60,000 sold-ordered units. The number of electric units sold (globally surpassed the amount of 1 million units) is far from the number of internal combustion engine variants sold, one reason being the cost, in addition to the issue of autonomy. Basically, because of reduced autonomy and the reduced number of electric cars sold, the production cost/unit for EVs is high. Nevertheless, the trend is clear and with the increase in the number of supplying stations, the number of electric cars sold should increase exponentially.


**Table 1.** Some of the best-selling electric cars, in series production: propulsion's characteristics and approximate cost/ unit.

An interesting perspective was presented by the EVIG institute in 2013, see **Figure 1**. In their estimation, at the end of 2016 the number of cars sold should reach 2 million, and by the end of 2020 we should expect to have about 6 million electric cars running on streets. It looks promising, and we need to leave it to time to confirm their estimation.

The autonomy range of electric cars is affected by the load capacity and the energy storage capability, which is directly influenced by the total weight of the car and the propulsion's efficiency [2]. Thus, a closer look at the propulsion system should be considered.

The components of the drive chain are the electrical propulsion (electrical machine and transmission), the converter, and the battery—the energy flow within the system's components is bidirectional. The largest share of losses is in the electrical propulsion, 72%, on the static converter the loss is about 19%, and at the battery level the loss is about 9% (**Figure 2**).

**Figure 1.** Perspective on the sold electric cars, worldwide.

Since 2012, there has been an increase in the number of electric cars running on highways [3, 6, 8]. Most of them are powered by permanent magnet synchronous machines (PMSM)—due to their high energy from rare earths materials used for excitation—and sometimes by DC motors (DCM), for Renault ZOE model, induction machines (IM), or Tesla-S model. **Table 1** presents few of the best-selling electric cars, in series production, with some technical charac‐ teristics and their cost/unit. Apart from Tesla-S model, which is extremely expensive, car manufacturers are generally proposing motorization variants with approximately the same performance and features. The best sold model today is the Nissan Leaf, launched in December 2010; by December 2016, it should reach over 200,000 units sold globally. Among European variants, Renault-Zoe and BMW-i3 are the bestsellers, noting that the German car manufac‐ turer entered the market in the autumn of 2013 and by the end of this year, 2016, it should surpass 60,000 sold-ordered units. The number of electric units sold (globally surpassed the amount of 1 million units) is far from the number of internal combustion engine variants sold, one reason being the cost, in addition to the issue of autonomy. Basically, because of reduced autonomy and the reduced number of electric cars sold, the production cost/unit for EVs is high. Nevertheless, the trend is clear and with the increase in the number of supplying stations,

the number of electric cars sold should increase exponentially.

742 Modeling and Simulation for Electric Vehicle Applications

**Citroen C-ZEROs** PMSM 47 kW 130 km/h 100 km Li-I battery; **30€**;

promising, and we need to leave it to time to confirm their estimation.

unit.

**Model EM EM power Top speed Autonomy Other characteristics and price Renault ZOE** DCM 43/65 kW 135 km/h 100 km 22 kWh/400 V Li-I battery; **27k€**;

**Peugeot iOn** PMSM 47 kW 130 km/h 100 km Li-I battery; 0–100km/h:16s; **30k€ Nissan Leaf** PMSM 80 kW 150 km/h 121 km 24 kWch Li-Manganate battery; **29k\$**; **BMW-i3** PMSM 65 kW 150 km/h 130 km 360 V Li-I battery; 0–60 km/h:< 4 s; **41k\$**; **Smart electric** PMSM 35 kW 125 km/h 145 km Li-I battery; 0–60 km/h: 4.8 s; **20k\$ Mitsubishi i-MiEV** PMSM 49 kW 130 km/h 100 km 16 kW/330 V Li-I battery; **34k\$ Tesla S** IM 225 kW 193 km/h 335 km 60 kWh battery; 0–100km/h:<6s; **71k\$**

**Table 1.** Some of the best-selling electric cars, in series production: propulsion's characteristics and approximate cost/

An interesting perspective was presented by the EVIG institute in 2013, see **Figure 1**. In their estimation, at the end of 2016 the number of cars sold should reach 2 million, and by the end of 2020 we should expect to have about 6 million electric cars running on streets. It looks

The autonomy range of electric cars is affected by the load capacity and the energy storage capability, which is directly influenced by the total weight of the car and the propulsion's

The components of the drive chain are the electrical propulsion (electrical machine and transmission), the converter, and the battery—the energy flow within the system's components

efficiency [2]. Thus, a closer look at the propulsion system should be considered.

**Figure 2.** Losses in the propulsion system.

Therefore, acting mainly on the electrical propulsion by improving its efficiency and power density will improve the overall autonomy of the EV [3–5].

With regard to the existing propulsion solution, it can be seen that over time, the operating speed has substantially increased [11–19]. As an example, let us take a look at few seriesmanufactured cars: if in 2003, the electric motor of the Toyota-Prius-Hybrid was at 6000 r/min, the latest model is running at 12,000 r/min [9]; for the BMW-i3 model, the nominal speed is 4000 r/min, while the maximum speed (in flux-weakening operating conditions) is 11,800 r/ min; for the present Mitsubishi-iMiev model, the speed of the motor is 9000 r/min. We can conclude that all car manufacturers are looking at increasing the speed of motorization, having in mind the improvisation of power density of the traction chain, as well as EV's autonomy.

In this context, we should recall that higher speeds are not easily and efficiently possible, since attached to the electric motor a gear is placed in order to transfer the torque-speed to the car's traction wheels. For a tire diameter of about 0.6 m and a circumferential speed of 1500 r/min coming from the gear, the vehicle's traveling speed is 47 m/s, meaning 169 km/h. In such a case, even if we would like to increase the speed of the propulsion motor, a classic mechanical gear with high transmission ratio is difficult to obtain; usually, we consider cascaded gear units, but this will affect the global power density of the traction system and its efficiency. Thus, a solution is needed to overcome this drawback. In this context, the use of a magnetic gear (MG) could be the right solution.

In **Table 2**, a weight comparison of the possible motorization solutions is presented, based on personal experience or technical data found on the available equipment.


**Table 2.** Comparison of traction chain weights for different configurations containing classic or magnetic gears.

For the sake of comparison, we have considered three possible variants: one motorization with 6500 r/min, another one with high-speed motor (running at 26,000 r/min), while the traction is used with a fixed mechanical gear ratio, or with multilevel gear (to reach the desired ratio), or when, for the same high-speed machine, we have a magnetic gear (MG) excited with rare earth material. **Table 2** shows how for the same converter and battery pack, high-speed motorization has a reduced weight with about 80 kg (with fixed mechanical gear). Otherwise, when using an MG with high transmission ratio, the performance and power density are high, while the weight of the entire propulsion system is decreased by about 130 kg—which is a huge win for an EV.

The detailed structure of a magnetic gear will be presented in the next section. Here, we should recall that the main materials found on a magnetic gear are the permanent magnet for excitation, and the steel. Thus, the MG has one important disadvantage: it is extremely expensive because the excitation (on both rotating parts—the low-speed rotors—which are interacting for the production of the torque) is generally made of Nd-Fe-B. According to **Table 3**, at the present time, the most important rare earth resources are found in Asia, particularly in China; even the European production is under Hitachi license—meaning that it is again an Asian license. Due to the monopoly imposed by Asian countries, the price of this type of material reached 130 €/kg in 2010–2011 (from 50 €/kg in 2002), now being stabilized after a slight decrease at 100–110 €/kg. As a consequence, the European and other countries are trying to avoid this monopoly. Moreover, the global earth resources in terms of rare earth materials cannot cover today's industry needs.


**Table 3.** Worldwide production of Nd-Fe-B at the 2013-year level.

case, even if we would like to increase the speed of the propulsion motor, a classic mechanical gear with high transmission ratio is difficult to obtain; usually, we consider cascaded gear units, but this will affect the global power density of the traction system and its efficiency. Thus, a solution is needed to overcome this drawback. In this context, the use of a magnetic

In **Table 2**, a weight comparison of the possible motorization solutions is presented, based on

**steps**

≈8 kg

steps

**Table 2.** Comparison of traction chain weights for different configurations containing classic or magnetic gears.

For the sake of comparison, we have considered three possible variants: one motorization with 6500 r/min, another one with high-speed motor (running at 26,000 r/min), while the traction is used with a fixed mechanical gear ratio, or with multilevel gear (to reach the desired ratio), or when, for the same high-speed machine, we have a magnetic gear (MG) excited with rare earth material. **Table 2** shows how for the same converter and battery pack, high-speed motorization has a reduced weight with about 80 kg (with fixed mechanical gear). Otherwise, when using an MG with high transmission ratio, the performance and power density are high, while the weight of the entire propulsion system is decreased by about 130 kg—which is a

The detailed structure of a magnetic gear will be presented in the next section. Here, we should recall that the main materials found on a magnetic gear are the permanent magnet for excitation, and the steel. Thus, the MG has one important disadvantage: it is extremely expensive because the excitation (on both rotating parts—the low-speed rotors—which are interacting for the production of the torque) is generally made of Nd-Fe-B. According to **Table 3**, at the present time, the most important rare earth resources are found in Asia, particularly in China; even the European production is under Hitachi license—meaning that it is again an Asian license. Due to the monopoly imposed by Asian countries, the price of this type of

**High speed (26000 r/min, water cooled) with mechanical gear in**

Decreased volume and weight, efficiency affected by the gear in **High speed (26000 r/min, water cooled), magnetic gear**

Reduced volume and weight, increased efficiency, limitation for wide-speed operation

**with 1 fix step**

personal experience or technical data found on the available equipment.

**Motorization** (30 kW) 130 kg 16 kg 16 kg **Gear** ≈50 kg ≈80 kg 33 kg

**Total weight ≈388 kg** ≈**304 kg** ≈**257 kg**

**Classic (low speed) with mechanical gear**

**Battery** (380 Vcc, 18 kWh) ≈200 kg

weight, acceptable efficiency

**Remarks** Increased volume and

gear (MG) could be the right solution.

764 Modeling and Simulation for Electric Vehicle Applications

**Component Electric propulsion**

**Converter** (30 kW/water

huge win for an EV.

cooled)

As a result, an important decision was first taken in 2012, when the European Research Agency (ERA) said that it will not fund research projects that use rare earth materials, such as Nd-Fe-B or Sm-Co type; it is for this reason that research institutes and universities have lately reconsidered the use of ferrite material (5 €/kg) or the possibility to avoid any excitation material, by means of passive rotors, such as reluctance synchronous machines (RSM). Some others are trying to reduce the volume of rare earth materials, calling such machines as PMassisted ones.

Otherwise, from previous research experience and information found in the literature, it has been observed that a magnetic gear with specific configuration of poles/teeth will induce specific torque ripples in the propulsion system [25–31]. Thus, when thinking of an MG, we are interested in finding an appropriate configuration which produces the lowest vibration and noise level. These elements will be considered with respect to the MG topic, while considering it for the EV application.
