Comparison and selection of electric vehicle propulsion system

22. Február, 2012, Autor článku: Noge Filip, Elektrotechnika, Študentské práce
Ročník 5, číslo 2 This page as PDF Pridať príspevok

The work compares and evaluates various kinds of electric propulsion for vehicles. At the beginning we set the conditions for comparison. We are interested in output parameters such as acceleration, top speed and gear ratios. Finally, the best system is chosen with an explanation of why this is the best.

1. Introduction – Electro mobility

Low efficiency, limited supply of energy sources, mechanical limits are the main problems related to transportation and automotive industry. Mankind should solve this problem with combustion engine. There are already several concepts to replace the combustion engines and most of them directed to electric vehicles, whether by a plug-in full electric vehicle or a vehicle with a fuel cell. Presently, we still did not replace combustion engines by electro mobility because we have enough fuel and we can not properly store electricity in batteries, but it becomes more and more recent. Therefore, I have decided to choose and propose full electric vehicle.

2. Traction propulsion

The goal was to create the vehicle propulsion, which we comply with the following parameters in order of priority: acceleration, maximum speed, as low weight. The task is to select a suitable motor and project propulsion system. The system has been solved under following circumstances which are shown in the table 2.1.

Tab. 2.1. Circumstances for calculations

Circumstances for calculations
gravitational acceleration g 9,81 m.s-2
air density ρo 1,22 kg.m-3
air resistance coefficient cx 0,3
rolling resistance coefficient fv 0,01
coefficient of rotational mass inertia δ 0,5
frontal area of vehicle S 1,2 m2
vehicle weight m 1200 kg
wheel dynamic radius rd 0,3 m

Tab. 2.2. Main equations and units.

Basic equation Units Used equation Units
P=M2 \pi n [P]=W
[M]=Nm
[n]=s-1		 P=\frac{M2 \pi n}{6000} [P]=kW
[M]=Nm
[n]=ot/min
F=\frac{Mi_c}{r_d} [F]=N
[M]=Nm
[rd]=m		 F=\frac{Mi_c}{r_d} [F]=N
[M]=Nm
[rd]=m
v=\frac{2 \pi r_d n}{i_c} [v]=ms-1
[rd]=m
[n]=s-1		 v=3.6 \frac{2 \pi r_d n}{60i_c} [v]=km/h
[rd]=m
[n]=ot/min

The next chapter contains three best electro-motors in matter of performance in comparison to many other available motors.

3. EVO 240


Fig. 3.1 Image of the EVO 240 electric motor

3.1 Parameters of the EVO 240

Tab. 3.1. EVO 240 specifications

MOTOR
Dimensions L 222 D 400 mm
Maximal peak torque 800 Nm
Maximal peak power 335 kW
Maximal nominal torque 440 Nm
Maximal nominal power 150 kW
Maximal RPMs 5000 ot/min
Weight 80 kg
Maximal efficiency 96,5%
INVERTOR
Dimensions 643x340x166 mm
Voltage range 300-720 V
Maximal current 343 A
Weight 30 kg


3.2 Characteristics of the EVO 240

Tab. 3.2. EVO 240 performance curves table

torque and power vs. RPMs
Pnom Mnom Pmax Mmax n
0,00 440,00 0,00 800,00 0
22,51 430,00 41,89 800,00 500
43,98 420,00 83,78 800,00 1000
54,32 415,00 104,72 800,00 1250
64,40 410,00 125,66 800,00 1500
83,78 400,00 167,55 800,00 2000
102,10 390,00 209,44 800,00 2500
119,38 380,00 251,33 800,00 3000
135,61 370,00 293,22 800,00 3500
150,80 360,00 335,10 800,00 4000
150,80 320,00 341,65 725,00 4500
146,61 280,00 340,34 650,00 5000

where: Mmax is peak torque [Nm], Pmax is peak power [kW], Mnom is nominal torque [Nm], Pnom is nominal power [kW], n is RPMs [1/min]

Tab. 3.3. Table of total gear ratios for EVO 240

Total gear ratios ic1 4
ic2 3,375
ic3 2,75
ic4 2,125
ic5 1,5

Where icx is the total gear ratio of gear with corresponding index. The vehicle is approximately able (with this motor and gearing) to achieve an average acceleration 9,78 ms-2, which means acceleration from 0 to 100 km/h in 2,84 s on the first gear.


Fig. 3.2. EVO 240 performance curves


Fig. 3.3. EVO 240 propulsion force vs. RPMs chart

3.3 Appreciation, advantages and disadvantages of the EVO 240

This motor with its properties are on the leading positions in comparison with other motors, and although it too expensive it has very good torque to price ratio as well as power to price ratio and I assume that in terms of parameters is the most appropriate candidate from analyzed motors.The advantages of this motor are its small size, light weight, excellent parameters and performance curves, and also that it is supplied with an inverter designed exactly for this motor.

Disadvantages are high cost and complicated availability. An interesting fact is the starting torque during short time current overload, which the other motors datasheets do not contain. Its value is 1200 Nm for 18 seconds, so we could use this as a benefit in our application. (peak torque is the motor able to withstand for 60 seconds).

3.4 The cooling requirements of the EVO 240

The motor requires liquid cooling and its structure includes cooling system. Only the pipe connections with coolant and adequate volumetric flow need to be provided for the system startup. The maximum value of volumetric flow rate could not exceed 12 l / min. Mixture of water with ethylene glycol (antifreeze standard component of coolant in the automotive industry) in a 1:1 ratio is recommended as the cooling medium.

4. UQM 200


Fig. 4.1 Image of the UQM 200 electric motor

4.1 Parameters of the UQM 200

Tab. 4.1. UQM 200 specifications

MOTOR
Dimensions L 241 D 411 mm
Maximal peak torque 900 Nm
Maximal peak power 200 kW
Maximal nominal torque 450 Nm
Maximal nominal power 115 kW
Maximal RPMs 5500 ot/min
Weight 95 kg
Maximal efficiency 94%
INVERTOR
Dimensions 380x365x119 mm
Voltage range 240 – 440 V
Maximal current 600 A
Weight 15,9 kg


4.2 Characteristics of the UQM 200

Tab. 4.2. UQM 200 performance curves table

torque and power vs. RPMs
Pnom Mnom Pmax Mmax n
0 455 0 900 0
24 455 48 900 500
48 455 96 900 1000
54 440 120 900 1250
66 425 132 860 1500
82 400 160 760 2000
98 375 176 680 2500
115 360 190 600 3000
115 320 200 550 3500
115 270 200 480 4000
108 240 200 440 4500
96 185 200 380 5000

where: Mmax is peak torque [Nm], Pmax is peak power [kW], Mnom is nominal torque [Nm], Pnom is nominal power [kW], n is RPMs [1/min]

Tab. 4.3. Table of total gear ratios for UQM 200

Total gear ratios ic1 4
ic2 3,75
ic3 3
ic4 2,25
ic5 1,5

Where icx is the total gear ratio of gear with corresponding index. The vehicle is approximately able (with this motor and gearing) to achieve an average acceleration 9,84 ms-2, which means acceleration from 0 to 100 km/h in 2,82 s on the first gear.


Fig. 4.2. UQM 200 performance curves


Fig. 4.3. UQM 200 propulsion force vs. RPMs chart

4.3 Appreciation, advantages and disadvantages of the UQM 200

This motor has the highest value of torque in comparison to others considered, this means it has the highest value of torque, and although it is quite expensive it has a very good torque to price ratio as well as power to price ratio and I assume that in terms of parameters is the most appropriate candidate from analyzed motors.

The advantages of this motor are its small size, light weight, excellent parameters and performance curves, and also that it is supplied with an inverter designed exactly for this motor. Disadvantages are high cost and complicated availability. Possibility of short time current overload and also the time period that the system could withstand are unknown.

4.4 The cooling requirements of UQM 200

The motor requires liquid cooling and its construction includes cooling system. Only the pipe connections with coolant and adequate volumetric flow need to be provided for the system startup. The maximum value of volumetric flow rate should not exceed 7,5 l / min and maximum value of pressure in cooling system should not exceed 0,7 bar. Mixture of water with ethylene glycol (antifreeze standard component of coolant in the automotive industry) in a 1:1 ratio is recommended as the cooling medium.

5. Symetron P-200


Fig. 5.1 Image of the Symetron P-200 electric motor

5.1 Parameters of Symetron P-200

Tab. 5.1. Symetron P-200 specifications

MOTOR
Dimensions L 457 D 279 mm
Maximal peak torque 415 Nm
Maximal peak power 200 kW
Maximal nominal torque 207 Nm
Maximal nominal power 100 kW
Maximal RPMs 5500 ot/min
Weight 112 kg
Maximal efficiency 93%
INVERTOR
Dimensions 224x330x358 mm
Voltage range 500 – 700 V
Maximal current ? A
Weight 36 kg


5.2 Characteristics of the Symetron P-200

Tab. 5.2. Symetron P-200 performance curves table

torque and power vs. RPMs
Pnom Mnom Pmax Mmax n
0,00 207,00 0,00 415,00 0
10,84 207,00 21,73 415,00 500
21,68 207,00 43,46 415,00 1000
32,52 207,00 65,19 415,00 1500
43,35 207,00 86,92 415,00 2000
54,19 207,00 108,65 415,00 2500
65,03 207,00 130,38 415,00 3000
75,87 207,00 152,11 415,00 3500
86,71 207,00 173,83 415,00 4000
97,55 207,00 195,56 415,00 4500
97,91 187,00 198,97 380,00 5000
97,91 170,00 201,59 350,00 5500
97,39 155,00 201,06 320,00 6000
95,29 140,00 199,44 293,00 6500
93,10 127,00 197,92 270,00 7000
93,46 119,00 196,35 250,00 7500
92,15 110,00 196,87 235,00 8000
93,46 105,00 195,83 220,00 8500
94,25 100,00 197,92 210,00 9000
95,50 96,00 201,95 203,00 9500
99,48 95,00 204,20 195,00 10000

where: Mmax is peak torque [Nm], Pmax is peak power [kW], Mnom is nominal torque [Nm], Pnom is nominal power [kW], n is RPMs [1/min]

Tab. 5.3. Table of total gear ratios for Symetron P-200

Total gear ratios ic1 9
ic2 7,375
ic3 5,75
ic4 4,125
ic5 2,5

Where icx is the total gear ratio of gear with corresponding index. The vehicle is approximately able (with this motor and gearing) to achieve an average acceleration 9,44 ms-2, which means acceleration from 0 to 100 km/h in 2,94 s on the first gear.


Fig. 5.2. Symetron P-200 performance curves


Fig. 5.3. Symetron P-200 propulsion force vs. RPMs chart

5.3 Appreciation, advantages and disadvantages of the Symetron P-200

The motor including its parameters is above average but not apparently excellent, which is not a problem if they are sufficient, so this should be well considered. Its advantage is the relatively high power and broadband RPMs. The main disadvantages are high weight, a high supply voltage and relatively large dimensions. Torque value is lower, but still sufficient.

5.4 The cooling requirements of the Symetron P-200

Cooling is provided by fluid coolant that is used in most of motors. Details of cooling are not known. Mixture of water with ethylene glycol (antifreeze standard component of coolant in the automotive industry) in a 1:1 ratio is recommended as the cooling medium.

6. Conclusion

First of all let’s look at gearbox. We can say, that it is necessary to implement gearbox, because it provides the opportunity to achieve excellent acceleration and high value of maximal speed, so that is the reason why we do not want to use permanent ratio or without any ratio conception. There is one solution that could be comparable to conception with gearbox. It is conception with two motors without gearbox (or with permanent ratio). This conception has major problem with power consumption. It means that two motors consume twice value of energy. This solution requires more batteries and cause more weight. That is the reason why we incorporate the gearbox.

Now let’s look at the motor choice. From all the candidates we choose the EVO 240 as the best alternative. It has great performance curves and it is relatively lightweight. There might be a question, if the gearbox is strong enough to transfer high torque that the motor provides. We should not forget that the calculations were provided not considering the losses (efficiency). This means that the real result value will be lower, but to compare the systems the calculations are appropriate.

References

  1. http://www.evo-electric.com/products/
  2. http://www.uqm.com/propulsion_specs.php
  3. http://www.raserev.com/category/motors-and-drives/motors
Coauthor of this paper is Ing. Vladimír Staňák, Katedra mechaniky, Fakulta elektrotechniky a informatiky, Slovenská technická univerzita, 812 19 Bratislava, Slovenská republika

Práca bola prezentovaná na Študentskej vedeckej a odbornej činnosti (ŠVOČ 2011) v sekcii Aplikovaná mechanika II a získala Cenu dekana, ISBN 978-80-227-3508-7

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