Innovative and Highly Integrated Modular Electric Drivetrain
2.1. Permanent Magnet Hybrid Synchronous Machine
2.1.1. Machine Design
- Since the current capability of the gallium nitride inverter is expected to be low, the missing torque through current must be compensated by highest power magnets.
- Due to the high speeds of the rotor, the small rotor cross section does not provide sufficient space to design a mechanically stable rotor with a high mass of ferrite magnets (which would be needed in order to produce the same air gap flux as with NdFeB magnets).
- Ferrite magnets of currently available grades are not sufficiently safe against demagnetization.
2.1.2. Magnet Injection Moulding
2.2. GaN Inverter
2.2.1. Advantages of Gallium Nitride Devices
- an unrivalled switching performance with switching on/off in less than 10 ns,
- a low package inductance,
- a low on-resistance
- and reduced switching losses: five times better than Si devices and two times better than SiC devices.
2.2.2. GaN Power Board Conception
2.2.3. Series-independent Winding Reconfiguration
2.2.4. Simulation Results of Winding Reconfiguration
2.2.5. Experimental Results of Winding Reconfiguration.
2.2.6. Industrialization Potential of GaN Devices
- Overall powertrain efficiency during type approval cycles: no clear winner between the two options
- A dual ratio transmission with adapted ratios provides higher launch torque in first gear and higher top speed for the same motor speed in the second gear: this benefits the projects demonstrator that has limited motor torque due to the current limitations of the available GaN devices.
- Market demand: some customers prefer a dual ratio transmission for EV powertrains for particular reasons (e.g., gradeability, large difference between empty vehicle mass and fully loaded vehicle mass).
2.4. Module Assembly and Final Specifications
2.5. Holistic Design Approach
- Electric Machine: High-speed EM generates power over high speeds and therefore, does need less winding current than low-speed EM. Ohmic losses in the windings are reduced while the iron losses slightly rise. However, the savings in winding losses surpass the additional iron losses and the machine is more efficient.
- Inverter: Classical Si-based inverters are still a good choice for slow to medium switching frequencies. At high switching frequencies, GaN and SiC provide a suitable characteristic. The latter option leads to very compact inverters, as the size of the DC-link capacitor can be reduced with higher switching frequencies.
- Transmission: With higher maximum EM speeds, higher reduction ratios are required and the transmission gets bigger and less efficient. For high reduction ratios, more complex topologies show advantages compared to simple spur gear designs.
- Module Level: A module based on a high speed electric machine as presented above is more efficient and compact compared to conventional modules, even though the transmission itself is not. The drawbacks on the transmission side are overcompensated by the advantages on the machine and inverter side. However, due to high switching frequencies, conventional IGBTs produce high switching losses and thus, wide bandgap materials (GaN and SiC) should be used. Based on the current cost structures, the use of these materials results in a higher price on module level.
Conflicts of Interest
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|Parameter||ModulED Motor with Sintered Magnets||ModulED Motor with Injected Magnets||Reference Motor: BMW i3|
|Peak phase current (A rms)||225||225||410|
|Winding type||Formed Litz||Formed Litz||Classical Litz|
|Number of phases||6||6||3|
|Nominal speed (rpm)||8600||8600||5000|
|Max speed (rpm)||22,500||22,500||11,400|
|Peak torque (Nm)||160||156||250|
|Peak power (kW)||157||158||131|
|Battery voltage (VDC)||320||320||360|
|Stator outer diameter (mm)||176||176||242|
|Stator inner diameter (mm)||118||118||180|
|Stack length (mm)||179||179||130|
|Magnet Weight (kg)||1.32||1.73||2.02|
|Peak power @360 VDC (kW)||177||178||131|
|Magnet weight per kW (g)||7.5||9.7||15.4|
|Magnet reduction compared to reference motor (%)||52||40||0|
|Width, length & height (W × L × H as in Figure 19)||405 × 513 × 275 mm|
|Peak power at wheels||157 kW|
|Peak torque at wheels||3460 Nm|
|Required battery DC voltage||320 V|
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Hemsen, J.; Kieninger, D.; Eckstein, L.; Lidberg, M.R.; Huisman, H.; Arrozy, J.; Lomonova, E.A.; Oeschger, D.; Lanneluc, C.; Tosoni, O.; et al. Innovative and Highly Integrated Modular Electric Drivetrain. World Electr. Veh. J. 2019, 10, 89. https://doi.org/10.3390/wevj10040089
Hemsen J, Kieninger D, Eckstein L, Lidberg MR, Huisman H, Arrozy J, Lomonova EA, Oeschger D, Lanneluc C, Tosoni O, et al. Innovative and Highly Integrated Modular Electric Drivetrain. World Electric Vehicle Journal. 2019; 10(4):89. https://doi.org/10.3390/wevj10040089Chicago/Turabian Style
Hemsen, Jonas, Daniel Kieninger, Lutz Eckstein, Mathias R. Lidberg, Henk Huisman, Juris Arrozy, Elena A. Lomonova, Daniel Oeschger, Charley Lanneluc, Olivier Tosoni, and et al. 2019. "Innovative and Highly Integrated Modular Electric Drivetrain" World Electric Vehicle Journal 10, no. 4: 89. https://doi.org/10.3390/wevj10040089