- Practice · 6 marks
Electric vehicle architecture and traction motors
Short answer
A BEV has a battery pack with BMS, inverter/motor controller, traction motor, single-speed reduction gear, on-board charger, and DC-DC for 12 V. Induction motor uses squirrel-cage rotor, lower cost; PMSM uses permanent magnets, higher efficiency (95-97%), higher power density but rare-earth magnet cost.
Draw the block diagram of a battery electric vehicle and explain its main components. Compare the induction motor and the permanent magnet synchronous motor (PMSM) used for traction.
Architecture of a battery electric vehicle (BEV)
Charger/AC inlet -> [Battery pack + BMS]
| (400 V DC)
DC-DC -> 12 V auxiliary battery
|
[Inverter] <- [Motor controller] <- Pedal
|
[Motor] -> single-speed gear -> wheels
- Battery pack: lithium-ion cells (300 to 800 V) that store the energy; the BMS manages it.
- On-board charger: converts AC mains to DC for charging; DC fast charging goes directly to the pack.
- Inverter / motor controller: converts DC to variable-frequency AC for the motor, controlled by the accelerator input. During regenerative braking it works in reverse, converting the motor's AC output to DC to charge the battery.
- Traction motor and transmission: the motor drives the wheels through a fixed reduction gear (6 to 10:1) and a differential; no clutch or multi-speed gearbox is required.
- DC-DC converter: steps the pack voltage down to 12 V for lights and electronics.
- Thermal management keeps the battery and motor at the right temperature, and regenerative braking recovers energy.
Induction motor vs PMSM
| Point | Induction motor | PMSM |
|---|---|---|
| Rotor | Squirrel cage, no magnets | Permanent magnets (NdFeB) |
| Efficiency | Good, 90 to 93 % | Higher, 95 to 97 % |
| Power density | Lower | Higher, compact |
| Cost | Lower, no rare earths | Higher, rare-earth magnets |
| Control | Vector control, with slip | Vector (field-oriented) control |
| Part-load efficiency | Lower | Better |
| Use | Tesla Model S (early), many buses | Nissan Leaf, most modern cars |
✓ Answer checked by Claude Opus 5.5 (high effort)
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