AC versus DC motors in EVs
Why almost every modern EV traction motor is fed with synthesised AC, even though the battery stores DC.
You'll learn
- Explain ac versus dc motors in evs at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real drive unit
Overview
EV batteries store DC, yet nearly every traction motor on the road today is an AC machine. The inverter's job is to bridge that gap.
In depth
Early EVs and some industrial drives used brushed DC motors, where mechanical brushes and a commutator switch current through the rotor windings as it spins. Brushes wear, arc, and limit speed and reliability — so virtually all modern traction motors are brushless AC machines, controlled electronically instead of mechanically.
Brushed DC vs modern AC traction motor
| Brushed DC | AC (PMSM/induction) | |
|---|---|---|
| Commutation | Mechanical brushes | Electronic inverter |
| Maintenance | Brush wear | Effectively none |
| Max speed | Limited by brush arcing | 15,000-20,000+ rpm |
| Efficiency | Lower (brush losses) | Higher |
| Control complexity | Simple | Requires sophisticated inverter |
Key takeaways
Remember this
- Batteries store DC; almost all EV traction motors run on AC.
- The inverter electronically replaces the mechanical commutator.
- Brushless AC motors are more efficient, faster-spinning and maintenance-free versus brushed DC.
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