BLDC motors and hub motor applications
Trapezoidal control, and where brushless DC motors still make sense in EVs.
- Explain bldc motors and hub motor applications at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real drive unit
Overview
Brushless DC (BLDC) motors are close cousins of PMSMs, distinguished mainly by simpler trapezoidal — rather than sinusoidal — control, and remain common in smaller EVs, e-bikes and auxiliary drives.
In depth
A BLDC motor is electromagnetically similar to a surface-mounted PMSM, but is traditionally driven with simple trapezoidal (six-step) commutation using basic Hall-effect sensors, rather than the continuous sinusoidal field-oriented control used in most traction PMSMs. This makes controllers cheaper and simpler, at the cost of more torque ripple.
Where hub motors fit
Hub motors integrate the motor directly into the wheel, eliminating the driveshaft and gearbox entirely. This is common on e-bikes, e-scooters and some low-speed EVs, but rarely used for full-size passenger car traction because it adds unsprung mass, harming ride and handling.
Key takeaways
- BLDC motors are similar to PMSMs but typically use simpler trapezoidal commutation.
- Trapezoidal control is cheaper but produces more torque ripple than sinusoidal FOC.
- Hub motors eliminate the drivetrain but add unsprung mass, limiting their use in passenger cars.
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