In this section we will distinguish between permanent magnet synchronous machines (PMSMs) and brushless DC (BLDC) motors. Both rely on permanent magnets on the rotor but differ in their construction and control.
Key differences
- Winding configuration: BLDC machines typically use trapezoidal back-EMF profiles and are driven with square-wave currents, whereas PMSMs have sinusoidal back-EMF and use sinusoidal currents for smooth torque.
- Control strategy: BLDC motors use six-step commutation; PMSMs employ field‑oriented control (FOC) for precise torque production.
- Applications: BLDC motors are common in simple drives and cost-sensitive applications. PMSMs dominate in high-performance applications such as electric vehicles.
Rotary vs linear machines
While this site focuses on rotary machines, the same principles extend to linear permanent magnet machines with appropriate coordinate transforms.
Takeaways
- The main difference lies in the shape of the back-EMF and current waveforms.
- PMSMs offer smoother torque and are easier to model analytically.
- BLDC control is simpler but yields higher torque ripple.