Which is an advantage of PMAC motors?

• A. Higher efficiency due to no rotor losses
• B. Lower maintenance requirements
• C. Higher power density and better speed control accuracy
• D. Reduced manufacturing cost

Answer: (C)

Permanent magnet machines use magnets on the rotor and electronic control to drive the motor. This setup gives higher power density because you can produce the same or more torque with a smaller, lighter rotor since there are no rotor windings to carry current and their associated copper losses. The drive can regulate speed very precisely thanks to closed-loop control (often vector or field-oriented control), which decouples torque from flux and allows accurate speed response and tight regulation over a wide speed range. That combination—more torque from a smaller package and precise, fast speed control—is why this is the best advantage. The idea that there are no rotor losses is not accurate, since all machines have some losses (including magnet-related losses), and the other options don’t capture the primary practical benefit as effectively.