Which statement is true about torque in a VFD-controlled motor across the speed range?

Which statement is true about torque in a VFD-controlled motor across the speed range?

• A. The motor maintains full torque throughout the speed range.
• B. Torque drops to zero at low speed.
• C. Torque is independent of the drive.
• D. Torque is not a consideration.

Answer: (A)

Torque in a VFD-driven motor is controlled primarily by current. The drive adjusts voltage and frequency to push the motor current to the level needed for the desired torque, so the motor can deliver its rated torque across speeds up to the point where the drive’s voltage limit would restrict further torque. This means you can start the motor and run it at speed while maintaining the full rated torque, rather than losing torque as speed changes. Beyond the base speed, the drive may have to trim torque to stay within power limits, but across the range where the drive can supply the needed current, the torque remains essentially full. That’s why the option claiming full torque across the speed range is the best fit. The other statements misstate how the drive and motor behave: torque isn’t independent of the drive, it isn’t naturally zero at low speed, and torque is a real consideration in how the system is controlled.

Torque in a VFD-driven motor is controlled primarily by current. The drive adjusts voltage and frequency to push the motor current to the level needed for the desired torque, so the motor can deliver its rated torque across speeds up to the point where the drive’s voltage limit would restrict further torque. This means you can start the motor and run it at speed while maintaining the full rated torque, rather than losing torque as speed changes. Beyond the base speed, the drive may have to trim torque to stay within power limits, but across the range where the drive can supply the needed current, the torque remains essentially full. That’s why the option claiming full torque across the speed range is the best fit. The other statements misstate how the drive and motor behave: torque isn’t independent of the drive, it isn’t naturally zero at low speed, and torque is a real consideration in how the system is controlled.