Direct Torque Control – A Galco Blog Tech Tip

Direct torque control or DTC is one method used in variable frequency drives to control the torque (and thus the speed) of three-phase AC electric motors.

DTC controls motor flux and torque directly, instead of trying to control motor currents indirectly like AC vector drives and DC drives. This means better accuracy in matching the driven system’s load requirements.

 

 

Direct torque control works by first estimating flux magnitude and torque, then comparing those estimates to reference values. Stator flux linkage is estimated by integrating the stator voltages. Torque is estimated as a cross product of estimated stator flux linkage vector and measured motor current vector.

If either the estimated flux or torque deviates too far from the reference tolerance, the transistors of the variable frequency drive are turned off and on in such a way that the flux and torque errors will return in their tolerant bands as fast as possible

Besides superior torque response, DTC offers other customer benefits, including:

  • No need for motor speed or position feedback in 95% of applications, eliminating the need for costly encoders or other feedback devices
  • DTC control available for different types of motors, including permanent magnet
  • Accurate torque and speed control down to low speeds, as well as full startup torque down to zero speed
  • High static and dynamic speed accuracy
  • No preset switching frequency. Optimal transistor switching is determined for every control cycle, allowing the drive to more readily match driven load requirements.

 

For more information about direct torque control and variable frequency drives, contact our experts today!

 

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