DTC Questions & Answers (1)

General

What is Direct Torque Control?
Direct Torque Control – or DTC as it is called – is set to replace traditional PWM drives of the open- and closed-loop type in the near future.

Why is it called Direct Torque Control?
Direct Torque Control describes the way in which the control of torque and speed are directly based on the electromagnetic state of the motor, similar to a DC motor, but contrary to the way in which traditional PWM drives use input frequency and voltage. DTC is the first technology to control the “real” motor control variables of torque and flux.
What is the advantage of this?
Because torque and flux are motor parameters that are being directly controlled, there is no need for a modulator, as used in PWM drives, to control the frequency and voltage. This, in effect, cuts out the middle man and dramatically speeds up the response of the drive to changes in required torque. DTC also provides precise torque control without the need for a feedback device.
Why is there a need for another AC drive technology?
DTC is not just another AC drive technology. Industry is demanding more and existing drive technology cannot meet these demands.
For example, industry wants:
• Better product quality which can be partly achieved with improved speed accuracy and faster torque control.
• Less down time which means a drive that will not trip unnecessarily; a drive that is not complicated by expensive feedback devices; and a drive which is not greatly affected by interferences like harmonics and RFI.
• Fewer products. One drive capable of meeting all application needs whether AC, DC or servo. That is a truly “universal” drive.
• A comfortable working environment with a drive that produces much lower audible noise.
Who invented DTC?
ABB has been carrying out research into DTC since 1988 foll owing the publication of the theory in 1971 and 1985 by German doctor Blaschke and his colleague Depenbrock. DTC leans on the theory of field oriented control of induction machines and the theory of direct self control. ABB has spent over 100 man years developing the technology.

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