Direct Torque Control (DTC) AC drive technology was developed by ABB and to replace traditional PWM drives in both open and closed-loop applications by providing precise torque control without the need for a feedback device. DTC is a feature of ABB high performance drives series ACS 800 and ACS880

DTC uses a control algorithm that is implemented on a microcontroller embedded in the drive. particularly in demanding applications. In addition to induction machines it can control synchronous machines such as wound rotor, permanent magnet and reluctance ones.

AC drives with frequency control using PWM (Pulse Width Modulation) controls the motor in the form of a pulse train dictating both the voltage and frequency. However, this control method is too inaccurate for many demanding applications.

AC drives with flux vector control were developed to emulate the magnetic operating conditions of a DC motor, however these require feedback device to achieve good torque response and speed accuracy: flux vector drives are therefore complex and expensive.

With DTC, field orientation is achieved without feedback, uses fast digital signal processing hardware and advanced motor theory to calculate the motor torque. The result is a drive with a torque response that is typically 10 times faster than any AC or DC drive. The dynamic speed accuracy of DTC drives will be 8 times better than any open loop AC drives and comparable to a DC drive that is using feedback.

User benefits

DTC provides precise torque control without the need for a feedback device to give fast torque response that reduces the speed drop time during a load transient to improve process control and a provide consistent motor output quality. Dynamic speed accuracy ensures a motor can quickly recover to a stable state after a sudden load change.

The improved torque control at low frequencies ensures smooth starting and stopping of loads that are stopped frequently such as cranes and lifts.  Torque linearity is important in precision applications like winders where an accurate and consistent level of winding is critical. Winder tension control can also be achieved from zero through to maximum speed.

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