ABB UK has announced a new generation of its direct torque control (DTC) to bring higher accuracy in motor speed and torque control, as well as the ability to control more types of motor.

This is the fourth generation of the DTC motor control platform used extensively in ABB’s variable-speed drives (VSDs) since 1996, and offers enhanced performance in open and closed loop and a higher switching frequency. Speed and torque control accuracy have been improved, for both dynamic and static values.

Support for high speed motors up to 500 Hz (as standard) and absolute encoder and resolver support are provided.  Other improvements include more choice of identification (ID) set-up runs, including standstill ID runs that allow the drive to identify the motor from its performance characteristics without the need to uncouple the motor from the load.

DTC lets users of the latest ABB industrial drives, ACS880, control any motor type without a change to the firmware, making it practical to use squirrel cage, permanent magnet and ABB’s advanced synchronous reluctance (SynRM) motors – the latest motor control technology offering high efficiency IE4 or high output compact motor variants.

The ACS880 drive offers fully functioning scalar control with its own ramps, fixed- and skip- speeds. Scalar is useful in multi-motor applications and can be used to test installations before switching to DTC; particularly useful when the test motor is not the same size as the motor to be used on site.

With DTC, field orientation is achieved without feedback, using advanced motor theory to calculate the motor torque. DTC uses fast digital signal processing hardware and an advanced mathematical understanding of how a motor works. The result is a drive with a torque response that is typically ten times faster than any AC or DC drive. This gives much improved process control and a more consistent product quality. The dynamic speed accuracy of DTC drives will be eight times better than any open loop AC drives and comparable to a DC drive that is using feedback.

Although DTC negates the need for speed feedback devices, accuracy can be further improved with an extensive range of encoders, resolvers and tachometers. 100% torque is available at zero speed on standard induction motors allowing the drives to be applied to high dynamic or highly arduous applications and can tackle any industrial application.

High dynamic torque control means applications such as grinders and crushers can be managed effectively, whilst the ability to generate torque at low speeds means DTC can effectively handle mixers or start fully loaded conveyors. DTC can be operated in master follower modes, making winders and strip lines easier to control, as well as cross travel or long travel crane control.

Winding applications

DTC offers torque control at low (or zero) speeds, particularly beneficial to cranes, hoists, winches or elevators, where the load needs to be started and stopped regularly without any jerking, and with load on the cables. The torque linearity offered by DTC allows an accurate and consistent level of winding, while its dynamic speed accuracy allows a motor to quickly recover to a stable state following a load change.

DTC allows the ACS880 drive to control fans or pumps that can be spinning at the start of the cycle, either forwards of backwards by smoothly catching the load and returning it to the desired speed.

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