ABB DO820 Analog module industrial system controller

Description

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Does a DTC drive use fuzzy logic within its control loop?
No. Fuzzy logic is used in some drives to maintain the acceleration current within current limits and therefore prevent the drive
from tripping unnecessarily. As DTC is controlling the torque
directly, current can be kept within these limits in all operating
conditions.
A drive using DTC technology is said to be tripless. How has this been
achieved?
Many manufacturers have spent years trying to avoid trips during
acceleration and deceleration and have found it extraordinarily
difficult. DTC achieves tripless operation by controlling the actual
motor torque.
The speed and accuracy of a drive which relies on computed rather
than measured control parameters can never be realistic. Unless you are
looking at the shaft, you are not getting the full picture. Is this true with
DTC?
DTC knows the full picture. As explained above, thanks to the sophistication of the motor model and the ability to carry out 40,000
calculations every second, a DTC drive knows precisely what the
motor shaft is doing. There is never any doubt as to the motor’s
state. This is reflected in the exceptionally high torque response
and speed accuracy figures quoted on pages 18 and 19.
Unlike traditional AC drives, where up to 30 percent of all switchings are wasted, a drive using DTC technology knows precisely
where the shaft is and so does not waste any of its switchings.
DTC can cover 95 percent of all industrial applications. The
exceptions, mainly applications where extremely precise speed
control is needed, will be catered for by adding a feedback device to provide closed loop control. This device, however, can
be simpler than the sensors needed for conventional closed
loop drives.
Even with the fastest semiconductors some dead time is introduced.
Therefore, how accurate is the auto-tuning of a DTC drive?
Auto-tuning is used in the initial identification run of a DTC drive
(see page 29). The dead time is measured and is taken into account by the motor model when calculating the actual flux. If we
compare to a PWM drive, the problem with PWM is in the range
20 to 30 Hz which causes torque ripple.