ABB DO802 Analog module industrial system controller

Description

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What is the difference between DTC and traditional PWM methods?
– Frequency control PWM and flux vector PWM
Traditional PWM drives use output voltage and output frequency as the primary control variables but these need to be
pulse width modulated before being applied to the
motor.
This modulator stage adds to the signal processing time and
therefore limits the level of torque and speed response
possible from the PWM drive.
Typically, a PWM modulator takes 10 times longer than DTC to
respond to actual change.
– DTC control
DTC allows the motor’s torque and stator flux to be used as
primary control variables, both of which are obtained directly
from the motor itself. Therefore, with DTC, there is no need for
a separate voltage and frequency controlled PWM modulator.
Another big advantage of a DTC drive is that no feedback device
is needed for 95 percent of all drive applications.
Why does DTC not need a tachometer or position encoder to tell it
precisely where the motor shaft is at all times?
There are four main reasons for this:
– The accuracy of the motor model (see page 29).
– Controlling variables are taken directly from the motor (see
page 29).
– The fast processing speeds of the DSP and optimum pulse
selector hardware (see page 30).
– No modulator is needed (see page 14).