ABB DO620 Analog module industrial system controller

Description

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Motor static speed accuracy: – Error between speed reference and actual value at constant load. For DTC, speed
accuracy is 10 percent of the motor slip, which with an 11
kW motor, equals 0.3 percent static speed accuracy. With
a 110 kW motor, speed accuracy is 0.1 percent without encoder (open-loop). This satisfies the accuracy requirement
or 95 percent of industrial drives applications. However, for
the same accuracy from DC drives an encoder is needed.
In contrast, with frequency controlled PWM drives, the
static speed accuracy is typically between 1 to 3 percent.
So the potential for customer process improvements is significantly higher with standard drives using DTC technology.
A DTC drive using an encoder with 1024 pulses/revolution
can achieve a speed accuracy of 0.01 percent.
– Dynamic speed accuracy: – Time integral of speed deviation when a nominal (100 percent) torque speed is applied.
DTC open-loop dynamic speed accuracy is between 0.3
to 0.4%sec. This depends on the gain adjustment of the
controller, which can be tuned to the process requirements.
With other open-loop AC drives, the dynamic accuracy is eight
times less and in practical terms around 3%sec.If we furnish
the DTC controller with an encoder, the dynamicspeed accuracy will be 0.1%sec, which matches servo drive performance.
What are the practical benefits of these performance figures?
– Fast torque response: – This significantly reduces the speed
drop time during a load transient, bringing much improved
process control and a more consistent product quality.
– Torque control at low frequencies: – This is particularlybeneficial to cranes or elevators, where the load needs to be
started and stopped regularly without any jerking. Also with
a winder, tension control can be achieved from zero through
to maximum speed. Compared to PWM flux vector drives,
DTC brings the cost saving benefit that no tachometer is
needed.
– Torque linearity: – This is important in precision applications
like winders, used in the paper industry, where an accurate
and consistent level of winding is critical.
– Dynamic speed accuracy: – After a sudden load change, the
motor can recover to a stable state remarkably fast.