Emerson Digitax ST User Manual Download Page 169

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Digitax ST User Guide

169

Issue Number: 5

4: Speed control with torque feed-forward

The drive operates under speed control, but a torque value may be
added to the output of the speed controller. This can be used to improve
the regulation of systems where the speed loop gains need to be low for
stability.

12.22.5 Stop modes

Only one stopping phases exists and the ready state is entered as soon
as the single stopping action is complete.

The motor can be stopped with position orientation after stopping. This
mode is selected with the position controller mode parameter (Pr

13.10

When this mode is selected Pr

6.01

has no effect.

When this bit is set the drive remains active even when the run
command has been removed and the motor has reached standstill.

12.22.6 Line power supply loss modes

0: diS

There is no line power supply loss detection and the drive operates
normally only as long as the DC bus voltage remains within specification
(i.e. >Vuu). Once the voltage falls below Vuu an under-voltage ‘UV’ trip
occurs. This will reset itself if the voltage rises above Vuu Restart, as
stated in the table below.

1: StoP

The speed reference is set to zero and the ramps are disabled allowing
the drive to decelerate the motor to a stop under current limit. If the line
power supply is re-applied while the motor is stopping any run signal is
ignored until the motor has stopped. If the current limit value is set very
low level the drive may trip UV before the motor has stopped.

2: ridE.th

The drive detects line power supply loss when the DC bus voltage falls
below Vml

. The drive then enters a mode where a closed-loop

controller attempts to hold the DC bus level at Vml

. This causes the

motor to decelerate at a rate that increases as the speed falls. If the line
power supply is re-applied it will force the DC bus voltage above the
detection threshold Vml

and the drive will continue to operate normally.

The output of the line power supply loss controller is a current demand
that is fed into the current control system and therefore the gain Pr

4.13

and Pr

4.14

must be set up for optimum control. See parameters Pr

4.13

and Pr

4.14

for set-up details.

The following table shows the voltage levels used by drives with each
voltage rating.

* Vml

is defined by Pr

6.48

. The values in the table above are the

default values.

The line power supply loss detection level can be adjusted using this
parameter. If the value is reduced below the default value, the default
value is used by the drive. If the level is set too high, so that the line
power supply loss detection becomes active under normal operating
conditions, the motor will coast to a stop.

The Kp and Ki gains are used in the voltage based current controller.
The default values give satisfactory operation with most motors.
However it may be necessary to change the gains to improve the
performance. The proportional gain (Pr

4.13

) is the most critical value in

controlling the performance. Either the value can be set by auto-tuning
(see Pr

5.12

) or it can be set by the user so that

4.13

= Kp = (L / T) x (I

/ V

) x (256 / 5)

Where:

T is the sample time of the current controllers. The drive
compensates for any change of sample time, and so it should be
assumed that the sample time is equivalent to the lowest sample
rate of 167

L is the motor inductance. For a servo motor this is half the phase to
phase inductance that is normally specified by the manufacturer. For
an induction motor this is the per phase transient inductance (

This is the inductance value stored in Pr

5.24

after the autotune test

6.01

Stop mode

Txt

COASt (0), rP (1), no.rP (2)

no.rP (2)

Stopping Mode

Action

0: Coast

Inhibits the inverter