58
Digitax ST User Guide
Issue: 5
* only applicable to Modbus RTU mode
This parameter can be changed via the drive keypad, via a Solutions
Module or via the comms interface itself. If it is changed via the comms
interface, the response to the command uses the original baud rate. The
master should wait at least 20 ms before send a new message using the
new baud rate.
Used to define the unique address for the drive for the serial interface.
The drive is always a slave.
Modbus RTU
When the Modbus RTU protocol is used addresses between 0 and 247
are permitted. Address 0 is used to globally address all slaves, and so
this address should not be set in this parameter
ANSI
When the ANSI protocol is used the first digit is the group and the
second digit is the address within a group. The maximum permitted
group number is 9 and the maximum permitted address within a group is
9. Therefore, Pr
0.37
is limited to 99 in this mode. The value 00 is used
to globally address all slaves on the system, and x0 is used to address
all slaves of group x, therefore these addresses should not be set in this
parameter.
These parameters control the proportional and integral gains of the
current controller used in the open loop drive. The current controller
either provides current limits or closed loop torque control by modifying
the drive output frequency. The control loop is also used in its torque
mode during line power supply loss, or when the controlled mode
standard ramp is active and the drive is decelerating, to regulate the flow
of current into the drive.
There are five autotune tests available, a short low speed test, a normal
low speed test, an inertia measurement test, a stationary test and a
minimal movement test. A normal low speed should be done where
possible as the drive measures the stator resistance and inductance of
the motor, and from these calculates the current loop gains. An inertia
measurement test should be performed separately to a short low speed
or normal low speed autotune.
•
A short low speed test will rotate the motor by 2 electrical revolutions
(i.e. up to 2 mechanical revolutions) in the forward direction, and
measure the encoder phase angle. The motor must be free from
load for this test.
•
A normal low speed test will rotate the motor by 2 electrical
revolutions (i.e. up to 2 mechanical revolutions) in the forward
direction. This test measures the encoder phase angle and updates
other parameters including the current loop gains. The motor must
be free from load for this test.
•
The inertia measurement test can measure the total inertia of the
load and the motor. This is used to set the speed loop gains and to
provide torque feed forward when required during acceleration.
During the inertia measurement test the motor speed changes from
1
/
3
to
2
/
3
rated speed in the forward direction several times. The
motor can be loaded with a constant torque load and still give an
accurate result, however, non-linear loads and loads that change
with speed will cause measurement errors.
•
The stationary test only measures the motor resistance and
inductance, and updates the current loop gain parameters. This test
does not measure the encoder phase angle so this test needs to be
done in conjunction with either the short low speed or minimal
movement tests.
•
The minimal movement test will move the motor through a small
angle to measure the encoder phase angle. This test will operate
correctly when the load is an inertia, and although a small amount of
cogging and stiction is acceptable, this test cannot be used for a
loaded motor.
To perform an autotune, set Pr
0.40
to 1 for a short low speed test, 2 for
a normal low speed test, 3 for an inertia measurement test, 4 for a
stationary test or 5 for a minimal movement test, and provide the drive
with both an enable signal (on terminal 31) and a run signal (on terminal
26 or 27).
Following the completion of an autotune test the drive will go into the
inhibit state. The drive must be placed into a controlled disable condition
before the drive can be made to run at the required reference. The drive
can be put in to a controlled disable condition by removing the Safe
Torque Off signal from terminal 31, setting the drive enable parameter
Pr
6.15
to OFF (0) or disabling the drive via the control word (Pr
6.42
&
Pr
6.43
).
Setting Pr
0.40
to 6 will cause the drive to calculate the current loop
gains based on the previously measured values of motor resistance and
inductance. The drive does apply any voltage to the motor during this
test. The drive will change Pr
0.40
back to 0 as soon as the calculations
are complete (approximately 500 ms).
For further information refer to section
This parameter defines the required switching frequency. The drive may
automatically reduce the actual switching frequency (without changing
this parameter) if the power stage becomes too hot. A thermal model of
the IGBT junction temperature is used based on the heatsink
temperature and an instantaneous temperature drop using the drive
output current and switching frequency. The estimated IGBT junction
temperature is displayed in Pr
7.34
. If the temperature exceeds 145
°
C/
170
°
C (variant dependant) the switching frequency is reduced if this is
possible (i.e >3 kHz). Reducing the switching frequency reduces the
drive losses and the junction temperature displayed in Pr
7.34
also
reduces. If the load condition persists the junction temperature may
continue to rise again above 145
°
C/170
°
C (variant dependant) and the
drive cannot reduce the switching frequency further the drive will initiate
an ‘O.ht1’ trip. Every second the drive will attempt to restore the
switching frequency to the level set in Pr
0.41
.
0.36 {11.25}
Serial comms baud rate
RW
Txt
US
Ú
300 (0), 600 (1), 1200 (2),
2400 (3), 4800 (4), 9600 (5),
19200 (6), 38400 (7),
57600 (8)*, 115200 (9)*
Ö
19200 (6)
0.37 {11.23}
Serial address
RW
Uni
US
Ú
0 to 247
Ö
1
0.38 {4.13}
Current loop P gain
RW
Uni
US
Ú
0 to 30,000
Ö
200 V drive: 75
400 V drive: 150
0.39 {4.14}
Current loop I gain
RW
Uni
US
Ú
0 to 30,000
Ö
200 V drive: 1,000
400 V drive: 2,000
0.40 {5.12}
Autotune
RW
Uni
Ú
0 to 6
Ö
0
0.41 {5.18}
Maximum switching frequency
RW
Txt
RA
US
Ú
3 (0), 4 (1), 6 (2), 8 (3), 12 (4)
Ö
6 (2)
