Digitax ST User Guide
69
Issue: 5
8 Optimization
This chapter takes the user through methods of optimizing the product set-up, maximizing performance. The auto-tuning features of the drive simplify
this task.
8.1 Motor map parameters
8.1.1 Motor control
Pr 0.46 {5.07} Motor rated current
Defines the maximum motor continuous current
The motor rated current parameter must be set to the maximum continuous current of the motor. The motor rated current is used in the following:
•
Current limits
•
Motor thermal overload protection
Pr 0.42 {5.11} Motor number of poles
Defines the number of motor poles
The motor number of poles parameter defines the number of electrical revolutions in one whole mechanical revolution of the motor. This parameter
must be set correctly for the control algorithms to operate correctly. When Pr
0.42
is set to "Auto" the number of poles is 6.
Pr 0.40 {5.12} Autotune
There are five autotune tests available, a short low speed test, a normal low speed test, an inertia measurement test, a stationary test to set up
current controller gains and a minimal movement phasing 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 direction selected. The drive
applies rated current to the motor during the test and measures the encoder phase angle (Pr
3.25
). The phase angle measurement is taken when
the motor has stopped at the end of the test, therefore there must be no load on the motor when it is at rest for the correct angle to be measured.
This test takes approximately 2 seconds to complete and can only be used where the rotor settles to a stable position in a short time. To perform a
short low speed autotune, set Pr
0.40
to 1, and provide the drive with both an enable signal (on terminal 31) and a run signal (on terminal 26 or 27).
•
A normal low speed test will rotate the motor by 2 electrical revolutions (i.e. up to 2 mechanical revolutions) in the direction selected. The drive applies
rated current to the motor during the test and measures the encoder phase angle (Pr
3.25
). The phase angle measurement is taken when the motor
has stopped at the end of the test, therefore there must be no load on the motor when it is at rest for the correct angle to be measured. The motor
resistance (Pr
5.17
) and inductance (Pr
5.24
) are then measured, and the values are used to set up the current loop gains (Pr
0.38
{
4.13
} and Pr
0.39
{
4.14
}). The whole test takes approximately 20 seconds and can be used with motors that take time to settle after the rotor has moved. During the
motor inductance measurement the drive applies current pulses to the motor that produces flux that opposes the flux produced by the magnets. The
maximum current applied is a quarter of rated current (Pr
0.46
). This current is unlikely to affect the motor magnets, however, if this level of current
could permanently de-magnetise the magnets the rated current should be set to a lower level for the tests to avoid this. To perform a normal low
speed autotune, set Pr
0.40
to 2, and provide the drive with both an enable signal (on terminal 31) and a run signal (on terminal 26 or 27).
•
The inertia measurement test can measure the total inertia of the load and the motor. This is used to set the speed loop gains (see
Speed loop
gains
) and to provide torque feed-forwards when required during acceleration.
During the inertia measurement test the drive attempts to accelerate the motor in the direction selected up to
3
/
4
x rated load rpm and then back to
standstill. The drive uses rated torque/16, but if the motor cannot be accelerated to the required speed the drive then increases the torque progressively
to x
1
/
8
, x
1
/
4
, x
1
/
2
and x1 rated torque. If the required speed is not achieved on the final attempt the test is aborted and a tunE1 trip is initiated. If the test
is successful the acceleration and deceleration times are used to calculate the motor and load inertia which is then written to Pr
3.18
. The value of the
value of motor torque per amp in Pr
5.32
and the motor rated speed in Pr
5.08
must be set up correctly before performing an inertia measurement test.
To perform an Inertia measurement autotune, set Pr
0.40
to 3, and provide the drive with both an enable signal (on terminal 31) and a run signal
(on terminal 26 or 27).
•
The stationary test to set up current controller gains measures the stator resistance and the transient inductance of the motor, calculates the
current loop gains and updates the current loop gain parameters. This test does not measure the encoder phase angle. This test should only be
performed when the correct phasing angle has been set in Pr
0.43
. If the phasing angle is not correct the motor may move and the results may
be incorrect. To perform a stationary test to set up current controller gains, set Pr
0.40
to 4, and provide the drive with both an enable signal (on
terminal 31) and a run signal (on terminal 26 or 27).
•
A minimal movement phasing test can measure the encoder phase offset by moving the motor through a small angle. Short current pulses are
applied to the motor to produce a small movement and then to move the motor back to the original position. The size and length of the pulses
are gradually increased (up to a maximum of motor rated current) until the movement is approximately at the level defined by Pr
5.38
electrical
degrees. The resulting movements are used to estimate the phase angle. To perform a minimal movement phasing test, set Pr
0.40
to 5, 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
).
0
0
Summary of Contents for Digitax ST
Page 1: ...User Guide AC variable speed drive for servo motors Part Number 0475 0001 05 Issue 5 ...
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