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Affinity User Guide
125
Issue Number: 5 www.controltechniques.com
Pr 0.40 {5.12} Autotune
There are three autotune tests available in RFC mode, a stationary test, a rotating test and an inertia measurement test. A stationary autotune will
give moderate performance whereas a rotating autotune will give improved performance as it measures the actual values of the motor parameters
required by the drive. An inertia measurement test should be performed separately to a stationary or rotating autotune.
It is highly recommended that a rotating autotune is performed (Pr
0.40
set to 2).
•
A stationary autotune can be used when the motor is loaded and it is not possible to remove the load from the motor shaft. The stationary
autotune measures the stator resistance (Pr
5.17
) and transient inductance (Pr
5.24
) of the motor. These are used to calculate the current loop
gains, and at the end of the test the values in Pr
4.13
and Pr
4.14
are updated. A stationary autotune does not measure the power factor of the
motor so the value on the motor nameplate must be entered into Pr
0.43
. To perform a Stationary autotune, set Pr
0.40
to 1, and provide the
drive with both an enable signal (on terminal 31) and press the green (Hand) button.
•
A rotating autotune should only be used if the motor is unloaded. A rotating autotune first performs a stationary autotune before rotating the
motor at
2
/
3
of motor rated frequency in the direction selected for approximately 30s. During the rotating autotune the stator inductance (Pr
5.25
),
and the motor saturation breakpoints (Pr
5.29
and Pr
5.30
) are modified by the drive. The power factor is also modified for user information only,
but is not used after this point as the stator inductance is used in the vector control algorithm instead. To perform a Rotating autotune, set Pr
0.40
to 2, and provide the drive with both an enable signal (on terminal 31) and press the green (Hand) button.
•
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 motor map parameters must be set up correctly including the power factor 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.
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 Drive enable
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
).
Pr 0.38 {4.13} / Pr 0.39 {4.14} Current loop gains
The current loop gains proportional (Kp) and integral (Ki) gains control the response of the current loop to a change in current (torque) demand. The
default values give satisfactory operation with most motors. However, for optimal performance in dynamic applications 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. The values
for the current loop gains can be calculated by one of the following:
•
During a stationary or rotating autotune (see
Autotune Pr
0.40
, earlier in this table) the drive measures the stator resistance (Pr
5.17
) and
transient inductance (Pr
5.24
) of the motor and calculates the current loop gains.
•
By setting Pr
0.40
to 4 the drive will calculate the current loop gains from the values of stator resistance (Pr
5.17
) and transient inductance
(Pr
5.24
) set in the drive.
This will give a step response with minimum overshoot after a step change of current reference. The proportional gain can be increased by a factor
of 1.5 giving a similar increase in bandwidth; however, this gives a step response with approximately 12.5% overshoot. The equation for the integral
gain gives a conservative value. In some applications where it is necessary for the reference frame used by the drive to dynamically follow the flux
very closely (i.e. high speed RFC induction motor applications) the integral gain may need to have a significantly higher value.
Pr 3.42 Drive encoder filter
In RFC mode Pr
3.42
defines a filter on the output of the speed estimator which is used as the speed feedback. A filter with a 4ms time constant is
always present on the output of the speed estimator, but this filter may be extended as follows:
0 = 4ms, 1 = 8ms, 2 = 16ms, 3 = 32ms, 4 = 64ms, 5 = 128ms.
The output of the speed estimator can include some ripple, which increases as the drive passes into field weakening and the filter can be used to
remove this ripple. This is particularly useful when using standard ramp or spinning start with a low friction, high inertia load, and can prevent over
voltage trips when the drive has no braking resistor.
Pr 5.40 Spin start boost
If Pr
6.09
is set to enable the catch a spinning motor function in open-loop mode or RFC modes, this parameter defines a scaling function used by
the algorithm that detects the speed of the motor. It is likely that for smaller motors (~4kW) the default value of 1.0 is suitable, but for larger motors
this parameter may need to be increased. If the value of this parameter is too large the motor may accelerate from standstill when the drive is
enabled. If the value of this parameter is too small the drive will detect the motor speed as zero even if the motor is spinning.
NOTE
Содержание Affinity
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