Malfunctions Not Indicated by a Fault
3-21
The measured motor voltage
above base speed does not
remain constant.
When the actual motor velocity exceeds
the base speed of the motor, the
armature voltage continues to vary
proportional to velocity.
Verify that the field weakening enable, bit 1 of parameter 627
“Flux Mode Select” is set to 1. This bit must be set if constant
horsepower operation is desired.
When the actual motor velocity exceeds
the base speed of the motor, the
armature voltage varies, but not directly
proportional to velocity. The load on the
motor is relatively constant.
•
Verify that the Field Flux Tune has been executed under
Autotune control. This must be performed prior to operating the
drive above base speed to ensure that the field control
parameters have been set to reflect the flux characteristics of
the motor. Autotune will calibrate the field weakening
parameters 677 to 685 and enter them into the parameter
table.
In addition, the CEMF regulator must also be tuned. The CEMF
regulator varies the field reference based on the CEMF of the
motor being measured. The CEMF regulator will adjust the field
reference during operation to maintain a constant Armature
voltage. The response of this regulator is controlled by parameter
672 “KI Flux” and parameter 673 “KP Flux”. These parameters
control the gain of the CEMF regulator. Setting parameter 687
“CEMF Preload” to zero and parameter 627 “Flux Mode Select” bit
5 (CEMF Set) to 1 will disable the CEMF regulator. If bits 4 (Hold)
and 5 (Set) in parameter 627 are both set to 0, the CEMF regulator
is automatically enabled and uses parameter 610 “Rated Motor
Volt” as the reference.
•
Verify that the external CEMF regulator control, bit 3 of
parameter 627 “Flux Mode Select” is set to 0. If this bit is set to
1, parameter 160 “CEMF Ref” will be used to determine the
CEMF regulator reference, instead of the rated motor voltage
parameter. Also verify that bits 4 and 5 are set to zero under
normal operation. If bit 4 is set to 1 the CEMF regulator will
hold its output to the last value before the bit was set. If bit 5 is
set to 1 the output of the CEMF regulator will be reset to the
value specified in parameter 687 “CEMF Reg Preload”.
Parameter 686 “Fld Weaken Speed” determines the velocity at
which the field weakening function will become active.
The measured motor voltage
above base speed does not
remain constant.
(continued)
When the actual motor velocity exceeds
the base speed of the motor, the
armature voltage varies directly with the
load on the motor.
•
If the armature voltage changes significantly (greater than 5%)
with an increasing load, the armature resistance compensation
is too high. Reduce parameter 614 “Arm Resistance”. If
armature voltage increases significantly with an increasing
load, parameter 614 is too low. A typical range is 3 to 10%.
TP25-Field Current Feedback can be used to monitor the field
current as sensed by the current transformer FCT. This signal is
scaled so that 3VDC = full rating of the bridge as determined by
the jumper setting of J1 on the feedback board or the PSI/Switcher
based on the HP rating. Either an oscilloscope (preferred) or a
DVM can be used to monitor this signal with respect to AGND
(TP57). The waveform in Figure 3-12 shows the typical waveform
of field current feedback.
Field Current Control Malfunctions
Malfunction
Symptom
Solution
!
ATTENTION:
Extreme care must be used when probing the
test points on any board. Improper techniques may result in
damage to the circuit and personal injury. Do Not attempt probe
tests that are not listed here. Damage to extremely sensitive
circuits may cause unpredictable drive operation and unintended
motor rotation.
Aotewell Ltd industry-mall.net
www.aotewell.com
sales@aotewell.com
www.aotewell.com