CHAPTER 4 - Start-up and adjustment of the drive
MANIU04.9607 GB 03/97
Page 4.16
alarm: the convertor remains enabled, but with maximum current equal to the motor rated
current, set with
P18, IN_MOT
.
On the other side, to protect the motor, besides the rated current of the motor, it is necessary
to set also the thermal time constant, with the parameter
P19, TH_MOT,
expressed in
seconds. In this way, if higher current than the rated current of the motor, but lower than the
rated current of the convertor (that could be delivered indefinitely) is required in steady-state,
the I
2
t alarm for the motor protection intervenes. The drive remains enabled, but the maximum
current limit is set in relation to the rated current of the motor.
In both cases, the I
2
t alarm will be visualized both on the 7-segment display and on the
keyboard.
To reset the drive to normal conditions, it is necessary to reset the alarm, once its possible
cause has been removed.
4.5.3 Speed mode
4.5.3.1 Adjusting of PI controller
The drive uses a PI algorithm for speed mode. It is therefore necessary to set the dynamics of
controller through parameters
P1, KP,
that represents the proportional gain of controller, and
P2, KI,
that represents the integral gain.
Basically, it can be said that when stepping up both gains, it is possible to increase the
transient response of the motor to the reference changes and to noises. This will however
also decrease the system stability margin. Moreover, the relation KP/KI,
that sets the zero of
the PI regulator, is also important for good control and stability. When increasing the KI
gain,
the drive capability to maintain the motor stopped in one position, delivering torque, is
increased.
However, it is necessary to adjust the dynamic characteristics of the system convertor-motor
to the mechanical system in which it is used. Therefore, we advise to adopt such values for
KP and KI as to guarantee a good compromise between dynamic performances and noise
sensitivity.
As well as with analog reference, the speed command can be set directly with the keyboard.
At start up, this is the default condition.
4.5.3.2 Speed analog reference: offset adjusting
The speed analog reference is drawn from the differential input related to the terminals
+RIF
(J1/7) and -RIF (J1/8).
It can be enabled with the keyboard through the flag
F2, Reference
from potentiometer,
through serial interface or with one of the two configurable inputs.
The reference enabling input (terminal SE, J1/4) can be used as START/STOP command: its
function is setting the reference to zero when it is disabled.
To use the speed analog reference it is necessary to calibrate the offset of 12-bit A/D
converter: this procedure is totally automatic and can be carried out by setting flag
F13, A/D
Converter tuning,
which will determine the value of parameters
P20, OFF_AN
and
P21,
OFFMED.
To adjust the offset, put a 0V value between the two RIF and -RIF, enable the speed
reference (SE=H) and set the flag F2: at this moment set also the flag F13, to start the offset
adjusting. The procedure stops when the keyboard shows the word
DONE,
in
correspondence with F13. Now it is possible to drive the convertor in speed mode with
analog reference.
NOTE:
lf the offset adjustment is not satisfactory (with 0V reference the motor turns slowly) it
is possible to repeat the procedure with torque enabled (terminal
RE, J1/3
): if the adjusting is
still not satisfactory, it is possible to intervene and directly modify the parameter P21,
increasing or decreasing the value to correct the motor performances.
