17.5.7 Modulation Controller
The modulation controller, which is designed as an I regulator, automatically adapts
the output value of the freque
ncy inverter to the machine behavior in the basic speed
area and in the field weakening area. If the modulation exceeds the figure set with
parameter Reference modulation 750, the field-forming current compo
the flux in the machine are reduced.
In order to make the best possible use of the voltage available, the figure selected
via parameter Operation mode 753
is put into proportion to the DC link voltage. That
means that with a high mains voltage there is also a high output volt
age available,
the drive only reaches the field weakening area later and produces a higher torque.
0 -
Usq-Control
The modulation is calculated from the ratio of torque-
forming voltage component U
sq
to the DC link voltage.
1 -
The modulation is calculated from the abs. voltage value
/ DC link voltage ratio.
The integrating part of the modulation controller is to be set via parameter Integral
time
752.
The percentage setting of the Reference modulation 750 is basically a function of the
leakage inductivity of the machine. The default value was selected such that in most
cases the remaining deviation of 5% is sufficient as a reserve range for the current
controller. For the optimization of the controller parameters, the drive is accel
with a flat ramp into the area of field weakening, so that the modu
intervenes. The limit is set via parameter Reference modulation 750. Then, the con-
trol loop can be excited with a unit step function by modifying the reference modula-
tion (change-over between 95% and 50%). By means of an oscillographed meas-
urement of the flux-forming current component on the analog output of the frequen-
cy inverter, the controlling process of the modulation controller ca
course of the signal of the flux-forming current I
sd
should reach the stationary value
after overshooting without oscillation. An oscillating of the course of the current can
be damped by increasing the integral time. The parameter Integral time 752
should
roughly correspond to the actual value Act. rotor time constant 227.
17.5.7.1 Limitation of Modulation Controller
The output signal of the modulation controller is the internal reference flux. The con-
troller output and the integrating part are limited via the parameter
lower limit 755 or the product of Rated magnetizing current 716 and Reference flux
717
. The magnetizing current parameter forming the upper limit is to be set to the
rated figure of the machine. For
the lower limit, select a value which also builds up
an adequate flux in the machine in the field weakening area. The limi
control deviation at the output of the modulation controller prevents a possible oscil-
lation of the control loop in the case of load surges. The parameter
Control deviation
limitation
756 is stated as an absolute value and acts both as a positive and a nega-
Reference Imr lower limit
Control deviation limitation
06/13 Operating Instructions ACU 239
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