Operating Instructions ACU
18.5.6 Field controller
The flux-forming current component is controlled by the field controller. The guided commissioning
optimizes the parameters of the field controller by measuring the time constant and magnetizing
curve of the connected asynchronous motor. The parameters of the field controller are selected such
that they can be used without changes in most applications. The proportional and the integrating
part of the field controller are to be set via parameters Amplification 741 and Integral Time 742.
Please note that any changes of the field controller should only be made in the base speed range.
If the field controller must be optimized, set the Field Controller Integral Time 742 = Act. Rotor
Time Constant 227 / 2, i.e. half the rotor time constants. In most applications, this change will be
sufficient.
If additional optimization is required, please proceed as follows:
First set the output frequency (e.g. via reference frequency) such that the actual value Modulation
223 = 80…90 % Reference Modulation 750.
Now, change parameter Reference Flux 717 from 100 % to 90 %. While doing so, oscillograph I
sd
.
The course of the signal of the flux-forming current I
sd
should reach the stationary value after
overshooting without oscillation.
Adjust parameters Amplification 741 and Integral Time 742 according to the application
requirements.
Change the Reference Flux 717 back to 100 % and repeat the reference flux jump, while analyzing
the changes by means of oscillography. Repeat these steps if necessary.
If a quick transition into field weakening is necessary for the application, the integral time should be
reduced.
For good dynamic behavior, choose a relatively high value for Amplification 741 of the controller.
Note that high overshoot is necessary for good control behavior in controlling of a load with low-
pass behavior, for example a 3-phase machine.
Parameter Reduction Factor Flux 778 reduces the stall current when a stopping behavior is
selected with “Stop” function. This stopping behavior is selected if Parameter Operation Mode 630
is set to 2x (20 … 27 – “R->0, Stop, … ”) or x2 (2, 12, 22, 32, 42, 52, 62, 72 – “ … , R->0, Stop”).
The stopping behavior is described in Chapter "".
In these operation modes, the setting for Reduction Factor Flux 778 will be effective once the time
set in parameter Holding Time 638 has elapsed. The resulting stall flux is calculated from the
factors Reference Flux 717 and Reduction Factor Flux 778. After a start command, the drive will
start immediately and the flux will increase to the reference flux while the drive is running.
Due to the reduced flux, a higher torque-forming current component Isq is needed when the drive is
starting. The time required to reach the reference flux can be influenced via parameter Ref. Isd
Upper Limit 743. This parameter is set to the rated motor current during guided commissioning.
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