Operating Instructions ACU
18.5 Functions of field-oriented control
The field-oriented control systems are based on a cascade control and the calculation of a complex
machine model. In the course of the guided commissioning, a map of the connected machine is
produced by the parameter identification and transferred to various parameters. Some of these
parameters are visible and can be optimized for various operating points.
18.5.1 Current controller
The inner control loop of the field-oriented control comprises two current controllers. The field-
oriented control thus impresses the motor current into the machine via two components to be
controlled.
This is done by:
controlling the flux-forming current value I
sd
controlling the torque-forming current value I
sq
By separate regulation of these two parameters, a decoupling of the system equivalent to an
externally excited direct current machine is achieved.
The set-up of the two current controllers is identical and enables joint setting of amplification as well
as the integral time for both controllers. Parameters Amplification 700 and Integral Time 701 are
available for this. The proportional and integration and component of the current controllers can be
switched off by setting the parameters to zero.
The guided commissioning has selected the parameters of the current controller in such a way that
they can be used without having to be changed in most applications.
If, in exceptional cases, an optimization of the behavior of the current controllers is to be done, the
reference value jump during the flux-formation phase can be used for this. With suitable
parameterization, the reference value of the flux-forming current components leaps to Current
during Flux-Formation 781 and, after elapsing of Max. Flux-Formation Time 780, then changes in
a controlled way to the magnetizing current. The operating point necessary for the adjustment
demands the setting of parameter Minimum Frequency 418 to 0.00 Hz, as the drive is accelerated
after magnetizing. The measurement of the jump reply, which is defined by the ratio of the currents
mentioned, should be done in the motor supply line by means of a measuring current transformer of
a sufficient bandwidth.
The internally calculated actual value for the flux-forming current component cannot
be output via the analog output for this measurement as the time resolution of the
measurement is not sufficient.
To set the parameters of the PI controller, the Amplification 700 is increased first until the actual
value overshoots distinctly during the control process. Now, the amplification is reduced to about
fifty percent again and then the Integral Time 701 is synchronized until actual value overshoots
slightly during the control process.
The settings of the current controllers should not be too dynamic in order to ensure a sufficient
reserve range. The control tends to increased oscillations if the reverse range is reduced.
The dimensioning of the current controller parameters by calculation of the time constant is to be
done for a switching frequency of 2 kHz. For other switching frequencies, the values are adapted
internally so that the setting can remain unchanged for all switching frequencies. The dynamic
properties of the current controller improve if the switching and scanning frequency increases.
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