Advanced commissioning
7.5 Motor control
The inverter has two alternative methods to control (closed loop) the motor speed:
● U/f control
● Vector control with speed controller
V/f control
Overview of the U/f control
The U/f control is a closed-loop speed control with the following characteristics:
● The inverter controls the output voltage using the V/f characteristic
● The output frequency is essentially calculated from the speed setpoint and the number of
pole pairs of the motor
● The slip compensation corrects the output frequency depending on the load and thus
increases the speed accuracy
● Not using a PI controller prevents the speed control from becoming unstable
● In applications in which greater speed accuracy is required, a closed-loop control with
load-dependent voltage boost can be selected (flux current control, FCC)
1)
In the U/f control variant, "flux current control (FCC)," the inverter controls the motor current (start-
ing current) at low speeds
Figure 7-19 Simplified function diagram of the U/f control
One function not shown in the simplified function diagram is the resonance damping for
damping mechanical oscillations. You will find the complete function diagrams 6300 et seq.
in the List Manual.
For operation of the motor with U/f control, you must set at least the subfunctions shown with
a gray background in the figure to adapt them to your application:
● V/f characteristic
● Voltage boost
Converter with control units CU240D-2
146 Operating Instructions, 04/2015, FW V4.7.3, A5E34262100B AB
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