Setting functions
8.5 Motor control
Converter with control units CU250D-2
136 Operating Instructions, 04/2014, FW V4.7, A5E34261542B AA
We recommend that you use vector control with encoder for a position-controlled axis. See
also section: Introduction, V/f control, vector control (Page 58).
U/f control sets the voltage at the motor terminals on the basis of the specified speed
setpoint.
The relationship between the speed setpoint and stator voltage is calculated using
characteristic curves. The required output frequency is calculated on the basis of the speed
setpoint and the number of pole pairs of the motor (f = n * number of pole pairs / 60, in
particular: f
max
= p1082 * number of pole pairs / 60).
The inverter provides the two most important characteristics (linear and square-law). User-
defined characteristic curves are also supported.
U/f control is not a high-precision method of controling the speed of the motor. The speed
setpoint and the speed of the motor shaft are always slightly different. The deviation
depends on the motor load.
If the connected motor is loaded with the rated torque, the motor speed is below the speed
setpoint by the amount of the rated motor slip. If the load is driving the motor (i.e. the motor
is operating as a generator), the motor speed is above the speed setpoint.
Parameter p1300 sets the characteristic curve.
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