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6.12.5 Volts-per-hertz control mode
July 2013
In volts-per-hertz control mode (U/f control mode), the motor is speed-
controlled in an open loop. The motor voltage increases in proportion to
frequency up to the break (= threshold rpm for field weakening). Then the
motor voltage remains constant (= rated voltage of motor); only the frequency
continues to increase.
If the spindle reaches the maximum current due to excessive load, the error
message C380 Motor <Spindle 1/2> not controllable appears. For the
maximum current, the value from either the motor table or the power-module
table of the drive (whichever is lower) applies.
U
M
U
N
The maximum speed in the volts-per-hertz control mode corresponds to the
maximum speed in closed loop operation.
To drive a motor in the volts-per-hertz control mode :
In the motor table, enter for your motor in the column Motor model (TYPE)
UASM, in the column Encoder line count (STR.) the value 0, in the column
Type of encoder (SYS) the value 0 and in the column Maximum temperature
[°C] T-MAX the value 255.
The machine parameters for current controller (MP24xx.y) and speed
controller (MP25xx.y, MP 26xx.y) are nonfunctional.
The acceleration and breaking ramp (MP341x) must be set so that the
maximum current is not exceeded.
Since during volts-per-hertz (U/f) control mode no speed encoder is used,
W322 = 0 (actual speed value) supplies the value 0:
Module 9164 can determine the actual speed value while the spindle is
running, but not during the acceleration and braking phases.
Note
The oscilloscope shows the actual current instead of the nominal current
(I NOML), since there is no nominal current with U/f components.
6.12 Spindle
f
break
f
M
967
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