Configuration
Function blocks
Internal motor control with V/f characteristic control (MCTRL1)
8
8.2
8.2.6
8.2-47
EDSVF9333V EN 3.0-06/2005
The speed of an asynchronous machine decreases when being loaded. This
load-dependent speed drop is called slip. By setting C0021 the slip can be
partly compensated.
In the V/f characteristic control mode the slip compensation is only active at
operation without feedback (C0025 = 1).
V/fcharacteristiccontrol
The slip compensation (C0021) is automatically calculated from the rated
motor speed (C0087) and the rated m otor frequency (C0089). The entered
slip constant [%] is the rated slip of the motor in [%] relating to the
synchronous speed of the motor.
ƒ Calculating the slip compensation and entering it into C0021:
s =
n
rsyn
− n
r
n
rsyn
⋅ 100 %
n
rsyn
=
f
r
⋅ 60
p
E Slip constant (C0021) [%]
n
rsyn
Synchronous motor speed [min
-1
]
n
r
Rated motor speed according to
motor nameplate [min
-1
]
f
r
Rated motor frequency according to
motor nameplate [Hz]
p Number of motor pole pairs (1, 2, 3,
...)
ƒ If required, the slip compensation can be adapted manually:
– If C0021 is set too high, the drive may get unstable.
– With cyclic load impulses (e. g. centrifugal pump) a smooth motor
characteristic is achieved by smaller values in C0021 (possibly
negative values)
– Parameterise C0078 (filter time for the slip compensation) if you
want to change the motor response time to load changes
(dynamic ↔ slow).
ƒ The actual speed is output as an analog signal (in [%] of n
max
(C0011))
to MCTRL-NACT.
Note!
When operating synchronous or reluctance motors, C0021 must
be set to 0.
If the motor may only rotate in one direction, you can limit the output
voltage generation to one direction of rotation via C0909.
Code Description
C0909 = 1 The motor rotates in both directions
C0909 = 2 Motor rotates clockwise, ”positive direction of rotation”
(View of the motor shaft)
C0909 = 3 Motor rotates counter-clockwise, ”negative direction of rotation”
(View of the motor shaft)
Slip compensation
Inhibiting the direction o f
rotation
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