5motor control (mctrl) – Lenze 8400 StateLine User Manual
Page 150
5
Motor control (MCTRL)
5.5
V/f characteristic control - energy-saving (VFCplusEco)
150
Lenze · 8400 StateLine · Reference manual · DMS 12.0 EN · 06/2014 · TD05/TD14
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5.5.4.1
Improving the behaviour at high dynamic load changes
Due to the voltage reduction executed via the cosϕ control, the motor may stall in the Lenze setting
at high dynamic load torque changes. This is caused by the flux reduction and the connected
reduction of the stalling torque of the motor current:
It generally applies that when the output voltage is divided in halves, the maximum torque is
approx. reduced by the factor 4. A reduction by the factor 5 reduces the torque to approx. 15 ... 50 %
of the rated torque.
The minimum voltage and thus the maximum influence access of the Eco function on the output
voltage can be defined in
. With full influence of the Eco function, the following stalling
torque can be ensured depending on the setting in
An adaptation of the minimum voltage V/f (
) improves the stability in case of load impulses.
• In the Lenze setting, the minimum voltage V/f is set to 20 % for the highest energy optimisation.
This setting serves to respond to load torques if these amount to approx. 25 % of the rated
torque or occur with low dynamics.
• An increase of the minimum voltage V/f to 70 % permits to apply a dynamic load impulse from
0 to 100 % rated motor torque without the motor stalling. This reduces the energy optimisation
to be achieved by approx. 75 %.
• A further increase of the stability at still higher dynamic load impulses can be achieved by a
further increase of the minimum voltage V/f, but means a further loss in energy optimisation.
V
Motor
= display in
V
Reduction
Minimum voltage V/f
Maximum torque
100 %
160 % … 250 % M
rated
70 %
80 % … 130 % M
rated
50 %
40 % … 70 % M
rated
20 %
15 % … 50 % M
rated
Note!
In case of applications with very high dynamic sudden load variations from the unloaded
operation, this motor control mode should not be used or the energy optimisation
should be switched off, since a motor stalling cannot be excluded.
• The energy optimisation can be switched off by setting the minimum voltage V/f
(
) to 100 %. Then, the behaviour corresponds to the V/f characteristic control
(VFCplus) with linear characteristic.
•
From version 13.00.00
, the energy optimisation can be switched off via the
bVfcEcoDisable process signal if a dynamic load change is known to take place.
M
Max(t)
M
Stalling
U
Motor(t)
2
U
Motor(t)
U
Reduction
–
(
)
2
-------------------------------------------------------------
⋅
=
with M
Stalling
1.6 ... 2.5 M
Rated_motor
⋅
=