Changes - Lenze L-force HighLine C 8400 Series Reference Manual

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:
M
=
Max(t)
V = display in
Motor
V = display in
Reduction
It generally holds true that halving the output voltage results in a reduction of the
maximum torque by a factor of approx. 4. A reduction by a factor of 5 results in a reduction
of 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 C00977. With full influence of the Eco function, the
following stalling torque can be ensured depending on the setting in C00977:
An adaptation of the minimum voltage V/f (C00977) 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.

Note!
The energy optimisation can be switched off by setting the minimum voltage
V/f (C00977) to 100 %. Then, the behaviour corresponds to the V/f characteristic
control (VFCplus) with linear characteristic.
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.
Firmware ≤ 11.00 - DMS 6.0 EN - 10/2011
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V/f characteristic control - energy-saving (VFCplusEco)
2
U
Motor(t)
M
⋅
------------------------------------------------------------ -
Stalling
( U U
–
Motor(t) Reduction
C00052
C00978
Minimum voltage V/f
(C00977)
100 %
70 %
50 %
20 %
L
8400 HighLine C | Reference manual
with M 1.6 ... 2.5 M
=
Stalling
2
)
Maximum torque
160 % ... 250 % M
80 % ... 130 % M
40 % ... 70 % M
15 % ... 50 % M
Motor control (MCTRL)
⋅
Rated_motor
rated
rated
rated
rated
175