Lenze 8400 motec - Manual (Page 112)

5 Motor control (MCTRL)
5.6 V/f characteristic control - energy-saving (VFCplusEco)
112 Lenze · 8400 motec · Reference manual · DMS 4.1 EN · 08/2013 · TD05
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5.6.4.1 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
in case of high dynamic load changes (dynamic load impulse from 0 to more than 50 % rated motor
torque).
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.
With this setting, a dynamic load impulse from 0 to approx. 50 % rated motor torque can be
applied without the motor stalling.
• 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.
5.6.4.2 Adapting the slope limitation for lowering the Eco function
The ramp set in C00982 for voltage reduction serves as slope limitation in order to prevent that
voltage is suddenly applied to the motor when the Eco function is deactivated. Otherwise, the
overvoltage limitation (Imax, Clamp) would be activated.
• This ramp is, depending on the device, pre-initialised to approx. the triple rotor time constant.
An adaptation of this parameter is not required.
When the Eco function is switched off, a quick reaction (high dynamic performance) is required, but
with a low current overshoot and a small torque jump. Thus, the Lenze setting of C00982 is a
compromise regarding the switch-off of the Eco function (motor voltage sub=0).
• To increase the dynamics when switching off the Eco function:
Reduce  setting in C00982 .
(Current compensation actions increase when the Eco function is switched off.)
• In order to reduce current compensation actions when switching off the Eco function:
Increase  setting in C00982 .
(The dynamics when switching off the eco function is reduced)

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.