16 "short-circuit braking" function, Short-circuit braking" function, 5motor control & motor settings – Lenze i700 User Manual
Page 154: Stop
5
Motor control & motor settings
5.16
"Short-circuit braking" function
154
Lenze · i700 servo inverter · Reference manual · DMS 1.5 EN · 03/2014 · TD05
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5.16
"Short-circuit braking" function
The control modes for synchronous motors provide the opportunity to use "short-circuit braking" for
the braking process.
Short-circuit braking can be
• parameterised via bit 6 in the Lenze control word (
for axis B) or
• as response to light errors.
Response of the device in the event of an error
Cases of application
• for short-circuit braking via bit 6:
• The braking energy cannot be converted into heat in a brake resistor.
• An external control wants to request short-circuit braking as e.g. an error has been detected
in the encoder system which does not permit braking via quick stop.
• for short-circuit braking as response to light errors:
• Due to an encoder error, no quick stop is possible anymore.
Functional description
The effect of the short-circuit braking on the deceleration behaviour depends on the motor features,
the effective cable length, the mass inertia and the initial value of the speed (application point).
Primarily, short-circuit braking can be used to convert a part of the kinetic energy into heat energy
which serves to unload external brake assemblies and limit position dampers.
If short-circuit braking is to be used as the only holistically effective deceleration unit, it is
recommended to verify the feasibility by tests. For this purpose, bit 6 in the Lenze control word
(
for axis B) serves to trigger the short-circuit braking. The oscilloscope function of
the »PLC Designer«/»EASY Starter« serves to record the following important objects:
• Speed: Setpoint speed (
for axis B)
• Speed: Actual speed (
for axis B)
• Phase currents U, V, W (
for axis B)
Stop!
In some constellations, it is not possible to decelerate the motor speed of a synchronous
motor to zero by means of "short-circuit braking". The braking effect cannot be
compared to the "quick stop" function where the motor is energised under optimal
conditions!
Note!
The short-circuit current is set freely according to the motor voltage (k
E
* speed) and the
internal resistance of the system. Thus, it is mandatory that the ampacity of the i700
servo inverter is oriented towards the short-circuit current to be maximally expected.
Guide value: I
max_device
(3 s) ≥ 1.5 * I
max_motor
(according to the data sheet/catalogue)
In case of a deviating assignment, a rating based on the currently possible parameters
(max. speed, max. motor current, field weakening, etc.) is required!