Lenze 8400 motec - Manual (Page 167)

Lenze · 8400 motec · Reference manual · DMS 4.1 EN · 08/2013 · TD05 167
5 Motor control (MCTRL)
5.12 Braking operation/brake energy management
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
Operating mode of the inverter motor brake
During the deceleration, the speed encoder is stopped. The speed set in
C00987 is added to the
speed setpoint by means of a hysteresis-2-point DC-bus voltage controller. Here, the sign of the
current actual speed is considered. Moreover, the speed controller is stopped during overvoltage.
If the DC-bus voltage falls below a defined DC-bus voltage potential of the hysteresis controller, the
applied additive speed is cancelled and the speed encoder is enabled again.
The energy is converted into heat in the motor due to alternating instances of acceleration and
deceleration as a result of this switching operation.
[5-16] Signal flow of the "Inverter motor brake" function
• In case of an asynchronous motor, the additive speed setpoint ( C00987 ) should be 1 … 4 times
the slip of the machine:
[5-17] Formula for calculating the additive speed setpoint for an asynchronous motor
 DC-bus voltage
 Speed setpoint for motor control
0
1
nSpeedSetValue_a
C00105
C00050
C00909/1
C00909/2
Œ

C00173
0
1
C00987
0
QSP ramp
QSP
D n
Set,Add
p = number of pole pairs
n
Rat
= Rated speed of the motor
f
Rat
= Rated frequency of the motor
n
Sync
= Synchronous speed of the motor
C00987 [rpm] 1 ... 4 n
Sync
[rpm] n
Rated
[rpm] – ( ) ⋅ =
n
Sync
[rpm]
f
Rated
Hz 60 ⋅
p
-------------------------------- =

Note!
When the "inverter motor brake" function is used, torque oscillations occur which have
may have a negative effect on the service life of the components of the mechanical drive
train (e.g. gearbox).
• The extent of the occurring oscillations depends on the drive train (mass inertia,
natural frequencies, etc.) and the function setting.
• We recommend optimising the "inverter motor brake" function for an oscillation-free
operation as described in the following. Usually, this setting does not cause any
torque oscillations which affect the service life of the gearbox.
• The settings of implementing a maximum acceleration ramp are only recommended
if the inverter motor brake is used infrequently (e.g. in case of quick stop).