Lenze 8400 - Manual (Page 270)

5 Motor control (MCTRL)
5.13 Braking operation/brake energy management
270
Lenze · 8400 protec HighLine · Reference manual · DMS 3.0 EN · 03/2013 · TD05
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5.13 Braking operation/brake energy management
When braking electrical motors, the kinetic energy of the drive train is fed back regeneratively to the
DC bus. This energy results in a boost of the DC-bus voltage.
• Several different strategies can serve to avoid DC-bus overvoltages:
• Use of a brake resistor
• Stopping of the ramp function generator if brake chopper threshold exceeded (RFG_Stop)
• Use of the "inverter motor brake" function
• Combination of the above named options
• In the case of inverters with a 3-phase supply, the following is also possible:
• Coupling of the inverters in a DC-bus connection
• Recovery of regenerative energy with a regenerative module
Using the integrated brake chopper
We recommend to use the brake chopper (brake transistor) which is integrated into the controller
for the braking operation, regardless of the selected motor mode.
• Connect the required brake resistor to the R
B1
and R
B2
terminals of the controller.
• In C00175 , a ramp function generator stop (FB L_NSet_1 ) can be set for instances when the
brake resistor is controlled. This prevents overvoltage deactivation in the case of short
deceleration times.  Selecting the response to an increase of the DC-bus voltage ( 273)

Stop!
If the connected brake resistor is smaller than required, the brake chopper can be
destroyed!
• Appropriate protective measures are described in subchapter " Avoiding thermal
overload of the brake resistor ". ( 278)
If no brake resistor or regenerative module is used, the overvoltage switch-off ("OU")
may respond, e.g. in the case of short deceleration times during feedback operation.
 Error messages of the operating system ( 580)

Note!
The brake transistor will be switched off if it remains switched on for a period of 4
seconds.
• If the DC-bus voltage falls under the brake chopper threshold for a short time again,
the brake transistor can switch on again for a maximum of 4 seconds, without
interruption.
• This protective function is used to prevent the brake chopper from being switched on
permanently due to e.g. too high voltages at all times or incorrect interconnection of
the bBrakeChopperOn signal (from software version V12.00.00) .