Siemens SINAMICS G120XA - Motor and Converter Protection by Limiting the Voltage; Protecting the Motor and Converter against Overvoltage; Simplified Representation of the Vdc_Max Control

6.7.5 Motor and converter protection by limiting the voltage
Overview
An electric motor converts electrical energy into mechanical energy to drive the load. If the
motor is driven by its load, e.g. by the inertia of the load during braking, the energy flow
reverses: The motor operates temporarily as a generator, and converts mechanical energy into
electrical energy. The electrical energy flows from the motor to the converter. The converter
stores the energy in its DC-link capacitors. The DC-link voltage Vdc is consequently higher in
the converter.
An excessively high DC-link voltage damages both the converter and the motor. The converter
therefore monitors its DC-link voltage and, when necessary, switches off the connected motor
and outputs the fault "DC-link overvoltage".
Function description
Protecting the motor and converter against overvoltage
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Figure 6-72 Simplified representation of the Vdc_max control
The Vdc_max control lengthens the motor ramp-down time when braking. Consequently, the
motor feeds only so much energy back into the converter to cover the losses in the converter.
The DC-link voltage remains within the permissible range.
Electrically braking the motor (Page 295)
Advanced commissioning
6.7 Drive protection
SINAMICS G120XA converter
Operating Instructions, 03/2019, FW V1.0, A5E44751205B AB 309