Motor And Converter Protection By Limiting The Voltage - Siemens SINAMICS G115D Operating Instructions Manual

Advanced commissioning

6.23 Motor and converter protection by limiting the voltage

6.23 Motor and converter protection by limiting the voltage
What causes an excessively high voltage?
To drive the load, an electric motor converts electrical energy into mechanical energy. If the
motor is driven by its load, e.g. due to the load moment of inertia when braking, then the
energy flow reverses: The motor temporarily operates as generator, and converts mechanical
energy into electrical energy. The electrical energy flows from the motor to the converter. If
the converter cannot output the electrical energy supplied by the motor, e.g. to a braking
resistor, then the converter stores the energy in its DC link capacitance. As a consequence,
the DC link voltage Vdc in the converter is higher.
An excessively high DC link voltage damages the converter and also the motor. As a
consequence, the converter monitors its DC link voltage - and when necessary switches off
the motor and outputs fault "DC link overvoltage".
Protecting the motor and converter against overvoltage
The Vdc_max control extends the motor ramp-down time when braking. The motor then only
feeds so much energy into the converter to cover the losses in the converter. The DC link
voltage remains in the permissible range.
The Vdc_max control is not suitable for applications where the motor is in continuous
regenerative operation, e.g. as is the case for cranes and centrifuges.
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Electrically braking the motor (Page 250)
Operating Instructions, 09/2020, FW V4.7 SP13, A5E48681219B
SINAMICS G115D distributed drive