Motor And Inverter Protection By Limiting The Voltage - Siemens Sinamics G110M Operating Instructions Manual

6.23

Motor and inverter 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
inverter. If the inverter cannot output the electrical energy supplied by the motor, e.g. to a
braking resistor, then the inverter stores the energy in its DC link capacitance. As a
consequence, the DC link voltage Vdc in the inverter is higher.
An excessively high DC link voltage damages the inverter and also the motor. As a
consequence, the inverter monitors its DC link voltage - and when necessary switches off
the motor and outputs fault "DC link overvoltage".
Protecting the motor and inverter against overvoltage
Figure 6-61
The Vdc_max control extends the motor ramp-down time when braking. The motor then only
feeds so much energy into the inverter to cover the losses in the inverter. 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.
Distributed converter for SIMOGEAR geared motors
Operating Instructions, 09/2017, FW V4.7.9, A5E31298649B AH
Simplified representation of the Vdc_max control
Elektrically braking the motor (Page 254)
6.23 Motor and inverter protection by limiting the voltage
Advanced commissioning
269