Drive Output Torque Limiting; Input Under-Voltage Rollback - Siemens SINAMICS PERFECT HARMONY GH180 Function Manual

Operating the Control

7.10 Drive Output Torque Limiting

7.10 Drive Output Torque Limiting
The drive uses measured voltages and currents to implement rollback conditions. Under one or
more of these conditions, the drive will continue to operate, but at a lower output torque or
current level. An output torque limit will force the motor and the drive to go into speed rollback,
during which speed is reduced until the torque demanded by the load falls below the torque
limit. Rollbacks are triggered by various conditions and are described in the following sections.
7.10.1

Input Under-Voltage Rollback

When the input line voltage drops below 90% of its rated value, the drive limits the amount of
power, and thus torque, that can be delivered to the load. The maximum allowable drive power
as a function of line voltage is shown in the figure below. At 66% input voltage, the maximum
drive power is limited to 50%, and is quickly reduced to a slightly negative value at 65%. This is
the regenerative limit. This limit forces the drive to absorb power from the motor and maintain
the cell DC-bus voltages, in case the input voltage recovers during MV ride-through. The limit is
implemented as an inverse function of speed to maintain constant power flow to the cell DC-
bus.
A regulator is implemented to match the maximum drive power (P
flowing into the drive. The output of this regulator sets the output torque limit.
Figure 7-21
Parameters for Proportional and Integral Gains of the Regulator
Refer to Input Protect Menu (7000) in Section Options for Drive Protect Menu (7) of
Chapter Parameter Assignment / Addressing for parameters associated with this function.
• Undervoltage prop gain (7060) represents the proportional gain of this regulator.
• Undervoltage integ gain (7070) represents the integral gain of this regulator.
• An under-voltage rollback condition is indicated by the drive, by displaying UVLT on the
keypad and in the ToolSuite.
212
Drive Power (P ) as Function of Input Voltage Magnitude (E
max
) to the actual power
max
)
d
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