Input Under-Voltage Rollback - Siemens 6SR41 series Product User Manual

6.7.2

Input Under-Voltage Rollback

When the input line voltage drops below 90% of its rated value, the drive limits the amount of
power (and hence the torque) that can be delivered to the load. The maximum allowable
drive power as a function of line voltage is shown in Figure " Drive Power (Pmax) as
Function of Input Voltage Magnitude (Ed)". At 66% input voltage, the maximum drive power
is limited to 50%, and is quickly reduced to a slightly negative value at 65%. 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
drive. The output of this regulator sets the output torque limit. The NXG control provides
menu settings for the proportional and integral gains of this regulator.
Figure 6-6
Product User Manual
Operating Instructions, Version AE 12/2009, A5E01454341C
Drive Power (P ) as Function of Input Voltage Magnitude (E
max
Application and Operation
6.7 Drive Output Torque Limiting
) to the actual power flowing into the
MAX
)
d
125