Efficient Networks S120 Description of Vdcmin control without braking p1240 = 8, 9GFBPD, Qdfw

Servo control 3.14 Vdc control

can be used to maintain the DC link voltage. The threshold should be considerably higher than the shutdown threshold of the Motor Modules (recommendation: 50 V below the DC link voltage). When the power supply is reestablished, the Vdc controller is automatically deactivated and the drives approach the speed setpoint again. If the power supply cannot be reestablished, the DC link voltage collapses if the kinetic energy of the drives is exhausted with an active Vdc_min controller.

Note

You must make sure that the converter is not disconnected from the power supply. It could become disconnected, for example, if the line contactor drops out. The line contactor should have an uninterruptible power supply (UPS), for example.

Description of Vdc_min control without braking (p1240 = 8, 9)

As with p1240 = 2, 3, however, active motor braking can be prevented by reducing the DC link voltage. The effective upper torque limit must not be less than the torque limit offset (p1532). The motor does not switch to regenerative mode and no longer draws any active power from the DC link.

Description of Vdc_max control (p1240 = 1, 3)

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Figure 3-22 Switching-in/switching-out the Vdc_max control

With Infeed Modules without feedback or in the event of a power failure, the DC link voltage can increase until it reaches the shutdown threshold when drives in the DC link line-up are decelerated. To prevent the system from shutting down due to a DC link overvoltage, the Vdc_max controller can be activated for one or more drives. The Vdc_max controller is normally activated for drives that have to decelerate/accelerate high levels of kinetic energy themselves. When the overvoltage threshold in p1244 is reached (recommended setting: 50 V higher than the DC link voltage), the braking torque of the drives with an active Vdc_max controller is reduced by shifting the torque limit. In this way, the drives feed back the same amount of energy that is used as a result of losses or consumers in the DC link, thereby minimizing the braking time. If other drives for which the Vdc_max controller is not active

104	Drive Functions
	Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4