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Kinetic Buffering


Murph095

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Could someone please explain this concept to me.

 

This info is from his e-mail to me

 

 

they bring in AC to a DC bus then feed into 7 inverters that feed the motors.

 

I have a customer that needs to maintain the DC bus voltage even if they have a sag on all phases up to 50% (nominal)

If they drop with the DC bus voltage below 15% of nominal, their kinetic buffering will be activated and that is something they wish to avaoid. My company has a product that can control the sags and provide ride thru, I just need to understand the kinetic buffering and how it is accomplished. Thanks

 

 

Murph

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Hello Murph

 

When the supply voltage drops, the DC Bus on the inverters will also begin to sag depending on the time constants, load etc. If the drives continue to operate at set speed, the voltage on the terminals of the motors will also drop.This can create problems if the motor are operating near their ratings. If the motors are operating at very light load, a temporary drop in voltage is not a problem.

In many drives, there is a mechanism to use the energy in the rotating loads to keep the DC bus up. If the drive decellerates faster than the natural decelleration rate of the motor and load, it will pull energy out of the load and that will lift the DC Bus voltage. This of course results in a drop in speed and that can be a problem for many processes.

In some drives, this function is an option that can be turned ON or OFF. If it is turned OFF, the drive will trip when the voltage gets too low, but the trip threshold will be below the threshold of trying to recover so it may be sufficient to turn the ride through function OFF. The actual values are dependent on the drive and are sometimes adjustable.

 

Best regards,

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