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Vfd Regen Mode


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Hello Rahul


This is a rather open ended question!


If you can be more specific, we can give you a better answer.

As a brief overview, I assume that you are referring to an AC drive, there are two major types of regenerative operation.

  1. Brake Resistor
  2. Active front end

When you decelerate a load, you are removing kinetic energy from that load. If you decelerate slowly, the kinetic energy can be dissipated in the load as the motor slows down. As you increase the rate of deceleration, the energy removed from the load becomes too high to dissipate in the load, so the energy is transfered back into the drive. This causes the DC bus voltage to rise. If the energy transfer into the drive was unchecked and not dissipated elsewhere, the voltage would get high enough to cause damage to the drive.

One option, is to add a chopper transistor and a dump resistor. If the voltage rises above a threshold voltage, the chopper transistor turns on and dumps energy into the brake resistor. This will prevent the DC bus voltage from rising too high provided that the resistance is low enough to draw energy out of the drive faster than it is taken from the load.

Another option is to use an active front end where the input rectifier is actually and inverter stage that is able to chop up the DC voltage and feed it back into the supply. During braking, the load is treated as the supply and the mains supply is treated as a load. The active front end drive is a drive that can transfer energy in either direction.


Best regards,

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Hello Rahul


Thank you for your comments.


The difficulty with open ended questions is that it is possible to write a book as an answer and still not cover the information wanted.

As this is a free information service, there is limited time available and so we don't write books as replies.

If you are more specific with your question, the answer can be more specific. - It makes things much easier for us and more helpful for you.


Best regards,

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