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After consulting with engineers and manufacturers I still end up with the same problem. I cannot find a way to calculate this:

An elevated load goes down at a fix speed. The motor connected to it is barely able to hold it. After a few cycle we get a Buss overvoltage error

on the ac drive. We add an external braking resistor to dissipate the regenerated energy and all is o.k. BUT ...

How can we calculate this theoriticaly regenerated energy (not calculating the losses).

At 60 Hz the drive lasted 45 minutes

At 15 Hz the drive lasted 5 minutes

At 90 Hz the load crashes at the bottom for the drive cannot brake it...

The problem I have with the calculation is that Energy is divided by time to give Power and this way when I slow it more it regen. less energy altough the motor fights gravity for a longer time...

One EE sugested that I take the Tork of the system needed to equal the force (F) from gravity and with the motor speed and the kynetic energy of the load, add them up and compare to the force from gravity. Whatever is left must be the power regenerated... I end up with squared seconds... There must be a way...

Any suggestions will be greatly appreciated.

Pierre Desrochers

System Integrator

[email protected]