drive ramping with a plc

[AJW]

I have done this before, but always looking for a better way. The application is: I have 3 AC inverters operating in open loop vector mode. I know the answer, but is cost related. Using encoders, or servos would be my way to. However it is what it is. I need to ramp 3 VFD's. One will always run a the speed set point the other 2 (followers) will be at an adjustable %, plus or minus, of the speed setpoint. I also have adjustmnet for the Accel and Decel time. I calculate the ramp rate base on the speed set point and the accel/decel times on a time base of 100ms. The problem I have always had is the followers do not get to 0 speed at the same time the main does. I have a solution I am working on and will share at a later date. This post is already long. I am just looking for ideas to see how they compare to mine.

Thanks

 

[Lancie1]

The problem I have always had is the followers do not get to 0 speed at the same time the main does.

Yes, the Followers have farther to go - a larger change to make from the setpoint, so (if their accel and deaccel times are the SAME as the MAIN drive) they will always arrrive last.

To make all 3 drives arrive at final setpoints at the same time, the accel and decel parameter settings of the main must be longer (recommended method), or the Follower set times must be shorter.