Position control of AC induction motor

automatically

revolutions.

resolver

The field rotational speed is proportionnal to the frequency. By regulating the frequency with respect to an error between the setpoint and the measured speed, you force the rotation of the stator field and the rotor catches up. Please, correct me if I am wrong.

Thanks It seems reasonable. There are other ways I can imagine to do it, too. I don't know what is actually done, that's why I asked.

Jerry

You have described the control scheme for a typical open loop vector drive. While this will work for spindle drives and other variable speed work, it is wrong for a closed loop brushless DC motor. It has no zero speed stiffness. At the inner loop the drive is operating in torque mode with the current apportioned to each phase based on the rotor position. See:

In fact nothing is done as of now. One solution Artus suggested was to have an inner current loop for torque control, an intermediate frequency loop with speed feedback derived from resolver, and an outer position loop. Said like this it looks simple, but as you know, in theory, practice is the same as theory, but in practice it is not the same :) Since we have tight time schedules and limited resources we are looking for an off the shelf solution for the drive, hopefuly with position control capability or at least speed control. I will look at the link Jeff suggested, with problems being that position input is not supplied by a CAN network but by RS422 and space is limited.

position.

Thanks to your hint, I found this link:

I did not spend a whole lot of time with this l > In fact nothing is done as of now. One solution Artus suggested was > to have an inner current loop for torque control, an intermediate > frequency loop with speed feedback derived from resolver, > and an outer position loop. Said like this it looks simple, but as > you know, in theory, practice is the same as theory, but in practice > it is not the same :) > Since we have tight time schedules and limited resources we are > looking for an off the shelf solution for the drive, hopefully with > position control capability or at least speed control. I will look > at the link Jeff suggested, with problems being that position input > is not supplied by a CAN network but by RS422 and space is limited. >

The AMC drives do have an inner current loop for torque mode control, with an intermediate velocity loop, and outer position loop, all within the drive. The CAN interface should not be a problem as prepackaged controllers are available:

practice

limited.

Thanks a lot for your information.