Hello

What needs to be concerned when I use a PLC to control high power variable frequency drive by program? I want the VFD to control a 37KW fan, is it power off both of the vfd drive and fan at the same time directly? How about the feedback current?

PLC control variable frequency drive does not relate to the power size.

For the stop mode it depends on fan, it's decelerate parking or free parking, or needs additional braking device.
Generally the fan does not have special requirements they are decelerate parking or free parking.
For free parking there is no special requirements, directly power off the vfd drive and fan, also nothing special for the variable frequency drive, and there is no feedback current problem.
Decelerate stop needs the fan in accordance with the change rate of the VFD frequency deceleration, general it requires long deceleration time, if you need a short time stop you need to consider install an additional brake unit + braking resistor, it's equivalent to energy consumption brake.

If there is no special requirements for the fan in stop mode, you can control the variable frequency drive by the PLC directly, and handle the the feedback current by DC bus.