AC Line reactor VS DC choke in variable frequency drive

AC line reactors reduce current harmonics on AC line which is caused by rectifier, while DC choke deal with DC bus current.

Use a line reactor or use a DC choke will depended on the application of the variable frequency drives relative to the utility power system to prevent excess current that may possibly damage VFD drives during events such as line disturbances or certain types of ground faults. AC Drives should have a minimum amount of impedance in front of them but an evaluation of the application and where it is located is just as important. Impedance comes from the transformer(s) and line side power cables. Some cases a line reactor is recommended in front of the variable frequency drive when some application has switching power factor correction capacitors. The AC drive maybe installed in an area that has a large potential lighting strike in the area. Maybe there are large power interruptions or voltage dips that could potential damage the VFD drive that may need to be evaluated. In addition the primary utility transformer may be too large in comparison to the AC drive thus an impedance matching evaluation may be calculated relative to the frame size of the VFD. Ask for the recommendation of installation by the VFD manufacturer. They will advise how the proceed and what and when to provide a line reactor relative to the application mounted in a motor control center or a wall mount design.

My personal preference is for an AC line reactor simply because it does a better job of protecting the variable frequency drive from the line and the line from the drive. I've always viewed a DC bus reactor on a PWM drive as a cheap attempt at filtering to save space and money over the better protection afforded by a line reactor.