Reactors for AC drives are available as either AC reactors or DC reactors (DC link chokes). Both serve the same main purpose: to smooth the current flow to the AC drive, and reduce damaging harmonics produced on the power line.
First, let’s look at the AC line reactor. In addition to providing protection from voltage transients created by power factor capacitor switching and lighting surges, the AC reactor also offers a degree of reduction of harmonic distortion the VFD generates back into the line. If we take a typical VFD with no built-in DC reactor and add a 5% AC input reactor, we can bring the THD it produces from roughly 77% down to roughly 35%.