DC adjustable speed motor drives

typically use current source power converters and have a series connected DC reactor in the intermediate circuit between the rectifier and the inverter. The phase commutation of the SCR rectifiers in the input of the drive generates network harmonic distortion, the intensity of which is a function of the impedance of the upstream network. Line reactors add their impedance to the impedance of the electrical system which results in lower electrical system harmonic distortion.

In the case of AC (variable frequency) motor drives

a capacitor is connected (in parallel with the DC bus) in the intermediate circuit between the rectifiers and the inverter. The presence of this DC bus capacitor causes intermittent current flow form the power source to the rectifiers. The addition of a series connected line reactor reduces the discontinuity of the input current flow in the upstream network and results in less generation of harmonic distortion. Furthermore, the line reactor provides and additional benefit to the drive system through a considerable reduction of the inrush current in the intermediate DC bus capacitor due to the reactor's impedance.