Use of active rectifiers with inductive motor drives

It is the case with servo drives that rapid and frequent torque changes in both magnitude and sign are required. If an induction servo motor is fed via a three phase inverter there is an inevitable associated change in the size or direction of power flow across the inverter. A solution to this problem is to feed the DC link from the three phase supply with an active rectifier. This system is symmetrical about the DC link capacitor and this feature allows controlled bidirectional power flow between supply and machine. It can also be shown that there is the considerable advantage that the supply connected convertor will draw or supply sinusoidal three phase currents at unity power factor. The authors describe the action and operation of the active rectifier