Impact of Inductor Placement on DC Bus Capacitor of Adjustable Speed Drives under Non-Ideal Supply Voltage Conditions

Diode bridge front-end Adjustable Speed Drives (ASDs) generally have an inductor either in the DC side (DC choke) or in the AC side (AC choke). Since both the types of ASDs are commercially widely used, a comparison of their behavior under normal and abnormal grid conditions is of interest. It is identified in this work that there exists a difference in the ripple current through the DC bus capacitor between the two variants. Further, the difference in the ripple current varies depending on the type of the disturbance and its level. As an outcome of the study, it is identified that the stress levels arising in the DC choke variant on the DC bus capacitor are lesser compared to the corresponding AC choke variant under balanced, unbalanced, and distorted grid voltage conditions, for the same value of the equivalent inductance in the AC and DC side. In order to match the stress levels arising in the DC bus capacitor between the ASDs with DC and AC choke, it is found that a 50% higher value of inductance is required in an AC choke variant. The effects are analyzed by simulations and validated using an experimental setup.