Using an AFD's Inverter to Improve Line-Connected Induction Motor Power Factor within Integrated Control Gear

Abstract

Modern medium voltage motor controls use adjustable frequency drives to sequentially line-synchronize multiple induction motors to the main bus voltage amplitude and phase angle before bumpless transferring them with a bypassing contactor. These switchgear arrangements can include many vacuum contactors that are multiplexed between the main bus, induction motors, and AFD. The authors present a novel approach of using the AFD's back-end inverter and its line-synchronization smoothing reactor for reactive power compensation once all motors operating on the main bus voltage direct. By improving the main bus power factor of line connected induction motors the input current draw will be lowered making the system more Green. This paper will show simulated results of how this approach is implemented.