Reactive power compensation through synchronization of networked VFDs

Abstract

Three phase induction machines are widely used in the industry due to their low cost and ease of maintenance, however, their lagging power factor is an inherent disadvantage which is compensated by use of various methods. Variable frequency drives for induction motors offer a mechanism for both power factor correction and efficient control but requires an internal energy buffering for reactive power at line frequency. Our paper introduces a way of synchronizing the operation of multiple induction motors in an organization through networked VFDs driven either through a common DC bus or directly from the AC mains to improve the power factor without the need of energy buffering or use of external capacitor banks. The processed power supplied to the machines through VFDs is phase shifted in voltage to create a time delay in requirement of reactive power allowing the operation of selected induction machines in leading power factor mode. This paper presents the analysis, simulations and experimental validation through results in the lab by implementing two custom 3-phase induction motor drives and their synchronous operation from a common DC bus. The obtained results validate that this approach can be applied to larger networks of induction motors in a larger industrial setup.