Non-periodic currents: their properties, identification and compensation fundamentals

Before the area of power electronics was developed, nonperiodic currents occurred in distribution systems, apart from arc furnaces supply, mainly during switching and faults. Now, such currents are produced at normal operation of some power electronics equipment. Power electronics enables very fast control of processes and energy flow. Nonperiodic currents are a by-product of such a fast control. Identification of nonperiodic currents and their compensation is the subject of this paper. The paper discusses the main properties of nonperiodic currents, provides their classification and introduces a concept of coperiodic, noncoperiodic and quasi-periodic currents as well as the concept of interharmonic noise and quasi-harmonics. The paper provides fundamentals of quasi-periodic current compensation and discusses a hybrid control algorithm of a hybrid compensator