I. Introduction
Electricity quality control issues are becoming increasingly important with the introduction of digital technologies into energy systems and the intellectualization of energy networks. Digitalization and widespread automation increase the use of non-linear semiconductor elements in power supply systems, resulting in distortion of electricity parameters. Non-linear load includes: power electronic equipment, AC frequency drives, DC drives, rectifiers, uninterruptible power supplies, elements containing diode bridges, lighting (fluorescent, gas-discharge LED) saturated electromagnetic devices (transformers, motors) etc.