Active Filters for Standard-Compliant Power Quality in Electrical Networks

Abstract

The article is devoted to the analysis of three circuits of modular multilevel converters (MMCS) with cascade connection of single-phase bridge and half-bridge voltage converters, each of which operates in pulse width modulation (PWM) mode. The main feature of active filters based on MMS is the possibility of selective high-speed harmonic filtering in on–line mode: AF allows the suppression of any given set of harmonics, including the negative harmonic of the fundamental frequency (reverse sequence), with a given degree of suppression - to zero or a normalized value - by an appropriate task in the control program. For the practical implementation of MMS in solving problems of normalization of electricity quality indicators, the so-called DSB control algorithm of MMS was developed, based on the traditional "classical" theory of automatic control and the theory of three-phase circuits. A comparative assessment of the use of various MMC schemes for symmetry and reactive power compensation has been carried out. It is shown that the problem of voltage symmetry using MMS is a special one, requiring the use of special algorithms to solve it, ensuring the reactive nature of branches of MMS circuits.