AC–AC Modular Multilevel Converter—Hexverter

Abstract

This article proposes the study, control and analysis of the topology of an AC–AC modular multilevel converter, known in the literature as the Hexverter. The Hexverter is capable of converting the energy between two AC systems with a reduced number of elements, if compared with other modular multilevel topologies, which makes this topology attractive in AC–AC applications. However, there are few studies about the Hexverter in the literature, so this work presents its operation principle, conducts modeling, and proposes a control scheme for the converter’s proper operation, validating the operation and control via hardware-in-the-loop emulation.

Lyapunov control strategy for low-frequency offshore wind power based on hexagonal converters

“…Where: usd+, usq+, usd-, usq-are the positive and negative sequence components of the low-frequency side voltage in the dq coordinate system, respectively; isd+, isq+, isd-, isq-are the positive and negative sequence components of the low-frequency side current in the dq coordinate system, respectively. Due to the fact that there are six controlled variables corresponding to four control variables in equation (11), it is necessary to select the controlled variables according to different grid requirements. The control objectives are as follows: 1) Control Objective 1: Balance grid current The purpose of this control is to balance the three-phase grid currents so that the negative sequence currents are all 0.…”

“…However, their maximum voltage gain is 0.866, and their power rating is relatively low [9].Modular multilevel matrix converter (M3C) overcomes the limitation of maximum voltage gain in traditional MCs, increasing power and voltage levels. However, its internal structure is complex, and control operations are challenging [10][11]. On the other hand, hexagon converter (Hexverter), based on M3C, reduces the number of bridge arms from 9 to 6, thereby reducing operational difficulties and costs.…”