Control of Modular Multilevel Converters Using an Overlapping Multihexagon Space Vector Modulation Scheme

Abstract

Adapting the conventional Space Vector modulation (SVM) scheme for modular multilevel cascaded converters is complicated as the number of switching vectors increases with the number of voltage levels. This paper introduces a novel SVM scheme that can be applied for the control of modular multilevel cascade converters (MMCC) with any number of levels. Instead of extending a single hexagon to the regions corresponding to the number of levels, the proposed method treats the three-phase MMCC as multiple inverters with a phase limb being a chain of basic three level H-bridge, five-level flying capacitor, or neutral point clamped inverters. Basic two or three level hexagons can be applied to determine the switch states and duty cycles separately within one tier of the converter and many such hexagons can be overlapped, with phase shift relative to each other, for the control of a complete MMCC. This approach simplifies the modulation algorithm and brings flexibility in shaping the output voltage waveforms for different applications. Simulation results confirm the good waveform performance of this scheme. An experimental 5-level MMCC, with a total of six H-bridges as the basic modules, is presented to validate the advantageous features of the method.

Inter-cluster voltage balancing control of a delta connected modular multilevel cascaded converter under unbalanced grid voltage

“…The maximum current flowing in the converter: this is the sum of all the current components as expressed in (18). Only the proposed method operates within the rated current of the converter while the others have higher current flowing in the converter.…”

“…A detailed power flow analysis of delta-connected MMCC operating under unbalanced voltage condition is carried out, and the influence of an unbalanced voltage level on the voltage and current ratings of this configuration is investigated. The MMCC sub-module considered in this paper is the 3level H-bridge (3 L-HB), though the scheme presented can also be applied to a 5-level flying capacitor H-bridge (5 L-FC) [16,18]. Digital simulation test results are presented to validate the proposed method.…”

Minimization of total harmonic distortion and enhancing voltage level for hybrid multilevel converter with different sources

“…8,9 In high-and medium-power applications, four leading MLCs were used, such as a flying capacitor (FC), neutral-point-clamped (NPC), modular MLCs, and cascaded H-bridge (CHB). 10 These multilevel topologies are characterized by enhancing output waveforms, in terms of harmonic content and managing high voltages while utilizing low voltage power electronic components. 11 Papastergiou et al 12 had reported on utilization of a three-level NPC converter for medium applications to extend the voltage levels.…”

“…The MLCs general structure, synthesizes a sinusoidal voltage (usually derived from capacitor voltage sources) from several voltages 8,9 . In high‐ and medium‐power applications, four leading MLCs were used, such as a flying capacitor (FC), neutral‐point‐clamped (NPC), modular MLCs, and cascaded H‐bridge (CHB) 10 . These multilevel topologies are characterized by enhancing output waveforms, in terms of harmonic content and managing high voltages while utilizing low voltage power electronic components 11 …”

Carrier-based sinusoidal pulse-width modulation techniques for flying capacitor modular multi-level cascaded converter

“…However, because of its computational complexity, SHE is not applicable for MMCC-based STATCOM and machine drives, having less numbers of voltage levels, but requiring fast dynamic control. Another widely used modulation technique is the multilevel space vector modulation, this provides extra utilization of the module DC capacitor voltages but poses a complicated modulation algorithm when applied to MMCC [19,20,21].…”