Abstract
In this paper, a triple-layer sequential model predictive control (SMPC) approach without weighting factors is proposed for a three-phase two-leg 7-level T-type nested neutral point clamped (T-NNPC) converter. The main objectives of this paper are to eliminate the selection of weighting factors and enhance the reliability of system in the control process. In the proposed design, three cost functions are formulated in a cascaded way to avoid the weighting factors tuning while not compromising the computational complexity. Furthermore, the three-phase two-leg 7-level T-NNPC converter is investigated to improve the fault-tolerance ability in case of a faulty leg condition. Finally, the effectiveness of the control methodology for the three-phase two-leg 7-level T-NNPC converter is validated by comparative simulation studies.
Highlights
Multilevel voltage source converters (VSCs) are attractive and widely accepted for high-power medium-voltage applications, such as transmission systems, static synchronous compensator and wind turbine applications
The flying capacitor (FC) converter, neutral-point-clamped (NPC) converter, and the cascaded H-bridge (CHB) converter are regarded as the classical multilevel converters and successfully commercialized in manufacturing
The number of FCs increases substantially for FC topology operating at a higher number of voltage levels, which decreases the reliability of the system
Summary
Multilevel voltage source converters (VSCs) are attractive and widely accepted for high-power medium-voltage applications, such as transmission systems, static synchronous compensator and wind turbine applications. New power converter topologies and latest achievements in terms of control have expanded the application of the multilevel converters to renewable energy conversion, machine drives, among others. Compared with conventional two-level converters, the multilevel converters have a better harmonic performance of the output waveforms, higher operating voltages, lower switching loss, and reduced size of output filter elements and interface transformers [1]–[4]. Significant drawbacks of these classical topologies limit their applications for high power density and voltage levels. The number of FCs increases substantially for FC topology operating at a higher number of voltage levels, which decreases the reliability of the system. The using of NPC converter for higher power density system requires a large number of clamping diodes. For the CHB converter, several isolated dc sources generated by the bulky phase-shifting
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