AbstractsComputer Science

AbstractModular Multilevel Converter (MMC) features many advantages for high-voltage direct current (HVDC) transmission. Using modulation by phase-shifted triangular carrier, MMC has low switching loss and low harmonic distortion in the high frequency spectrum. While the low frequency distortions, especially the 2nd harmonics, proliferated by single-phase ac power, have to be filtered by large capacitors in the sub-modules. In this thesis, harmonic function analysis is applied to pin-point the source of 2nd harmonic circulating current in MMC. After extending harmonic function analysis, a feed-forward elimination method is proposed by modifying the modulation signal. Analytical insight enables the 2nd harmonic circulating current to be eliminated at the source and, in turn, other low-order harmonic voltages which are proliferated from the 2nd. In order to prevent large fault currents to overcharge the sub-module capacitor and ensure the viability of the feed-forward elimination method, deadbeat control is incorporated in MMC. With deadbeat, MMC becomes a reference current regulator; the ac currents in tracking the current references do not rise to destructively large values during ac faults. Likewise, inherent MMC 3rd harmonic currents on the ac-side cannot flow. This frees MMC from the necessity of having delta or open wye connected transformers. Simulation studies validate the predictions and claims with Simulink of MATLAB.By introducing harmonic function analysis of MMC, this thesis also shows that on the dc side, the equivalent circuit of each phase consists of ideal voltage sources, which suggests that MMC has a future role as Ultra-HVDC for higher voltage dc transmission. Meanwhile, power balance equation inherent in MMC ensures its feasibility for parallel connection to form multi-terminal HVDC networks. Simulation results verify the viability of MMC for the application of Ultra-HVDC and multi-terminal HVDC. Moreover, a mathematical model suitable for load-flow analysis of multi-terminal HVDC networks in steady-state is developed and validated. Performance of MMC back-to-back HVDC under parallel computation condition is evaluated by RT-LAB. RésuméLe convertisseur modulaire à multiple niveau (MMC) dispose de nombreux avantages pour la transmission de courant continu haute tension (CCHT), en anglais High Voltage Direct Current (HVDC). Utilisant la modulation par porteuse triangulaire à changement de phase, le MMC a une perte faible de commutation et distorsion harmonique dans le spectre à haute fréquence. Alors que les distorsions de basse fréquence, en particulier les 2èmes harmoniques, proliféré par une alimentation en courant alternatif monophasé, doivent être filtrées par les gros capaciteurs dans les sous-modules. Dans cette thèse, l'analyse harmonique fonctionnelle est appliquée afin de pointer la source de courant du 2ème harmonique circulant dans le MMC. Après l'extension de l'analyse harmonique fonctionnelle, un procédé d'élimination commande anticipatrice est proposé en modifiant le signal de…