Control of Modular Multilevel Converter(MMC) based HVDC application under unbalanced conditions
Authors
Parikh, Harsh Rajesh ; Sanchez Martin-Loeches, Ruben
Term
4. term
Education
Publication year
2016
Submitted on
2016-05-25
Pages
120
Abstract
Denne afhandling undersøger en ny type effektomformer kaldet MMC, som kan håndtere meget høje spændinger og effekter og anvendes i VSC‑HVDC‑transmissionssystemer. Fordi MMC er en kompleks topologi, fokuserer afhandlingen på en vigtig udfordring: ubalancer i systemet, som opstår internt og under asymmetriske netfejl. Arbejdet forklarer og implementerer sorterings- og selektionsmetoder (varianter NLC, CTB og RSS). Det påvises, at ubalancer medfører ulige energilagring i konverterens arme og faser, og der foreslås energiregulatorer for at udligne energifordelingen. Da HVDC‑forbindelser skal forblive tilsluttet under netfejl, præsenteres og simuleres en strategi for injektion af udgangsstrøm under fejl med henblik på at overholde netkoder. Derudover introduceres en systematisk tilgang til effektiv reduktion af summen af kondensatorspændingsripple i en MMC‑applikation. Endelig er der bygget en lille prototype, og der præsenteres eksperimentelle resultater.
This thesis studies an emerging power‑converter design called MMC, suitable for very high voltages and power, used in VSC‑HVDC transmission systems. Because MMCs are complex, the thesis focuses on a key challenge: electrical unbalance that arises inside the converter and during asymmetrical grid faults. The work explains and implements sorting and selection control methods (variants NLC, CTB, and RSS). It shows that unbalance leads to unequal energy stored in the converter’s arms and phases, and proposes energy controllers to remove this inequality. Since HVDC links must remain connected during grid faults, the thesis presents and simulates an output current injection strategy during faults to comply with grid codes. It also introduces a systematic way to reduce the sum of capacitor voltage ripple in an MMC application. Finally, a small prototype was built and tested, and experimental results are provided.
[This abstract was generated with the help of AI]
Documents