Distributed Modulation and Control of Modular Multilevel Converter for HVDC application
Author
Huang, Shaojun
Term
4. term
Education
Publication year
2013
Pages
97
Abstract
Modulær multilevel‑konverter (MMC) er blevet populær til applikationer med høj effekt og højspænding, som f.eks. højspændings‑jævnstrøm (HVDC), fordi den er opbygget af mange ens delmoduler, der kan kombineres efter behov. Men styring af en virkelig MMC med mange delmoduler er vanskelig. Denne afhandling undersøger en distribueret styringsarkitektur, der bevarer modulariteten ved at give hvert delmodul en lokal styring og koordinere dem over et kommunikationsnetværk. Først vurderes de kommunikationsteknologier, der er nødvendige for distribueret styring. To realtidsprotokoller—EtherCAT og SPI—bliver sammenlignet med hensyn til hastighed, netværkstopologi, forbindelsesmuligheder, synkroniseringsnøjagtighed og omkostninger. Et laboratorieprototype baseret på en SPI‑løsning er bygget og testet med succes. Dernæst behandles multiniveaumodulation med fokus på faseforskudt pulsbreddemodulation (PS‑PWM), som forskyder koblingsfaserne mellem delmoduler. Uniform PS‑PWM og resamplet uniform PS‑PWM sammenlignes. Afhandlingen foreslår en ny måde at implementere den resamplings‑teknik, som er central for den resamplede metode, og denne løsning bliver verificeret med simulationer og eksperimenter. Den distribuerede styring analyseres og modelleres i frekvensdomænet (altså hvordan systemet opfører sig ved forskellige frekvenser). Regulatorer designes med analytiske metoder og Matlab‑værktøjer. Systemets følsomhed over for praktiske forhold—modulationsvalg (faseforskydning), kommunikationsforsinkelse, forskelle i individuelle bærefrekvenser (koblingsfrekvenser) og samplefrekvenser—undersøges via simulationer i Matlab/Simulink og PLECS. Til sidst præsenteres hardware- og softwaredesignet for prototypen, og de eksperimentelle resultater dokumenteres.
Modular Multilevel Converters (MMCs) are increasingly used for high‑power, high‑voltage applications such as high‑voltage direct current (HVDC) transmission because they are built from many identical submodules that can be combined to meet different requirements. However, operating a real MMC with a large number of submodules is challenging. This thesis investigates a distributed control architecture that preserves modularity by giving each submodule a local controller and coordinating them over a communication network. We first evaluate the communication technologies needed for distributed control. Two real‑time protocols—EtherCAT and SPI—are compared in terms of speed, network topology, connection capability, synchronization accuracy, and cost. A laboratory prototype using an SPI solution was built and successfully tested. We then study multilevel modulation, focusing on phase‑shifted pulse‑width modulation (PS‑PWM), which shifts the switching phases across submodules. Uniform PS‑PWM and resampled uniform PS‑PWM are compared. The thesis proposes a new way to implement the resampling step that is central to the resampled method and validates it through simulations and experiments. The distributed control system is analyzed and modeled in the frequency domain (i.e., how the system behaves across different frequencies). Controllers are designed using analytical methods and Matlab tools. We assess the system’s sensitivity to practical non‑idealities—including the modulation method (phase shifts), communication delays, differences in individual carrier (switching) frequencies, and sampling frequencies—using simulations in Matlab/Simulink and PLECS. Finally, the hardware and software design of the prototype are presented, and the experimental results are documented.
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