Hierarchical control strategies for Parallel connected Inverters in AC Microgrids: Hierarchical control strategies for Parallel connected Inverters in AC Microgrids
Translated title
Hierarchical control strategies for Parallel connected Inverters in AC Microgrids
Author
Karn, Rajiv Kumar
Term
4. term
Education
Publication year
2021
Submitted on
2021-10-01
Pages
94
Abstract
Efterhånden som bekymringen for global opvarmning stiger, kobles der mere sol- og vindkraft på elnettet. Det øger interessen for mikronet, små elsystemer der kombinerer lokal elproduktion med forbrugere/prosumerer og eventuelt energilagring. Mikronet bruger strømomformere kaldet invertere og styres, så de kan køre fleksibelt, også i ø-drift, samtidig med at den ønskede elkvalitet og energileverance opretholdes. Når flere invertere arbejder parallelt, bruges decentrale metoder som droop-kontrol, en teknik til at dele effekt og regulere spænding og frekvens. En hierarkisk struktur med primær, sekundær og tertiær kontrol kan håndtere lastdeling, synkronisering, styring af effektflow og økonomisk optimering. Denne afhandling udvikler sekundære regulatorer til AC-mikronet baseret på droop-kontrol, både i centraliserede og distribuerede udgaver, for at genskabe spændingsniveau og frekvens selv i nærvær af kommunikationsforsinkelser. Derudover dimensioneres parametre for de indre spændings- og strømsløjfer, virtuel impedans og droop-koefficienter. En harmonikdæmpningsmetode anvendes også til at reducere spændingens totale harmoniske forvrængning (THD) for en trefaset, spændingsstyret inverter med en ikke-lineær last. De foreslåede styrestrategier valideres i Matlab/Simulink og på en dSPACE 1006 hardware-in-the-loop-platform.
As concern over global warming grows, more solar and wind power are being connected to the grid. This increases interest in microgrids, small electricity networks that combine local generation with consumers/prosumers and possibly storage. Microgrids rely on power converters called inverters and are controlled to operate flexibly, including islanded operation, while keeping power quality and energy output within targets. When several inverters run in parallel, decentralized methods such as power droop control, a technique for sharing power and regulating voltage and frequency, are commonly used. A hierarchical control structure with primary, secondary, and tertiary levels can handle power sharing, synchronization, power flow management, and economic optimization. This thesis develops secondary controllers for AC microgrids based on droop control, in both centralized and distributed forms, to restore voltage magnitude and frequency to their targets even when communication delays are present. It also designs parameters for the inner voltage and current control loops, virtual impedance, and droop coefficients. In addition, a harmonic suppression method is applied to reduce voltage total harmonic distortion (THD) for a three-phase voltage-controlled inverter supplying a nonlinear load. The proposed control strategies are validated in Matlab/Simulink and on a dSPACE 1006 hardware-in-the-loop platform.
[This summary has been rewritten with the help of AI based on the project's original abstract]
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