Grid Fault Responses of Voltage-Source Converters in Wind Turbine Applications
Author
Taul, Mads Graungaard
Term
4. term
Education
Publication year
2019
Pages
110
Abstract
Når en større del af elproduktionen sker via effektelektroniske konvertere, opstår bekymringer om elnettets stabilitet og forsyningssikkerhed. For at undgå netkollaps ved fejl kræves såkaldt fault ride-through – evnen til at forblive tilsluttet under kortvarige netforstyrrelser – så mange decentrale produktionsanlæg ikke kobler fra samtidig. Interessen for at styre nettilsluttede konvertere, så de opfører sig som synkrongeneratorer (netdannende styring), er stigende, men der er begrænset viden om, hvordan denne styring opfører sig under netfejl. Dette projekt udvikler en avanceret strømstyret regulator til en nettilsluttet konverter og sammenligner den med en spændingsstyret regulator under både symmetriske (balancerede) og asymmetriske (ubalancerede) netfejl. Resultaterne viser, at en spændingsstyret, netdannende struktur, der efterligner centrale egenskaber ved en traditionel synkronmaskine, giver iboende netsupport og derfor kan være fordelagtig i forhold til en konventionel strømstyret, netfølgende strategi. Under netfejl gør selve princippet bag netdannende styring dog påkrævet strømbegrænsning vanskelig. Projektet beskriver fordele og ulemper ved spændings- versus strømstyring og foreslår en forbedret netdannende regulator, som bevarer fordelene ved spændingsstyring og samtidig muliggør nødvendig strømbegrænsning, så løsningen kan anvendes til fremtidens nettilsluttede konvertere.
As more electricity is produced through power-electronic converters, concerns arise about the stability and security of supply of future power systems. To prevent a system collapse during faults, generators are required to have fault ride-through—the ability to stay connected through short disturbances—so that many distributed units do not disconnect at once. There is growing interest in controlling grid-connected converters to behave like synchronous generators (grid-forming control), but there is limited knowledge about how such control performs during grid faults. This project designs a state-of-the-art current-mode controller for a grid-connected converter and compares it with a voltage-mode controller under both symmetrical (balanced) and asymmetrical (unbalanced) grid faults. The results show that a voltage-mode, grid-forming structure that emulates key aspects of a conventional synchronous machine provides inherent grid support and can be advantageous compared with a conventional current-controlled, grid-following strategy. However, during grid faults, the basic principle of grid-forming control makes the required current limitation difficult to enforce. The project outlines the advantages and disadvantages of voltage- versus current-mode control and proposes an enhanced grid-forming controller that preserves the benefits of voltage-mode control while enabling the necessary current limiting, making this approach practical for future grid-connected converters.
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