The need for transmitting power over long distances has led to the search for the most efficient transmission solution; given the results achieved over the last fifty years in the field of research on the AC/DC converters, it has been often opted for the direct current power transmission. This phenomenon is expected to grow: there are projects of real meshed direct current grids, the so called multi-terminal DC grids. In this thesis the frequency regulation issue, for alternated current isolated grids, which are connected through a multi-terminal direct current grid, has been studied. With the integration of renewable sources, the power system has lost part of its robustness in terms of ability to react to power imbalances, so the study of the frequency regulation is essential to ensure a high level of network reliability. In the first part of the thesis two methods for the frequency regulation of an undefined number of isolated AC grids, connected through an MTDC grid, have been presented, together with a control strategy which aims to include the wind turbines in the primary frequency regulation phenomenon. In the second part, different kinds of stability analysis have been carried out on the system embedded with the most reliable control scheme, among the two previously introduced. The block scheme describing the dynamics of the controlled system has been reconstructed and adapted to simulate the evolution of such a system following several different cases of load unbalances, including two different ways to operate the load shedding.
La necessità di trasmettere potenza per lunghe distanze ha portato alla ricerca della soluzione più efficiente per la trasmissione; visti i risultati ottenuti negli ultimi cinquant’anni nell’ambito di ricerca sui convertitori AC/DC, spesso si è optato per la trasmissione di potenza in corrente continua. Questo fenomeno è destinato a crescere: esistono progetti di vere e proprie reti magliate in corrente continua, le cosiddette multi-terminal DC grids. In questa tesi si è analizzata la regolazione di frequenza di reti isolate in corrente alternata, collegate tra loro per mezzo di una rete magliata in corrente continua. Con l’integrazione delle fonti rinnovabili il sistema elettrico ha perso di robustezza, in termini di capacità di rispondere agli squilibri di potenza, per questo lo studio della regolazione di frequenza è fondamentale per garantire un alto livello di affidabilità della rete. Nella prima parte della tesi sono stati presentati due metodi per la regolazione di frequenza di reti isolate, connesse da una MTDC grid, ed un sistema per includere le turbine eoliche nella partecipazione alla regolazione primaria. Nella seconda parte, il metodo ritenuto più affidabile, tra i due presentati, è stato analizzato in dettaglio dal punto di vista della stabilità; lo schema a blocchi rappresentante la dinamica del sistema controllato è stato ricostruito e riadattato per poi simularne la risposta in seguito a diversi casi di sbilanciamento dei carichi, includendo due diverse tipologie di load shedding.
Frequency regulation. Primary and secondary frequency regulations of isolated AC grids connected through an MTDC grid
GARZELLI, LORENZO
2016/2017
Abstract
The need for transmitting power over long distances has led to the search for the most efficient transmission solution; given the results achieved over the last fifty years in the field of research on the AC/DC converters, it has been often opted for the direct current power transmission. This phenomenon is expected to grow: there are projects of real meshed direct current grids, the so called multi-terminal DC grids. In this thesis the frequency regulation issue, for alternated current isolated grids, which are connected through a multi-terminal direct current grid, has been studied. With the integration of renewable sources, the power system has lost part of its robustness in terms of ability to react to power imbalances, so the study of the frequency regulation is essential to ensure a high level of network reliability. In the first part of the thesis two methods for the frequency regulation of an undefined number of isolated AC grids, connected through an MTDC grid, have been presented, together with a control strategy which aims to include the wind turbines in the primary frequency regulation phenomenon. In the second part, different kinds of stability analysis have been carried out on the system embedded with the most reliable control scheme, among the two previously introduced. The block scheme describing the dynamics of the controlled system has been reconstructed and adapted to simulate the evolution of such a system following several different cases of load unbalances, including two different ways to operate the load shedding.| File | Dimensione | Formato | |
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2017_12_Garzelli.pdf
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Descrizione: Testo della tesi
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https://hdl.handle.net/10589/137816