DC shipboard microgrids are currently of interest since different benefits can be obtained from their adoption. Nevertheless, one of the most important challenges present in this type of systems is due to the presence of sudden load events that demand significant amounts of power within a short period of time, leading to large deviations in the voltage. To cope with this problem the usage of storage systems has been identified as a possible solution. This thesis proposes a control strategy, based on the participation of a battery energy storage system (BESS), that aims to reduce the voltage deviations at the main DC busbar. The proposed control strategy is based in the classic master-slave architecture but with some modifications in order to allow the active participation of the BESS. Here, the master role is shared between the generator and the BESS. The former takes the role of master (i.e., it is in charge of the DC voltage regulation) during the normal operation of the system, while during sudden changes of load it becomes a slave and the BESS takes the role of master. To carry out the proposed strategy, only few signals are exchanged between converters (operation signal of the battery and the active power measured by each converter), while the other required signals are local measurements, i.e., measures taken at the input or output of each device, increasing the general reliability of the control strategy. In addition, this allows the strategy to be flexible, then it can be adapted to the usual schemes used for on-board microgrids (distributed or centralized). Moreover, in the proposed control, when the battery enters in operation, the demanded power could be high but during small periods of time, this avoids the deep discharge of this device, thus its life-time is prolonged. Furthermore, the same fact assures the availability of the storage system during the islanded operation. The obtained results show that the proposed control effectively mitigates the voltage deviations at the main DC busbar, either for sudden long-term or short-term load changes, allowing a secure operation and increasing the general stability of the system.
Le microreti in continua a bordo nave sono attualmente interessanti poiché diversi vantaggi possono essere ottenuti dalla loro adozione. Tuttavia, una delle sfide più importanti presenti in questo tipo di sistemi è dovuta alla presenza di grandi carichi dinamici che richiedono quantità significative di potenza in un breve periodo di tempo, portando a grandi deviazioni nella tensione. Per risolvere questo problema l’utilizzo dei sistemi di stoccaggio di energia è stato identificato come una possibile soluzione promettente. Questa tesi propone una strategia di controllo basata sulla partecipazione di un sistema di accumulo di energia a batteria (BESS) per redurre la deviazione della tensione sul bus principale in continua. La strategia di controllo proposta si basa sulla classica architettura master-slave ma con alcune modifiche per consentire la partecipazione attiva del BESS. Nella strategia proposta, il ruolo principale è condiviso tra il generatore e il BESS. Il primo assume il ruolo del master (cioè, è responsabile della regolazione della tensione DC) durante il normale funzionamento del sistema, mentre durante improvvisi cambi di carico diventa uno slave e il BESS assume il ruolo del master. Per realizzare la strategia proposta, solo pochi segnali vengono scambiati tra i convertitori (segnale di funzionamento della batteria e potenza attiva misurata da ciascun convertitore), mentre gli altri segnali necessari sono misure locali (misure prese all’ingresso o all’uscita di ciascun dispositivo), aumentando, così, l’affidabilità generale della strategia di controllo. Inoltre, ciò consente alla strategia di essere flessibile. Può, quindi, essere adattata ai soliti schemi usati per le microreti (distribuite o centralizzate). Inoltre, nel controllo proposto, quando la batteria entra in esercizio, la potenza richiesta potrebbe essere elevata ma per brevi periodi di tempo evitando la scarica profonda di questo dispositivo e prolungando il suo tempo di vita. In aggiunta, lo stesso fatto assicura la disponibilità del sistema di accumulo durante l’operazione in isola. I risultati ottenuti mostrano che la strategia di controllo proposto attenua efficacemente le deviazioni di tensione sul bus principale DC, in caso di improvvisi cambiamenti di carico permanenti e/o transitori, consentendo un funzionamento sicuro e aumentando la stabilità generale del sistema.
Control of DC shipboard microgrids. Mitigation of voltage deviations due to fast load changes through the utilization of energy storage systems
FERNANDEZ PORRAS, JOSE PABLO
2016/2017
Abstract
DC shipboard microgrids are currently of interest since different benefits can be obtained from their adoption. Nevertheless, one of the most important challenges present in this type of systems is due to the presence of sudden load events that demand significant amounts of power within a short period of time, leading to large deviations in the voltage. To cope with this problem the usage of storage systems has been identified as a possible solution. This thesis proposes a control strategy, based on the participation of a battery energy storage system (BESS), that aims to reduce the voltage deviations at the main DC busbar. The proposed control strategy is based in the classic master-slave architecture but with some modifications in order to allow the active participation of the BESS. Here, the master role is shared between the generator and the BESS. The former takes the role of master (i.e., it is in charge of the DC voltage regulation) during the normal operation of the system, while during sudden changes of load it becomes a slave and the BESS takes the role of master. To carry out the proposed strategy, only few signals are exchanged between converters (operation signal of the battery and the active power measured by each converter), while the other required signals are local measurements, i.e., measures taken at the input or output of each device, increasing the general reliability of the control strategy. In addition, this allows the strategy to be flexible, then it can be adapted to the usual schemes used for on-board microgrids (distributed or centralized). Moreover, in the proposed control, when the battery enters in operation, the demanded power could be high but during small periods of time, this avoids the deep discharge of this device, thus its life-time is prolonged. Furthermore, the same fact assures the availability of the storage system during the islanded operation. The obtained results show that the proposed control effectively mitigates the voltage deviations at the main DC busbar, either for sudden long-term or short-term load changes, allowing a secure operation and increasing the general stability of the system.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/135810