The 90% of the world global trade is based on maritime transportation. Therefore, vessel’s sector has a remarkable impact in terms of global economy and, especially, in green-house gas emissions. As a consequence, the international maritime community is driving a transition towards new and more efficient maritime system prototype. One of the proposed strategies to increase the efficiency of the vessels is to replace the classic AC marine electric power system (EPS) with the new generation DC shipboard microgrid. The aim of this study is to analyse and implement a speed control strategy for the Diesel Prime Movers that characterize the generation system on-board the marine microgrid. The main idea of this study is based on the fact that the diesel generator not only has an optimal operation point, but it is also characterized by an optimal mechanical speed for each operation point, which implies a further reduction in fuel consumption for each generator present into the grid. The DC technology enables the Diesel Generator Sets, which represent the electric power generation system on-board the ship, to work at their optimal operation speed due to the lack of synchronization between generation and load sides. In this study, a strategy based on variable speed control is implemented into a marine DC microgrid of a specific marine class ship, the Bulk Carrier Vessels. A reference speed controller is implemented into the Governor of the diesel generator sets in order to keep the mechanical speed close to the optimal reference value. The potential of this strategy was evaluated analysing a typical sea-voyage of a Bulk Carrier Ship, from the Port of Taipei to Hong-Kong. Only electric propulsion system was taken into account as electric user, representing the about the 90% of the electrical power consumption on-board the marine vessel. Average load profile for five different operation conditions was obtained according to the Marine standard for propulsion speed. In order to evaluate the effect of the proposed methodology in terms of generator efficiency, the complete marine DC microgrid of the Bulk Carrier Vessel was modelled into Matlab/Simulink software and several cases have been proposed in order to investigate the potential of the variable speed strategy. Further, an energy storage system based on battery technology was integrated into the system, being one of the current directions for a green-ship concept and able to make generation system work close to the optimal operation point, especially during the low loading condition in harbouring operation. To evaluate the effectiveness of the applied strategy in terms of fuel efficiency, results have been compared through the calculation of the Specific Fuel Consumption (SFC) index, being directly proportional to the CO2 emissions and to the Energy Efficiency Design Index (EEDI), which represents a standard introduced by the international maritime organization (IMO) in order to move towards more fuel-efficient ships. Unfortunately, the available materials on this new trend of DC marine system technology is still inadequate and fragmented, therefore, several assumptions and simplifications have been supposed in order to conduct the study, being also difficult to retrieve technical information from the specialized companies.
Il 90% del commercio mondiale avviene attraverso mezzi di trasporto marittimi. Pertanto, il settore navale ha un notevole impatto in termini di economia globale e, soprattutto, in termini di emissioni di gas serra. Di conseguenza, la comunità marittima internazionale ha avviato una transizione verso un nuovo e più efficiente prototipo di imbarcazione navale. Una delle strategie proposte per aumentare l'efficienza a bordo di una nave è quella di sostituire il sistema elettrico di bordo in AC con il concetto di DC Microgrid di nuova generazione. Lo scopo di questo studio è quello di analizzare e attuare una strategia di controllo della velocità per i Generatori Diesel (Prime Movers) che caratterizzano il sistema di generazione a bordo delle Microgrid marine. Il concetto fondamentale dal quale questo studio prende forma è che il generatore diesel non solo è descritto da un punto di funzionamento ottimale in termini di potenza generata, ma è anche caratterizzato da una velocità meccanica ottimale per ogni punto di funzionamento, il che implica un’ulteriore riduzione del consumo di carburante per ogni generatore presente a bordo. La tecnologia DC consente ai Generatori Diesel, i quali rappresentano il sistema di generazione di energia elettrica a bordo della nave, di lavorare alla loro velocità ottimale, data la mancanza di sincronizzazione tra il sistema di generazione e i diversi carichi presenti a bordo. In questo studio, una strategia di controllo della velocità è implementata in una DC Microgrid a bordo di una specifica classe navale, le navi portarinfuse. Il riferimento di velocità ottimale è definito da un regolatore implementato nel governor dei generatori diesel al fine di mantenere la velocità meccanica vicina al valore di riferimento ottimale. Il potenziale di questa strategia è stato valutato analizzando un tipico viaggio per mare di una nave portarinfuse, dal porto di Taipei a Hong-Kong. Solo il sistema di propulsione elettrica è stato preso in considerazione come utente elettrico, rappresentando circa il 90% del consumo di energia elettrica a bordo della nave. Il profilo di carico medio per cinque diverse condizioni operative è stato ottenuto in accordo alla potenza elettrica richiesta per mantenere la nave ad una determinata velocità di navigazione. Al fine di valutare l'effetto della metodologia proposta in termini di efficienza del sistema di generazione, il sistema elettrico della nave Portarinfuse è stato modellato tramite l’utilizzo del software Matlab / Simulink, dove sono stati proposti diversi casi per indagare il potenziale della strategia a velocità variabile. Inoltre, un sistema di accumulo di energia basato su batterie agli ioni di litio è stato integrato nel sistema, in modo da permettere al sistema di generazione di lavorare vicino al punto di funzionamento ottimale, specialmente durante le operazioni in area portuale. L'efficacia della strategia è stata valutata in termini Specific Fuel Consumption (SFC), indice di efficienza direttamente proporzionale alle emissioni di CO2, introdotto dalla comunità marittima internazionale. Diverse ipotesi e semplificazioni sono state assunte per condurre lo studio data la difficoltà nel reperire informazioni tecniche per quanto riguarda la fase di modellizzazione dei generatori diesel.
Diesel gen-sets optimization in electric powered ship for efficiency improvement
POMETTI, PASQUALE
2017/2018
Abstract
The 90% of the world global trade is based on maritime transportation. Therefore, vessel’s sector has a remarkable impact in terms of global economy and, especially, in green-house gas emissions. As a consequence, the international maritime community is driving a transition towards new and more efficient maritime system prototype. One of the proposed strategies to increase the efficiency of the vessels is to replace the classic AC marine electric power system (EPS) with the new generation DC shipboard microgrid. The aim of this study is to analyse and implement a speed control strategy for the Diesel Prime Movers that characterize the generation system on-board the marine microgrid. The main idea of this study is based on the fact that the diesel generator not only has an optimal operation point, but it is also characterized by an optimal mechanical speed for each operation point, which implies a further reduction in fuel consumption for each generator present into the grid. The DC technology enables the Diesel Generator Sets, which represent the electric power generation system on-board the ship, to work at their optimal operation speed due to the lack of synchronization between generation and load sides. In this study, a strategy based on variable speed control is implemented into a marine DC microgrid of a specific marine class ship, the Bulk Carrier Vessels. A reference speed controller is implemented into the Governor of the diesel generator sets in order to keep the mechanical speed close to the optimal reference value. The potential of this strategy was evaluated analysing a typical sea-voyage of a Bulk Carrier Ship, from the Port of Taipei to Hong-Kong. Only electric propulsion system was taken into account as electric user, representing the about the 90% of the electrical power consumption on-board the marine vessel. Average load profile for five different operation conditions was obtained according to the Marine standard for propulsion speed. In order to evaluate the effect of the proposed methodology in terms of generator efficiency, the complete marine DC microgrid of the Bulk Carrier Vessel was modelled into Matlab/Simulink software and several cases have been proposed in order to investigate the potential of the variable speed strategy. Further, an energy storage system based on battery technology was integrated into the system, being one of the current directions for a green-ship concept and able to make generation system work close to the optimal operation point, especially during the low loading condition in harbouring operation. To evaluate the effectiveness of the applied strategy in terms of fuel efficiency, results have been compared through the calculation of the Specific Fuel Consumption (SFC) index, being directly proportional to the CO2 emissions and to the Energy Efficiency Design Index (EEDI), which represents a standard introduced by the international maritime organization (IMO) in order to move towards more fuel-efficient ships. Unfortunately, the available materials on this new trend of DC marine system technology is still inadequate and fragmented, therefore, several assumptions and simplifications have been supposed in order to conduct the study, being also difficult to retrieve technical information from the specialized companies.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/141847