The increasing concern in environmental impacts contributed by the shipping industry leads to a growing interest towards the improvements of ship fuel efficiency. Currently, however, many ships still run with their generators at a set speed, regardless of the power requirement, creating a surplus of wasted energy. For a large cruise ship, for example, up to 6% (or up to 2,000 tons of fuel) of annual savings can be achieved by engine speed optimisation. Thus, variable frequency/speed power generation shows significant potentials in improving fuel economy.
There are several ways of achieving variable speed generator engine operation, and most commonly would be either by DC distribution of main power or by allowing a variable frequency at the main AC system(which in this text, is named as Dynamic AC (D-AC)). However, fuel efficiency will not be maximized if power split between the power sources are not handled properly. Therefore, advanced power management system (PMS) is necessary to exploit the full potential of the onboard power system to achieve significant reduction in fuel consumption or emissions. Fig.1 shows the diagram of the control architecture of shipboard microgrid, which consists of local and centralized controllers and communication systems. The primary controller is responsible for the local voltage control and for ensuring a proper power sharing inside the zone and a stable microgrid operation. The secondary and tertiary controllers support the microgrid operation and can address multiple objectives.
This project will detailed investigate the problems concerning D-AC and DC ship microgrids. Architecture of the D-AC and DC ship microgrids will be researched and designed, especially using zonal electrical distribution (ZED) system, to develop a more flexible and reliable topology structure. Energy storage system (ESS) will be integrated in the D-AC and DC ship microgrids with advanced control method to achieve high inertia support to the system. In addition, a hierarchical PMS control architecture for ZED-based D-AC and DC shipboard power systems will be proposed to coordinate synchronous generators, ESS and propulsion loads. In the architecture, specific fuel oil consumption (SFOC) based droop mechanism of paralleled synchronous generators will be applied to achieve optimal load sharing considering the load variation. Distributed high control level will be developed to achieve global optimization objectives. In addition, the hierarchical control structure will deal with optimal power management of D-AC and DC shipboard microgrids to reduce propulsion and energy consumption. Finally, text on the proposed control strategies will be carried out by simulation and full-scale experiments.
Funding: CSC (China Scholarship Council).