Control study of energy storage for all electric ship under extreme conditions

Abstract

Increasing fuel costs and environmental concerns are driving the trend towards more or all electric ships. However, replacing existing diesel engine driven on-board generators with cleaner sources of energy is easier said than done. One major impediment to this structural overhaul is the response of the system under fault conditions and dynamic loading. Unlike land based systems, isolated marine systems have very less inertia and this manifests itself in severe fluctuations in voltage and frequency under harsh conditions. Frequency fluctuation in an AC system occurs due to imbalance in the energy generated and consumed. Li traditional rotating machine driven AC systems, the kinetic energy stored in the rotating elements helps tide over these frequency fluctuations. Higher penetration of energy storage elements will seriously diminish the rotational inertia of the system and also affect its robustness under faults. Voltage control on the other hand is more to do with the relation between reactive power and system voltage. The system has to constantly track the reactive power demand which becomes difficult in the case of operations like dynamic positioning wherein the propellers are constantly switched on and off to position the ships on moving waters. All said and done, the allure in case of energy storage devices in ships lies in the far quicker dynamic response of these systems. It is this feature that has been leveraged in this project. It is aimed as part of this project to create a model of a ship-board power system on which different energy storage devices can be tested. The choice of the energy storage to be incorporated takes into account factors like cost, space, availability etc. Therefore the energy storage has been modeled as a DC voltage source and emphasis has been laid on interfacing this system with existing grid using power electronic converters and controls. Having said that, most of the existing energy storage technologies have been studied in detail and based on that, battery, Supercapacitor and flywheel technologies have been chosen as most suited for this application.