MPC and Energy Storage Based Frequency Regulation Strategy for Hybrid Electric Ships

Propulsion system of a hybrid electric ship is powered by the main engine and a motor coupled to the propeller shaft via a gearbox. The motor provides a power boost when the propulsion load is high and extracts excess power working as a generator at low loading conditions. The power boost comes from the auxiliary engine which is used to supply service loads as well. When excess power is taken out from the shaft it is delivered to the ship power system requiring the auxiliary engine to reduce its power. Consequently, auxiliary engine experiences frequent changes resulting in frequency sags or swells. In extreme conditions these could result in blackouts. In addition, changes in service loads could also lead to frequency deviations causing serious power quality issues. This paper proposes a novel model predictive control (MPC) based strategy to address this issue and thereby improve the power quality. The proposed strategy uses a battery energy storage system to absorb load changes and regulate the frequency of the ship power system. The same approach is tested with the PI controllers as well for performance comparisons. Simulation results are presented to verify the efficacy of the proposed frequency regulation strategy.