Parallel control for hybrid propulsion of multifunction ships

Multifunction ships, naval vessels in particular, need to reduce fuel consumption while maintaining manoeuvrability. Hybrid propulsion that runs a main diesel engine and electric drive in parallel can achieve this. However, a parallel control strategy needs to be developed. In this paper, we use a simulation model of a hybrid propulsion system to investigate two parallel control strategies for diesel mechanical and electrical propulsion on multifunction ships. For the case study frigate, parallel control can increase the ship top speed with 3 kts when using two 4 MW electric drives and two 10 MW main diesel engines, compared with the same baseline hybrid propulsion without parallel control. The diesel engine speed control with electric drive torque control strategy increases ship acceleration rate with 17% and reduces average engine thermal loading with 150 K. Moreover, the electric drive speed control with diesel engine torque control strategy can improve acceleration rate by 40%, while eliminating thermal loading fluctuation due to heavy seas, and also reducing engine average thermal loading with 150 K. Future combination of the proposed electric drive speed control strategy with an adaptive pitch control and optimal power split strategy can potentially further increase hybrid propulsion plant performance.