Control and operation of a ship AC/DC microgrid under transient propulsion and manoeuvring load conditions

Moving towards more electric ships with sustainable designs can help in reducing the carbon footprint of the global transportation systems. Ship networks can be based on AC/DC microgrids with resilient structures to accommodate different types of power-generation and energy storage systems for supporting the dynamic loads of the vessel's propulsion and bow-thruster units. This paper presents a shipboard AC/DC microgrid with a supercapacitor (SC) system to support the ship's power system and to enhance its operational reliability under severe/ transient loading scenarios, mainly arising from abrupt changes in the propulsion and bow-thruster power. A control system with SC voltage re-balancing mechanism is proposed for stabilizing the DC-bus voltage via bidirectionally power-controlled DC-DC converters utilizing the non-linear hyperbolic functions. The mechanism concurrently generates steady, slow-changing diesel-driven power through the microgrid voltage source converters to re-balance the SC voltage. The power system, including the diesel-generators, the microgrid components and the propulsion/thruster units, has been simulated in detail using the physical modelling-tools in the Matlab-Simulink (R) software, and run under harsh loading scenarios. The results demonstrated the effectiveness of the proposed control system with the microgrid structure and compared favourably with those obtained using other methods reported in the literature.