An Approach to Modeling and Analysis of Ship Propulsion Electric Drives

Design of high-performance electric propulsion systems requires thorough dynamic analysis of both the electric power and propulsion systems. This paper presents a simple but effective method to model the relevant components in the electric and propulsion plants to facilitate the integration and analysis of the entire system for the purpose of predicting the overall system performance. The objective is to illustrate an approach to integrate the electric and propulsion subsystems in a modeling and simulation environment that can potentially expose alternatives in component design. By way of examples, the paper addresses modeling, analysis, and validation of electric motor propulsion systems as well as hybrid systems that consist of a gas turbine engine and an electric motor driving the same propeller shaft. An instance of the hybrid propulsion systems is the LHD 8 propulsion design discussed in a recent conference publication by the NAVSEA engineering staff. A specific issue in the hybrid propulsion system is the starting of a shaft on electric drive and then clutching in the gas turbine engine. This scenario exists in the system due to differences in operational speed range and performance dynamics of the gas turbine and the electric motor. Using the resulting system model, the examples in the paper will demonstrate the behavior of the subsystems based on this particular scenario. The dynamic models under consideration are representative of the actual systems and are sufficiently robust for use in a preliminary design analysis of electric propulsion drives. An added benefit of the models is the ability to examine different performance aspects of the power distribution system, e.g. sizing of electronic filters in the motor drive, as a function of propeller shaft acceleration. The method presented in this paper is in general applicable to both conventional and hybrid electric propulsion systems. Furthermore, appropriate use of the models and the analysis tool can facilitate integration study as the power system is integrated with the propulsion aspects allowing evaluation of the power plant capability and operational requirements against the ship‟s hull dynamics.