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New trends of environmental and economical issues have motivated ship end users to pay more attention in producing affordable power solutions for future vessels. This movement has been recognized by the commercial shipbuilding industry and the U.S. Navy and the aspects of integrated Power System (IPS) are introduced into the planning and design of all-electric vessels to improve system utilization and operation. The IPS consists of an architecture and a set of generators which together supply power to ship service loads as well as electric propulsion systems. However, for reliable and efficient operations, an effective system performance study framework is important and essential. To ensure the operating performance of IPS in all-electric vessels under different navigating situations, a dynamic simulation technique based method is employed in this paper for analyzing voltage variations. The dynamic characteristics of IPS are modeled and simulated by the proposed method. To demonstrate the effectiveness of proposed method, a practical vessel IPS with 6110 kVA of generation capacity and two 2200 kW propulsion motors is selected for computer simulation. Test results have shown that with thorough simulations, the system performance with respect to transient and dynamic voltage qualities can be completely represented by the proposed method, which can assist engineers in determining proper system design or mitigation options.

In recent sea and undersea vehicles, implementation of all-electric ships (e-ships) technologies that employ various types of semiconductor switching devices based power conversion modules has brought revolution. These power converters that are nonlinear loads can produce non-sinusoidal distorted currents and these currents are then delivered and broadcasted through the power network and thus bus voltages are distorted. This effect can be more obvious while large loads fed and controlled through power conversion modules, such as electric propulsion system, operate for different purposes of missions. In order to improve the harmonic distortion due to operation of electric propulsion systems, a novel control model for electric propulsion motors is proposed in this paper. The electric motor drivers are controlled through three inverter triggering signals including pulse width modulation (PWM), Quasi-Six Step, and Six-Step for different ship navigation scenarios. Simulation results of application of the proposed model to a practical ship with electric propulsion system are presented. Test results have demonstrated that with the proposed model the harmonic distortions produced by electric propulsion systems under different speed situations can be effectively mitigated and consequently the system supply quality is maintained.