A Novel Control Model for Electric Propulsion Systems in All-Electric Ships

Abstract

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.