Modeling and Topology Evaluation for Rectifier Circuits in Medium Voltage Direct Current System

Naval ship propulsion design is evolving from the traditional structure with a main engine driving a shaft through a reduction gear to a new architecture that uses electric drives powered from a direct current (DC) power distribution system. The goal of this thesis is to compare different medium voltage rectifier sinter facing an alternating current (AC) generator to a DC bus which can power the ship propulsion system. Power quality and efficiency of the power converters are the parameters used to compare four different rectifier circuit topologies: 2-level converter, 3-level converter, modular multi-level converter, and modular multi-level rectifier. Converter operating principles, design trade-offs, modeling characteristics, performance, and naval shipboard applicability are discussed in detail. Using a power electronics simulation platform, the four power rectifier circuits and their controls are connected between a 6.6kV AC generator and a regulated DC bus that represents the shipboard platform. Inside each rectifier circuit, thermal properties of the chosen semiconductor switching devices and diodes are built in and losses are captured and analyzed in steady state operation. This study shows that the modular multi-level rectifier circuit is the most efficient, easiest to maintain, and the recommended topology for naval shipboard applications.