A medium-voltage DC (MVDC) with series active injection for shipboard power system applications

Modern electric ships utilize a medium-voltage zonal dc distribution system to meet the ever increasing power demand while keeping the power density as low as possible. Power electronics building blocks (PEBBs) composed of different DC/AC and DC/DC converters are used to convert the main DC bus voltage to appropriate dc and ac voltage levels suited for the loads in such a system. Due to the fact that most of these power electronic converters present a constant power load (CPL) with negative incremental impedance at the input terminal, the interaction of these converters under different system configurations with the main AC-DC rectifier of the MVDC system might induce voltage oscillations on the main DC-bus. In this paper, a novel method of series active injection on the dc-side is proposed to smooth out disturbances on the main DC-bus. This has resulted in much smoother DC-bus voltage enabling the system to use less amount of passive storage elements on dc-side which is very beneficial to ship´s limited onboard space. The simulation results presented verify the operation and functionality of the proposed system.