Impact of online PPL accommodation on quality of power in an AES’ MVDC distribution system

Quality of electrical power onboard ships is an important area, since there are stringent power quality standards set by the classification societies. In an all-electric ship (AES) with alternating current distribution, the power quality issues become more serious similar to those in inland power systems. Recent trend in modern AES is to utilize the medium voltage direct current (MVDC) distribution system. The presence of power electronic converters in the DC distribution system, and their high frequency switching creates voltage ripple and noise at the direct current (DC) bus. There evolves the importance in the effective analysis on MVDC bus voltage quality, since quality of power and its continuity is utmost important onboard ships. This paper focuses on the simulation studies of a 6 kV MVDC distribution system onboard ship with propulsion motor, pulsed power loads and some service loads operated. Each load is energized in a particular sequence to identify their impact on the DC bus. Quality of power at the DC bus is analysed as per the standards set by the IEEE 1709. Also the impact of online accommodation of pulsed power load (PPL) on DC bus voltage and its stability is examined. Simulation results and their analysis can be useful for the design of pulsed load profile in certain situations and for the design of proper filters and sufficient energy storages in some other cases. With the pulsed power load deployment in online mode, the DC bus voltage crosses the permitted tolerance which comes around -13.98%, and the angular velocities of generators have reduced by 3 to 4%. Results show that, with the pulsed power load operation, the quality and stability of the DC Bus voltage is deteriorated.