Frequency-Dependent on-Board Impedance Measurements of Ships with AC and DC Grids

This paper presents, for the first-time, measurement results of frequency-dependent impedances of ship electrical systems, obtained during three measurement campaigns. The introduction covers shipboard networks, the trend towards DC networks and explains the measurement procedure. The results from an AC secondary ship grid on an AC-ship, a fixed DC system, and a floating DC system installed on a ferry are presented, compared and discussed. The three shipboard power networks all show resonances in various degrees and different characteristic curves of the magnitudes and phase curves of the impedance. The frequency-dependent behaviour of on-board power systems, especially DC systems, has not been scientifically explored before. However, such exploration is crucial for the stable and safe operation of future ships equipped with numerous power electronic systems