Power Quality Assessment in Shipboard Microgrids Under Unbalanced and Harmonic AC Bus Voltage

Abstract

Abstract-Power quality (PQ) is becoming more and more critical issue in shipboard microgrid systems (SMG). Especially, the impact of voltage unbalance combined with harmonic distortions on the SMG behavior has not been fully investigated. In this paper, simple power quality assessment models and a series of controlled experiments are proposed and carried out in a real ship under seagoing conditions. The ship experimental results are presented and discussed considering non-linear bow thruster load and high power ballast pump loads under unbalanced and harmonic voltage conditions. In addition, the analysis of bow thruster current harmonic surges during the ballast pump start-up is presented. Furthermore, the voltage/current distortions of working generator, bow thruster and pump loads are analyzed. The paper provides a valuable analysis for coping with PQ issues in the SMG.

Review of Power Quality Issues in Maritime Microgrids

“…In addition, it can also result in other undesirable consequences, such as thermal aging of insulation, overheated bearings and reduced efficiency of equipment operation. An experimental study [37] where a single phase of a 3-ph heating load was disconnected to emulate an unbalanced load concluded that the harmonic distortion phenomenon during both steady state and transient operation phenomenon is more significant when voltage imbalance is present in the system. In the aforementioned experiment, the voltage THDs were in the range of 6.52%-6.73%, whereas for the unbalanced condition (imbalance factor u2=1.76%), the range of the THD changed to 6.15-7.38% depending on the line-to-line voltage [37].…”

“…An experimental study [37] where a single phase of a 3-ph heating load was disconnected to emulate an unbalanced load concluded that the harmonic distortion phenomenon during both steady state and transient operation phenomenon is more significant when voltage imbalance is present in the system. In the aforementioned experiment, the voltage THDs were in the range of 6.52%-6.73%, whereas for the unbalanced condition (imbalance factor u2=1.76%), the range of the THD changed to 6.15-7.38% depending on the line-to-line voltage [37]. In more severe cases, faults occurring in certain portions of shipboard power systems can also bring about voltage dips or spikes [25].…”

Hardware-in-the-Loop Methods for Stability Analysis of Multiple Parallel Inverters in Three-Phase AC Systems

“…A N increasing number of applications of AC-distributed power systems have been made possible due to advances in semiconductor technologies and inverter topologies. These applications can be found in several new and emerging fields, including renewable energy generation [1], hybrid and electric vehicles [2], smart grids [3], electric aircrafts [4], and electric ships [5].…”

Comparative Case Study on Oscillatory Behavior in Power Systems of Marine Vessels With High Power Converters

“…Frequency fluctuations can also lead to undesirable resonances and cause crucial equipment such as measuring instruments to malfunction, while the effects of poor voltage profile include problems such as lamp flicker. A worst case scenario of partial or total blackout of the power network endangering the safety of man and machine onboard can also result from these power quality issues (Xu et al, 2006;Prousalidis et al, 2007;Prousalidis et al, 2009;Jayasinghe et al, 2018;Liu et al, 2019). The problem of instantaneous frequency modulation is recognized by some ship classification societies such as Lloyd Register of shipping which stipulates limits on "a maximum rate of change of frequency not exceeding ±1.5 Hz per second during cyclic frequency fluctuations" (Lloyd's Register, 2019).…”