Low-Frequency Conducted Emission of Electromagnetic in Interferences in Ship Power Systems
Muhammad Sudrajat is a PhD student in the department Power Electronics. (Co)Promotors are prof.dr.ir. F.B.J. Leferink and dr.ir. D.J.G. Moonen from the faculty of Electrical Engineering, Mathematics and Computer Science (EEMCS), University of Twente and prof.dr.ir. R. Smolenski of the University of Zielona Gora, Poland.
The global shift toward sustainable energy has significantly increased reliance on electrical energy conversion, leading to the widespread use of switching-based power converters and other non-linear loads across various applications, including in ship electrical systems. Although these technologies support energy efficiency and enhance control capabilities, their high-speed switching (characterized by rapid, i.e., high dV/dt and dI/dt) generates conducted electromagnetic interference (EMI). The frequency range of 2 kHz to 150 kHz is raising concerns as many power converters operate within this range for their switching frequency. In both commercial and naval ships, conducted EMI often disrupts power quality and poses challenges in fulfilling EMC requirements.
Due to the high cost and limited availability of marine-certified equipment, many ship system integrators opt to install commercial off-the-shelf (COTS) devices onboard. However, these devices are not originally designed for shipboard electrical conditions, which typically have an isolated terra (IT) configuration. This introduces significant EMI challenges, particularly noise that propagates through conductive parts and parasitic capacitances.
Therefore, this thesis aims to get a better understanding of the underlying problem by investigating the distribution and behavior of EMI generated by COTS equipment in shipboard electrical environments, and thus to design and implement corrective measures. It begins with a systematic literature review of scientific databases such as Scopus and Web of Science (WoS) to analyze research trends of conducted emission (CE) issues in ships over the past 23 years. Then examines CE behavior using a multipoint measurement technique, allowing simultaneous observation across multiple locations. It further explores the impact of integrating COTS equipment into ship power systems and characterizes the EMI behavior of COTS-based systems under ship-specific power quality disturbance. The findings indicate that COTS equipment contributes to harmonics and noise above 2 kHz, primarily associated with the non-linearity of pulse-width modulation (PWM) switching. Additionally, shipboard power quality disturbances, such as voltage sags, swells, and frequency deviations, further impact the CE behavior of COTS-based systems. Notably, frequency deviations in uninterruptible power supply (UPS) systems of ship electrical systems can induce amplitude modulation, leading to current beats and sideband noise, and even to spontaneous switching-off, thus causing electromagnetic disturbance. The study also examines the role of parasitic capacitance in common mode (CM) current distribution within shipboard electrical systems. High ground impedance of IT systems makes CM currents tend to flow through parasitic capacitance, making parasitic capacitance distribution a key factor in EMI propagation in ships. To address these challenges, a mitigation strategy for EMI suppression in ship power systems is proposed. This method has been successfully implemented on an actual ship. Research in this thesis offers insights into managing CE when integrating COTS equipment into ships, helping reduce EMI disturbances in onboard systems.
