A Systematic Power-Quality Assessment and Harmonic Filter Design Methodology for Variable-Frequency Drive Application in Marine Vessels

In maritime industry, high fuel costs encourage use of variable-frequency drives (VFDs) for energy-saving applications. However, introduction of such nonlinear loads in the vessel´s power distribution network induces harmonics, which can lead to potential risks if are not predicted and controlled. In this paper, a systematic power-quality assessment and monitoring methodology is proposed to calculate VFD contribution to voltage distortion at the point of common coupling (PCC), considering the source short-circuit capacity and the existing vessel´s power system harmonics. According to voltage harmonic distortion limits set by marine classification societies, design and sizing of appropriate harmonic attenuation filters is made, including ac and dc chokes and frequency-tuned passive filter options. The effectiveness of the proposed power-quality analyzing procedure is evaluated through a real practical example, which includes harmonic filter design for VFD retrofit application to fan and pump motors that operate constantly during sea-going operation in a typical tanker vessel. Power-quality field measurements obtained through a harmonic monitoring platform implemented on board verify that total voltage harmonic distortion and individual voltage harmonics at PCC are maintained below 5% and 3%, respectively, showing that design complies with relevant marine harmonic standards even in the worst operating case.