Mitigating Nonlinear Harmonics in Diesel Electrical Ship Network by Model Predictive Control

Ravindra Sharma, Dr. Chandrakant Sharma

Abstract: The challenge of mitigating harmonics in diesel electrical ship networks is due to the presence of non-linear loads. The main source of harmonics in the power network is the rectification circuits of the Variable Frequency Drives (VFDs) used for propelling the engines. There are various VFDs in use today based on the power level, pulse rate, and the architecture of the system, as well as the type of rectifier diodes, each of which produces different levels of harmonic currents. International and national standards require limiting Total Harmonic Distortion (THD) at the points of common coupling at the bus level in ship networks. Dynamic filtering is an effective solution for harmonic mitigation that can enhance the performance of the system. However, active filtering methods that aim to supply the smaller local harmonic components to non-linear loads to ensure the output contains only the fundamental component are not enough to mitigate harmonic pollution in the rest of the power system. As a result, local load compensation has become the main tool for active harmonic filtering. With all the activities contributing to the compensation concept, there is room for further optimization. Active filters, with their fast harmonic current dynamic performance, can benefit from performance optimization methods to adjust the current sampling rate in response to changing spectral circumstances. The system-level optimization technique will create a harmonic current reference that will induce the ideal current harmonic distribution needed to reduce THD on all the system buses.

Keywords: harmonic mitigation, diesel electrical ship networks, Variable Frequency Drives, Total Harmonic Distortion, active filtering