Diagnosis and Prognosis of LCL Filter in Marine Electric Propulsion Systems

This paper presents an online technique to estimate the capacitance value of the LCL filter integrated with Active Front End Rectifier (AFER) used in marine vessels or offshore drilling/oil rigs. The proposed methodology is simple, robust and requires flux sensors in addition to the existing on-board sensors for grid-voltages, grid- and capacitor-currents measurements. The proposed online methodology is based on the fundamental components of inductor leakage fluxes, grid-voltages, grid- and capacitor-currents, which estimates both inductance and capacitance of the LCL filter. Based on the estimated values of the inductance and capacitance, a technique is proposed to estimate the resonant frequency of the LCL filter under real-time operating condition which can be used to predict the maintenance schedule before any catastrophic failure. The proposed technique has been validated in a laboratory based 11.3kW marine electric propulsion test-rig for 7.7%, 10% and 14% degradation in the capacitance value of the LCL filter under different loading conditions. The estimated capacitance values under real-time operating condition agree with the measured values under offline conditions for various degrees of capacitance degradation and loading conditions.