HARMONICS MITIGATION IN A LARGE-SCALE GRIDCONNECTED FUEL CELL STACK

A fuel cell inverter is a source of harmonics as its output voltage and current are not pure sine waves. A direct connection of such power unit into the grid may deteriorate the grid power quality and even affect its stability. Standards such each IEEE 519 and IEC 61000-3-6 set the current and the voltage harmonic distortion limits that a grid-connected power generating unit must not exceed, based on the current and voltage level. This paper deals with the design of an LCL filter to reduce harmonics produced by a three-level inverter serving as an interface between a fuel cell stack and a grid. The grid connected inverter is supplied from a 1.4 MW solid oxide fuel cell stack at 1400 V and operate at an efficiency of 86%. To assess the performance of the filter, the grid-connected system composed of a 1.4 MW fuel cell stack, an inverter, an LCL filter, a grid and a load is simulated using Matlab/Simulink environment. Results show that the designed filter reduces the total harmonic distortions of both voltage and current up to 0.01 %