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This paper presents parallel operation of inverters grid-connected fuel cell systems inaccordance with IEEE1547-2018 category3. The grid code regulations are becoming stricterdue to the increasing amount of the new and renewable energy generated. Therefore, thesenew requirements need to be complied with. The current fuel cell system has its limitationsto conform with IEEE1547-2018 category3. In order to solve this problem, a separateinverter is required, which is connected in parallel with the PCS of the fuel cell system. Theinverter connected in parallel can be operated in two different modes. Constant current modeis applied when the grid is stable, while constant voltage mode applied when the grid isunstable. The control strategy for the parallelly connected inverter in fuel cell system isdiscussed and verified by simulation.