A Study on Modeling of Ferro-resonance Characteristics with Saturation of Grid-connected Transformer in Energy Storage System

Battery system might be severely effected by unexpected ferro-resonance phenomenon in Li-ion battery based ESS, which is energetically installed and operated in large scale way. Therefore, this paper defines mechanism of the ferro-resonance phenomenon with L-C series and series-parallel combination circuits, which is regarded as one of electrical hazards, and proposes characteristics of the ferro-resonance through graphical solutions and equivalent circuit. And also, this paper proposes an algorithm to prevent ferro-resonance phenomenon in the interconnected transformer that can avoid the ferro-resonance by calculating appropriate capacity of PCS filter based on the presented ferro-resonance characteristics. Furthermore, this paper performs modeling of ESS based on PSCAD/EMTDC, which is composed of 3-phase power supply system including circuit breaker and interconnected transformer, PCS(power control system) and battery system. From the simulation results based on the proposed modeling, it is confirmed that secondary voltage of interconnected transformer for ESS can be rapidly increased due to the ferro-resonance phenomenon in L-C series and series-parallel combination circuits and then the battery system may be severely affected by such rapid over-voltage. And also, it is confirmed that the proposed prevention algorithm of ferro-resonance can contribute to stable operation of ESS by installing optimal capacity of filter in PCS.