A Study on CMV Characteristics According to Output of ESS During Charging and Discharging

Recent fire incidents in large-scale ESS(energy storage system) have raised concerns about the electrical risks inherent in their operation. Specifically, the CMV(common mode voltage) generated by the PCS(power conversion system) in ESS can impose continuous electrical stress on the battery and DC circuits, potentially leading to severe issues such as battery insulation failure and increased electrical noise. CMV primarily arises from interactions between switching components and parasitic capacitance, and this phenomenon becomes more pronounced in large-scale ESS, accelerating battery degradation and increasing the risk of fire hazards. This study analyzes the mechanisms of CMV generation in ESS and quantitatively evaluates CMV variations during charging and discharging processes through linear regression analysis. By modeling the relationship between ESS output power and CMV, system degradation and potential risks are predicted by examining CMV fluctuations during operation. Experimental results indicate that as charging power increases, the CMV magnitude also rises, intensifying electrical stress on the battery and DC circuits, while CMV decreases during discharging. These findings suggest that CMV trends can serve as indicators for early detection of system abnormalities by comparing them with trends observed in healthy systems. This approach has the potential to enhance ESS safety and help prevent incidents such as fires by identifying potential risks in advance.