Analysis and mitigation of circulating common mode current in large-scale PCS-integrated ESS sites

This paper presents an analysis of common mode current (CMC) problems at a large-scale energy storage system (ESS) site with power conversion system (PCS) rated at approximately 80 MW. The site experienced significant troubles such as IGBT damage and sporadic shutdowns, which may be caused by CMCs. A series of measurements were made to find the root cause of the CMC, and the field data were studied through the analysis based on the common mode equivalent circuit. Meanwhile, the variation of the resonance peak of CMC was considered for different operating conditions. As a result, it has been clarified that the main flow path of the CMC includes a wye-connected capacitors (YCAP) installed as an electromagnetic compatibility (EMC) filter. In addition, the parameters of the system could be obtained and applied to the derived equivalent circuit. It has been verified that the frequency analysis results via Bode plot and field measurement were in close agreement. Finally, the hardware-in-the-loop simulation (HILS) was executed with the derived parameters. The HILS results strongly aligned with the actual measurements, confirming the accuracy of the simulation model. Finally, the preview hardware-in-the-loop (HIL) test showed that the elimination of YCAP significantly reduces the CMC. The effectiveness of YCAP removal was also shown in the field. This study could provide valuable guidance for addressing similar issues that may arise in future large-scale ESS installations.