EMI Evaluation and Filter Design of a SiC-Based 3-Level UPS

Uninterruptible power supply (UPS) systems are widely used in data centers or hospitals where continuity of electric power has to be ensured to protect critical loads. The adoption of SiC MOSFETs in the UPS systems enables improvement of both efficiency and power density of the systems. However, more concern on electromagnetic interference (EMI) noise arises because of the high switching speed. Furthermore, the UPS under study is comprised of multiple power conversion stages: rectifier, inverter and dc-dc stage. The EMI mechanism changes with the operation mode of UPS, which complicates the evaluation and containment. In this paper, EMI evaluation and EMI containment with filters have been investigated for a full-SiC UPS comprised of three-level Neutral Point Clamped (NPC) phase legs. An EMI test environment is established for conducted EMI emission measurement under different modulation methods and operation modes. EMI filters are designed to meet the IEC 62040-2 standard and verified with the prototype.