High efficiency multilevel uninterruptible power supply

This paper presents a multilevel double conversion uninterruptible power supply (UPS) for higher efficiency and effective size/weight reduction. The main circuit of this UPS features a transformerless three-level circuit topology resulting in high double conversion efficiency (over 96%) and considerable size/weight reduction. This design also includes a customized IGBT power module and a double bidirectional chopper. The customized IGBT module reduces parasitic inductances and hence improves reliability by lower electrical and thermal stresses. The double bidirectional chopper reduces ripple current and then also offers a contribution to UPS compactness. Test results using a 225 kVA-prototype confirm the improvement in efficiency and the high performance of the proposed UPS.