Efficiency improvement in soft-switching three-level converters for high power UPS

Efficiency of high power Uninterruptible Power Supplies (UPS) is a fundamental criterion regarding the permanent use of such a device. A state of the art on soft-switching over constraint of the UPS application has been made. The principle of Auxiliary Resonant Commutated Pole (ARCP) using autotransformer has been identified as the most interesting way to increase efficiency or switching frequency. Its application for multi-level converters has been studied. A simplified resonant pole has been proposed for both three-level rectifier and inverter used in UPS. The design criteria have been discussed. A single phase of a 125 kVA three-level UPS has been realized and tested. The concept has been validated.