Series-parallel resonant UPS with capacitive output DC bus filter for powering HFC networks

This paper presents a single high-frequency transformer full isolated uninterruptible power supply based on series-parallel resonant converters for powering hybrid fiber-coaxial networks. The proposed UPS provides galvanic isolation for the load and the battery, and operates with high input power factor while producing a trapezoidal output voltage waveform either at 60 Hz or at 1 Hz. Small size and light weight are achieved without penalizing the overall efficiency by operating at high frequency and by ensuring zero voltage switching (ZVS) under the different operating conditions. In addition, it is demonstrated that by using a capacitive output DC bus filter it is possible to reduce the current stresses during the backup mode by the appropriate selection of the transformer turns ratio. A design procedure for the selection of the key resonant circuit parameters is developed and exemplified. Experimental results obtained from a laboratory prototype demonstrate the overall performance of the system.