Highly efficient DSP-driven inverter based on a novel symmetrical flux forward converter

Reliable AC back-up fed by the 48 Vdc battery source are in a continuous evolution. The market's need drove us to develop a new topology of DC/DC converter integrated in a full digital control inverter. It has been done at first on a 2U'/1 kVA unit and a 1U'/300 VA unit both naturally cooled as well as a 3 kVA unit forced air of 2 U'high, outputting 120 Vac or 230 Vac. One of the best ways to get the proper AC availability level is to increase the MTBF of the unit. Well-known means to improve the MTBF are the decreasing of part-count number and a lower working temperature. A more than 90% overall efficiency has been achieved with a new isolated DC/DC converter called the "symmetrical flux forward"(SFF), stepping up the input voltage from 48 Vdc (in the range of 40 up to 80 Vdc) to 350 Vdc. This improved topology has a very low part-count and many other advantages. The low part-count condition has been fulfilled too by applying the most recent technologies in an inverter. In fact, digital signal processing (DSP) and field programmable gate array (FPGA) technologies become a possible and interesting solution to overcome the inverter control barrier. Closing all control feedback loops in the digital signal processor gives us also a temperature dependency compensation of analog devices, a very low part count, an efficient active filtering to comply with telecom standard and an automatic board self checking at the manufacturing time. This paper presents the state of the art in the inverter technology and a new DC/DC converter topology leading to a smart AC solution.