A Single Phase Uninterruptible Power System with a Gradationally Controlled Voltage Inverter

We have developed a gradationally controlled voltage inverter which is capable of outputting a high-precision waveform even at low switching frequencies and have succeeded in putting it to practical use. This inverter uses plural inverters which have a binary or ternary DC-link voltage ratio with one another, and are connected in series to output the sum of their output voltages. The waveform of the resultant output voltage is quasi-sinusoidal. In this paper, a new UPS applying this technology is explained. The UPS with the high efficiency of 97% and the thin size of 29 mm/kVA has been realized by the miniaturization of the LC output filter and the loss reduction of the power devices