Low frequency UPS technology appeared in the 70s of last century, its rectification frequency and work frequency is the same. Limited to the development of semiconductor technology, the breakdown voltage of IGBT in inverter can only achieve 600V, so the bus voltage is limited, the output voltage of the inverter can not achieve 380V; and the low frequency inverter is the full bridge circuit, the output for the three-phase line, unable to meet the demand of single-phase IT load and four wire and three-phase load, must be Δ-Y conversion. In order to solve these problems, the manufacturers add the transformer in the low frequency inverter output side to elevated the voltage and generate the central line, so that the to meet the requirements of the output voltage of the load, which is the real purpose of the low-frequency built-in transformer.
By the 90s of the last century, the third generation trench IGBT was invented, its ability to enhance the withstanding voltageto 1200V, prompting the innovation of UPS technology. The bus voltage is increased to 700V through the rectifier side high frequency boost circuit, the output voltage of the inverter can be 380V, and the output transformer is canceled. And this rectifier inverter circuit works in the high frequency (several kHz or more) and no output transformer is called high frequency intelligent UPS.
