When the normal electricity supply, electricity and surge absorption by the loop filter circuit, the same action in two loops, one is through the charging circuit of the battery pack, the other is the rectifier circuit, as the converter input, and then after the conversion converter to provide clean AC power to the load through use; at this time if an exception occurs electricity, the inverter's input has been replaced by a battery pack to supply converters continue to provide electricity, achieve full uninterruptible power. It can be seen on-line uninterruptible power system output entirely by the converter to supply power quality regardless of how the city, its output is stable and pure sine wave power.