An Inrush Current Reduction Technique for the Line-Interactive Uninterruptible Power Supply Systems

Abstract

Numerous critical loads of commercial, industrial and domestic use rely on the uninterruptible power supply system to uphold the power during voltage sags and outages and maintain the normal operation. In case of power failure or any disturbance, a UPS system generally takes over load within 1-5 msec in order to supply continuous power to load and avoid any interruption. However, this transition of load can cause significant inrush current phenomenon on the load transformer due to magnetic saturation. The generation of inrush current can cause the reduction of line voltage and sometimes triggering the over current protection of a UPS system. This paper proposes an inrush current reduction technique by supplying rated current to load and energizing the secondary of the transformer to its rated magnetizing current through a current regulated inverter. The possibility of generating inrush current is almost eliminated during any line-line, single phase open circuit and three phase open circuit faults at the prim ary side of the transformer, after energizing the secondary of the transformer and connecting it to the current regulated voltage source inverter. MATLAB is used to obtain simulation results.