An inrush current reduction technique for the line-interactive uninterruptible power supply systems

Numerous sensitive loads of commercial, industrial and domestic use depend upon an uninterruptible power supply (UPS) system to ensure uninterrupted, reliable, and high quality power during outages as well as over voltage and under voltage conditions to maintain healthy operation. In case of a power failure or other disturbance, a UPS system generally takes over the load within a few milliseconds in order to supply continuous power to the load and avoid any interruption. However, due to the magnetic saturation of the load transformer, this transition of load can cause significant inrush current generation. The generation of inrush current can cause the reduced line voltage and activate the over current protection of a UPS system. This paper proposes an inrush current reduction technique by supplying the rated current to the load and energizing the secondary of the transformer to its rated magnetizing current through a current regulated voltage source inverter after connecting it to the secondary of transformer. The possibility of the generation of inrush current is almost completely eliminated during all possible loading and transient conditions. Simulations have been performed by using simulink to validate the proposed inrush current reduction technique.