A Single-Phase Line-Interactive UPS System for Transformer-Coupled Loading Conditions

A line-interactive uninterruptible power supply (UPS) system is one of the important installations implemented by industrial users to provide continuous power to sensitive industrial applications. Such loads often come with isolation transformers for voltage matching and protection purposes. Hence, a line-interactive UPS system experiences a serious problem of transient current when it operates under transformer-coupled loading conditions. The occurrence of this transient current can either impair the apparatus itself or turn on the overcurrent safety devices. In any situation, the interruption of electrical power for sensitive industrial loads is unavoidable. So as to keep the uninterrupted power and to eliminate transient current for industrial applications operating under transformer-coupled loading conditions, we propose a single-phase line-interactive UPS system based on a customary current-regulated inverter. The inverter of the proposed UPS system employs an improved current-regulating scheme implemented in a stationary frame of reference which regulates the load current and never let it to increase than a prescribed value as the transformer-coupled loads are turned on. Laboratory test results obtained under various operating and loading conditions of the single-phase line-interactive UPS system verify the operation of the proposed system.