Abstract
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.
Highlights
During the past few years, problems associated with the power quality has gained much attention
This paper proposes that the occurrence of inrush current associated with the transformer-coupled loads for a singlephase line-interactive uninterruptible power supply (UPS) system can be eliminated by using a current-controlled inverter
The operation of the proposed single-phase line-interactive UPS system is first investigated during all the possible operating conditions i.e., normal, inverter, and compensation modes
Summary
During the past few years, problems associated with the power quality has gained much attention. Installation of series resistors and their operation during powering the load transformer is considered the appropriate solution for the capacitive type of inrush current Under such a condition, a limited current pass from the resistor and charges the capacitor until the voltage across it attains a point that allows the resistor to be shunted out of the circuit by means of a switch. The key motives behind employing this current control scheme are: (1) it is simple and easy to implement when compared to the d-q rotating frame or P + resonant control based schemes, and (2) its performance can substantially be enhanced and the gain limitations led by the PI controller while dealing with AC signals can expressively be abridged by means of a simple feedforward compensation method as presented in [40] This control scheme allows the proposed UPS system to vary its output current based on the rating of the switching load without any inrush current. The performance of the proposed single-phase line-interactive UPS system is confirmed by experimental results obtained under different operating and switching conditions
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