Analysis of a Single-Phase Line-Interactive UPS System

Abstract

This paper presents an analysis of a single-phase line interactive uninterruptible power supply (UPS) system, allowing output voltage conditioning, such as voltage harmonic suppression and sag/swell compensation. Additionally, the UPS input current is also compensated, allowing current harmonic suppression and reactive power compensation. In other words, the UPS system acts as a true unified power quality conditioner (UPQC), when working in standby operation mode. The power rate handled by both series and parallel PWM converters depend on the operation conditions of the UPS system, such as the amplitude of the fundamental input voltage, the total harmonic distortion of the load current, fundamental power factor of the load, battery charging, among others. In standby mode, the amplitude of the UPS output voltage will be allowed to vary in order to follow the amplitude of the input voltage within a limited range defined by design requirements. This strategy will allow an effective optimization of the efficiency of the UPS system. Mathematical analyses of the single-phase line interactive UPS system are presented in order to obtain the state space models of the two PWM converters. Validation results are presented in order to evaluate the performance of the line interactive UPS system