Performance of a single-stage UPS system for single-phase trapezoidal-shaped AC-voltage supplies

Abstract

A high-performance single-stage UPS system for single-phase AC power supply systems is presented. The topology generates a trapezoidal-shaped load voltage that is synchronized with the AC supply; therefore, a small DC-link capacitor is required. This feature leads to a high-input power factor (0.94 at nominal voltage), and due to the single-stage structure, high efficiency (93% at nominal voltage) is also achieved. Moreover, in both cases the supply current spectrum presents low-order harmonics, all of which satisfy IEC 555. The high performance is validated using both resistive (linear) and diode RC (nonlinear) loads. The dynamic performance of the UPS system is also analyzed under different transient conditions. Specifically, the supply to battery, battery to supply transition, load transient, and supply/battery-voltage transients are performed. They show a transfer time of 500 /spl mu/s (from AC supply to battery) and overvoltages of at most 15%. The dynamic and static evaluations are performed on a 1 kVA UPS system. The design guidelines for the key components and control parameters are also included.