Line-Interactive Transformerless Bidirectional Buck-Boost Uninterruptable Power Supply System With Battery Control Algorithm

Abstract

This paper presents integrated control algorithms for a single-phase line-interactive transformerless bidirectional buck-boost Uninterruptable Power Supply (UPS). The control algorithms consist of two battery control algorithms and one dc to ac conversion algorithm. The battery control algorithms are applied to a bidirectional buck-and-boost converter. Additionally, an AC/DC-DC/AC converter employs the dc to ac conversion algorithm. The battery control algorithms utilise two Proportional-Integral (PI) controllers to regulate voltage and current, respectively. In contrast, the dc to ac conversion algorithm applies one PI voltage controller and a bandless hysteresis current controller. The battery reference value is set according to the battery’s fully-charged voltage for the battery charging control algorithm. Meanwhile, the dc output voltage is set higher for the battery discharging control algorithm to allow the success of dc to ac conversion by the AC/DC-DC/AC converter. Based on the simulation findings, both independent control algorithms can govern the functioning of both converters in both modes of operation. Consequently, the UPS system can supply sinusoidal voltage and current waveforms with low Total Harmonic Distortion (THD) output.