Single-Phase Transformerless Line Interactive Uninterruptable Power Supply with Two Independent Control Algorithms

Abstract

This paper presents the development of two independent control algorithms for an Uninterruptable Power Supply (UPS). It is a mitigation tool to mitigate power interruption. The UPS circuit consists of a bidirectional buck-boost DC-DC converter, a rechargeable battery and a DC-AC/AC-DC converter. The bidirectional DC-DC converter has a function of charging (buck) or discharging (boost) the battery for maintaining DC-link voltage connected to the DC-AC/AC-DC converter. During the normal mode operation, the DC-AC/AC-DC converter supplies voltage to the bidirectional converter by performing AC to DC conversion. Instead, during the backup mode, the converter supplies voltage to the load by performing DC to AC conversion. In this work, a single-loop voltage control algorithm regulates the bidirectional converter. For the DC-AC/AC-DC converter, a multi-loop control algorithm regulates the output current using the inner loop and the output voltage using the outer loop. MATLAB/Simulink simulates the UPS to determine its performance during normal and backup mode operation. From the simulation results, both independent control algorithms can regulate the operation of both converters during both modes of operation. As a result, the UPS system is capable of supplying sinusoidal waveforms with low Total Harmonic Distortion (THD) of output current and output voltage. Both THD values are below 4%.