Transformerless Uninterruptible Power Supply with Reduced Power Device Count

摘要

This article presents a transformerless off-line uninterruptible power supply with a reduced power device count. The operation of the proposed uninterruptible power supply is divided into two modes. The first is the charging mode, where a pulse width modulation rectifier and a buck converter are controlled to charge the battery bank with a sinusoidal supply current at a unity power factor. The second mode is the inverting mode, where a boost converter is used to regulate the DC-link voltage to a level suitable for a sinusoidal pulse width modulation inverter to generate the rated load voltage. The inverter is working at a constant modulation index to provide a high-quality output voltage to the load during the interruption. The use of buck and boost converters eliminates the need for a transformer to adjust the DC voltage level for the charging process or the AC voltage level across the load. A hardware setup is implemented to evaluate the dynamic behavior of the proposed uninterruptible power supply system. Furthermore, the proposed uninterruptible power supply system is simulated using the PSCAD/EMTDC (Manitoba, Canada) software package. Several test cases with different load types are conducted to study the effectiveness of the proposed control system. Accurate performance and fast dynamics are revealed from both the simulation and experimental results.