Single-Phase Five-Leg AC-DC-AC Multilevel Converter to Enhance Power Quality

This paper proposes a single-phase ac-dc-ac multilevel converter composed of a three-leg module series-connected to an H-bridge at load side of the system to achieve a higher and multilevel voltage at the output converter. The proposed system is appropriate for applications with same input and output frequencies to enhance power quality, such as uninterrupted power supply and unified power quality conditioner, and for electric power conversion systems in which the output voltage required is twice the input voltage, without isolation transformer. Circuit model equations, power flux analysis, dc-link voltage specifications and a PWM strategy based on vector approaches are discussed. The proposed system control ensures fixed load voltage with constant amplitude and frequency, maximizes the grid power factor and regulates the dc-link voltages. Compared with conventional, proposed topology has lower dc-link voltage rating, lower harmonic contents and lower power losses. Simulation and experimental results demonstrate the operation of control system and validate the theoretical studies.

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