A Two-Phase Five-Level Converter With Least Number of Power Switches Requiring Only a Single DC Source

A novel single dc source fed five-level converter topology for medium-voltage high-power isolated grid-tied systems requiring only 12 power switches is proposed. The present configuration has two stages namely, five-level converter and the Scott-T transformer. The five-level converter stage generates only two phase voltages. Latter, these voltages are converted into three phases by using the Scott-T transformer connection. This topology requires less number of power devices and its associated gate drivers in comparison to any existing topology. In addition, the dc-link capacitors used in the topology have an ability to self-balance by themselves which eliminates the requirement of capacitor balance circuitry and complex control algorithms. The overall component count in the present configuration is very less in comparison to other topologies. Further, each device in the converter is stressed to only half of the dc-link voltage. A level-shifted carrier pulsewidth modulation scheme is adopted to control the converter, and proportional integral controllers are used to inject current into the grid at unity power factor. Theoretical analysis and simulation of the proposed converter are performed and a prototype with 1 kVA rating is validated by connecting it to a three-phase grid.