Design and control of a three-phase four-leg inverter for solid-state transformer applications

This paper proposes the use of a three-phase four-leg (3P4L) converter in combination with an LCL filter for the inverter stage of a solid state transformer (SST). This configuration gives full control over the line-to-line, as well as the line-to-neutral voltage and currents, while providing exceptional harmonics mitigation. A procedure to calculate the passive components for the LCL filter is presented, as well as a method to reduce resonance caused by the filter. Furthermore, two feedback control schemes are derived and are enhanced with a feedforward control scheme.