Reactive-Power Compensation in a Single-Stage Differential-Mode Solid-State Transformer

Isolated single-stage solid-state transformer (SST), which employs zero-voltage switching (ZVS) for high-efficiency operation, generally has limited capability for supporting reactive load. In this article, a novel technique is proposed for a single-stage differential-mode SST (DM-SST), which supports reactive-power compensation in such non-unity-power-factor loads. A pulsewidth modulation active-clamp (PAC) Ćuk converter is used for the DM-SST modules to employ the technique. The PAC-Ćuk converter utilizes clamp circuits across the two main switches, each consisting of an auxiliary capacitor and a switch operating complementarily to the main switch. Addition of the clamp circuits provide ZVS operation on all the switches. In this article, the duty cycles of the switches are varied using a feedforward control to also support the reactive power. Furthermore, the output power relation of the DM-SST for the extended range of control parameters, duty cycles of the main switches, and the phase-shift ratio between the main switches is studied. A design guideline of the DM-SST supporting the reactive load is also presented using the extended output power relation. A 1-kVA hardware prototype of the DM-SST is built using the underscored design guideline to validate the analysis and the operation of the DM-SST.