Second Harmonic Ripple Voltage Suppression for Single-Phase ISOP Solid-State Transformer by Active Power Decoupling
Tianyu Wei, Andrea Cervone, Dražen Dujić
Abstract
The solid-state transformers with input-series output-parallel structure are considered for various applications where MVAC to LVDC conversion is needed. However, due to the inherent second harmonic pulsating power in the single-phase AC system, large DC link capacitors are required to smooth the voltage ripple of all floating cells, which reduces achievable power density. The active power decoupling method can shift away the pulsating power from the DC link capacitors, leading to a significant reduction to the DC link capacitance and resulting voltage ripple. So far, the application of active power decoupling is limited to single-level converters, and little research on the impact in modular converters has been done. This paper investigates the feasibility of applying active power decoupling to solid-state transformers. The active power filter with dc-split-capacitor circuit is selected to minimize the DC link capacitance. Simulation results show that the active power filter can significantly reduce the second harmonic voltage ripple and the total DC link capacitance of the SST. A prototype of the active power filter has been built and tested to verify the design.