Per-unit design of a transformerless, H-bridge dynamic voltage restorer with closed-loop load voltage and current-mode control

Based on the modeling of a transformerless, H-bridge, double control loops dynamic voltage restorer (DVR), its stability, harmonics compensation capability, load adaptability and response time are both investigated and analyzed in per-unit system, which demonstrate and predict a stable and good compensating feature. Using the per-unit system to design, those system parameters can be applied to other capacity and base voltage systems conveniently and also in a more general manner than the physical unit system. The determination of DVR capacity and the corresponding DC storage capacitance and rating required is also discussed. This research work can also act as a design reference for constructing different capacities transformerless, H-bridge double loops control DVR from 1 kVA to 100 kVA. Finally, simulation and experimental results are presented to validate the per-unit design method and demonstrate its good system performance.