Self-balanced non-isolated hybrid modular DC-DC converter for medium-voltage DC grids

Abstract

Here, a new bi-directional hybrid modular non-isolated DC-DC converter is proposed where it consists of a boost converter (BC) fed from the high-voltage (HV) side. At the BC output stage, a certain number of half bridge submodules (HBSMs) is connected across the BC switch. During the turn-on period of BC switch, the HB-SMs are connected sequentially to the low-voltage (LV) side, which results in charging/discharging their capacitors from/into the LV side. While, during the turn-off period, the LV side is bypassed and the HB-SMs capacitors are connected in series across the BC output stage, which results in discharging/charging them into/from the HV side. The power flow is controlled in both directions by controlling the duty cycle. The proposed configuration provides self-balancing operation thanks to the sequential connection of HB-SMs capacitors, and it also provides the ability to operate with high conversion ratios. Illustration and analysis of the proposed converter and its closedloop controller are presented. A full design of the values and ratings of the involved components are presented. Simulation study for a 2.5 MW (25 kV/10 kV) DC-DC converter is presented. Finally, experimental results for a downscaled prototype are presented for validation.