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

• Published in: IET generation, transmission & distribution transmission & distribution, 2018-08, Vol.12 (15), p.3626-3636
• Main Authors: Elserougi, Ahmed A, Massoud, Ahmed M, Abdelsalam, Ibrahim, Ahmed, Shehab
• Format: Article
• Language: English
• Subjects: BC output stage; BC switch; bidirectional hybrid modular nonisolated DC‐DC converter; closed loop systems; closed‐loop controller; DC‐DC power convertors; half‐bridge submodules; HB‐SMs capacitors; high conversion ratios; high‐voltage side; load flow control; low duty cycle; low‐voltage side; medium‐voltage DC grids; power 2.5 MW; power capacitors; power flow control; power grids; Research Article; self‐balanced nonisolated hybrid modular DC‐DC converter; self‐balancing operation; sequential connection; voltage 10 kV; voltage 25 kV
• ISSN: 1751-8687; 1751-8695; 1751-8695
• DOI: 10.1049/iet-gtd.2017.1813

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 (HB-SMs) 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 closed-loop 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.