LVDC distribution networks have the potential to release larger capacity without having to upgrade the existing cables. One of the main challenges of LVDC networks is the extra customer-end DC-AC conversion stage. This paper proposes and evaluates a 5-level Si MOSFET-based MMC as a promising alternative to the conventional 2-level IGBT-based converter. This is due to the comparatively higher efficiency, power quality and reliability, and reduced EM emissions. A comprehensive analysis of a Si MOSFET 5-level MMC converter design is performed to investigate the suitability of the topology for LVDC applications. Detailed theoretical analysis of the 5-level MMC is presented, with simulated and experimental results to demonstrate circuit performance. To suppress the AC circulating current, especially the dominant 2nd harmonics, this paper presents a double line-frequency PI with orthogonal imaginary axis control method. Comparison of simulation and experimental results with those for double line-frequency PR control shows that the proposed PI controller has better performance. In addition, it is simpler to implement and more immune to sampling/discretisation errors.
- converter design
- current suppression control
- PI with orhogonal imaginary axis