A new DC-ice-melting device based on hybrid MMC structure

In this paper, a new DC ice-melting scheme based on hybrid modular multilevel converter (MMC) is proposed considering the problems of existing DC ice-melting device, such as high harmonic content, complicated mode switching operation, large size and so on. In the scheme, a novel structure of MMC is composed of the upper bridge arm all using full bridge sub-module (FBSM) and the lower bridge arm all using half bridge sub-module (HBSM). In normal operation, the device implement reactive power compensation as static synchronous compensation (STATCOM), and under the condition of grid icing, the device can output continuous controllable DC voltage and current ranging from 0 to the set value for grid ice-melting. In this way, the economic benefits can be improved effectively. The outstanding advantages of the device based on MMC are described, and analysis of mathematical model and power to the structure is presented in this paper. A corresponding hierarchical control strategy is put forward, then feasibility and effectiveness of the scheme and control strategy are verified by simulation in PSCAD/EMTDC.