Full
Outline
DC-DC converters are key devices for realizing the interconnection of high voltage direct current (HVDC) networks with different voltage levels and line topologies. Owing to their advantages such as increasing the controllability of power grid and enhancing the power flow control, voltage regulation and fault blocking capabilities of power grid, DC-DC converters have become one of the research hotspots with the gradual construction of novel power systems, among which the DC modular multilevel converter (DC-MMC) is an effective and non-isolated method for interconnecting HVDC systems with the same line topology. However, DC systems in practice often have large differences in voltage levels and line topologies. In this paper, a novel control strategy for a flexible DC-MMC is proposed, which can realize the interconnection of HVDC systems with different line topologies, such as bipolar and symmetric monopolar interconnection. First, the characteristics of different line topologies in a HVDC transmission system are introduced in detail. Then, a mathematical model including variable transformation is established for the novel DC-MMC, and a control method based on an average bridge arm model and simplified DC grid is put forward. Finally, the simulation results in MATLAB/Simulink show that the proposed method can guarantee the normal operation of DC-MMC in both the normal and degraded modes.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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