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The converter with constant-power control in a flexible DC distribution system has characteristics of constant-power load, which will reduce the system damping and adversely affect the system stability. To address this problem, a superconducting magnetic energy storage (SMES) device is introduced to improve the system stability. A feed-back control model of the flexible DC distribution system is derived, and the effect of constant-power load characteris-tics of the converter on system stability is investigated by frequency-domain analysis. Combined with a mathematical model and frequency-domain analysis, it is also pointed out that the SMES device can improve the system stability by introducing positive damping to grid and increasing the phase margin of the system's open-loop transfer function at the shear frequency. To prevent over-high voltage at both ends of the superconducting magnet, the DC/DC converter which connects the SMES device with the DC distribution network needs to have certain voltage regulation performance. Therefore, the SMES device with a modular multilevel DC/DC converter (DC-MMC) is studied, which can adjust the number of sub-modules flexibly to set the voltage ratio of the converter. Moreover, the DC-MMC can control the voltage at both ends of the superconducting magnet while realizing a bidirectional flow of energy in the converter, thus protect-ing storage device. The feasibility and effectiveness of the SMES device with DC-MMC in improving the stability of flex-ible DC distribution system is verified by time-domain simula-tion waveforms.
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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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