Full
Outline
In a weak grid, the phase-locked loop (PLL) of a grid-connected converter will dynamically interact with the current loop and further lead to a small-signal (or harmonic) instability problem. To solve this problem, a small-signal modeling method is used to establish an equivalent impedance model of the grid-connected converter. On this basis, the impedance model of the converter is combined with a system stability judgment method, and the instability mechanism of the grid-connected converter under the weak grid condition is analyzed by using the pole variation trajectory and the Bode plot. For a multiple-input multiple-output system, an active damping control strategy based on minimum phase digital filters is proposed while considering multi-loop coupling, so as to improve the system stability margin. At the same time, a specific implementation scheme of the control strategy, a parameter design method and the impact of the control strategy on the multi-loop coupling part are given. In addition, to study the effectiveness of the proposed control strategy under different operating conditions, the system stability margin under the proposed control strategy in the cases of different grid strengths, PLL bandwidths and current loop bandwidths is analyzed, and it is compared with that under the traditional control. Finally, the correctness of the proposed theory was verified by the result of a hardware-in-the-loop experiment.
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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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