Full
Outline
With increasing penetration rates of power electronic devices into grid continuously, the threat of new-type power system oscillations becomes much serious. On this basis, the mechanism of a particular form of oscillation, i.e., power-frequency oscillation (or called as synchronous-frequency resonance, synchronous-frequency oscillation) is focused. First, by comparative studies on different models of grid-forming converter tied systems by considering or ignoring current-control loop and/or line dynamics, it is found that the power-frequency oscillation can appear in the single-loop grid-forming converter tied systems. Therefore, for the occurrence of power-frequency oscillation, converter should show the characteristics of a voltage source, and meanwhile, line dynamics should be considered. Then, the mechanism of the power-frequency oscillation is studied under a simple model of two voltage sources connected by a dynamical line. Finally, by time-domain analyses of current and power waveforms under the abc three-phase stationary and dq two-phase synchronous-rotating-frame coordinates, it is found that the power-frequency oscillation comes from the un-damping (or weak-damping) transient component (or free component), whereas the inherent power-frequency sinusoidal oscillation comes from the force component. In addition, it is found that the power-frequency oscillation does not show the frequency-coupling phenomenon. The occurrence conditions and physical origin of power-frequency oscillation are revealed directly in time domain. Clearly, all these findings could help understand the power-frequency oscillation and even use power electronic devices better.
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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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