国网电力科学研究院有限公司

With the access of high proportions of new energy，synchronous generators are gradually phased out. On one hand，system inertia is reduced. On the other hand，during short-circuit faults，the low-voltage ride-through characteristics of new energy may result in short-term power disturbance，leading to rapid drops in grid frequency. Frequency emergency control，as a critical measure to safeguard frequency stability after grid faults，may encounter issues such as delayed actions or improper control actions resulting in high or low frequency events. To address these challenges，a frequency response model incorporating frequency emergency control is established. The boundaries of emergency control effectiveness under typical conditions are studied. Furthermore，a frequency response model that considers both frequency emergency control and grid-forming new energy is developed. Based on this model，the influence of various frequency control parameters，such as power reserves of new energy and droop control coefficients，on the effectiveness of frequency emergency control is analyzed comprehensively. Requirements for frequency regulation performance of grid-forming new energy to ensure effective emergency control are provided. Finally，the frequency model and the proposed effectiveness boundaries of emergency control are verified using simulations on the IEEE 10-machine 39-bus system. The results show that the participation of grid-forming new energy in frequency regulation can effectively extend the operating boundaries of emergency control，and its power reserve has a significant impact on the upper and lower boundaries of frequency emergency control effectiveness.

The uncertainty of new energy results in power prediction errors, causing new energy producers to bear high wind curtailment losses and deviation penalties due to bidding deviations. To address these issues, this paper proposes a feature-constrained multi-layer perception (MLP) power prediction algorithm, combined with storage-based bilateral transactions, to provide power support and reduce bidding deviations. First, the MLP model is enhanced by improving the relevancy of the hidden layers through adaptive learning, which strengthens its ability to capture nonlinear rules in input data and improves power prediction accuracy. Then, the algorithm allows for bilateral transactions between new energy producers and storage enterprise before entering the day-ahead market, helping mitigate the penalties associated with prediction errors including deviation and curtailment costs. Finally, the case study demonstrates that the feature-constrained MLP effectively improves the power prediction accuracy. Additionally, engaging in bilateral transactions with storage enterprise significantly reduces the costs incurred by new energy producers due to bid deviations.

Extreme weather brings many challenges to the construction and operation of new power system, and the continuous enrichment of the flexible resources of power system provides the power grid new ideas to deal with extreme weathers. Considering the scenarios of energy storage and other resources aggregation participating in power grid load recovery under extreme conditions, a study is made on the strategy and method for resource aggregation participating in power grid resilience improvement. Firstly, based on the operation status of energy storage resources, a resource surplus adjustment ability model is proposed. And then, a resource aggregation regulation model is established considering the resource surplus adjustment ability, and through "domain" characterization of the correlation between the surplus adjustment ability of resource aggregate and operation power, a power grid optimization operation and resilience improvement model is further built. Finally, the effectiveness of the proposed strategy for power grid resilience improvement is verified through case study.

The containerless and solidification method of electrostatically suspended deep subcooled samples is of great significance for materials science research and materials preparation,and this paper proposes to realize the experimental study of triggered nucleation and solidification and measurement of materials under deep subcooling based on the local temperature gradient field of the laser pulse.By trig-gering the laser pulse to generate a local temperature,a temperature gradient is formed around the sam-ple,and the temperature gradient triggers convection to increase the probability of structural and ener-gy undulation inside the experimental sample and deepen the degree,so that the crystals change from a molten liquid phase to a solid phase,realizing high-quality and controllable deep-subcooling laser pulse-triggered nucleation under electrostatic levitation.By means of finite element simulation methods,the ef-fect of laser heating with different spot diameters and a power of 9 W,a power density of 2.86×108 W·m-2 and 1.146×107 W·m-2on the temperature gradient field was investigated.The dis-tribution results of the local temperature gradient field in the molten sample under different laser spot diameters were obtained.A zirconium sample with a diameter of 2 mm was used in the experiment to study the time scale of triggered nucleation of molten samples with different laser pulse widths and sub-cooling degrees under smaller laser beam spot diameters.Based on the classical nucleation theory,the time required for the zirconium samples to move from the substable state of the mother phase melt to the solid phase under different supercooling degrees was obtained by statistically analyzing the data from 16 groups of 20 spontaneous nucleations at different supercooling degrees.On this basis,the experimen-tal study of laser pulse triggered nucleation was carried out at a wavelength of 936 nm with a laser pulse spot diameter of 0.2 mm and a sample of zirconium material.The experimental results show that the time required for nucleation and solidification of zirconium material at a low subcooling of 195 K±3 K is 3/4 times lower than that required for spontaneous nucleation,and that high quality and controllable nucleation can be triggered for molten samples at different subcooling levels.

The Qinghai-Tibetan Plateau is the highest in the world, and it is located in an area jointly influenced by the Indian monsoon and westerly winds. With its unique thermal and dynamic effects and complex topographical features, thunderstorms and convective activities occur frequently in the summer over most of the Plateau. The thunderstorm days in the central and eastern Plateau are similar to that of the southeastern coastal region with the most thunderstorm processes and lightning activities in China. However, the life cycle of thunderstorms over the Plateau is usually shorter, and their convective intensity is weaker, compared with those over prominently lower altitude regions. Thunderstorms over the Plateau not only show unique convective structures, but their electrical characteristics also differ significantly from those of thunderstorms over plain areas. Due to the difficulty of observation in the Plateau regions and the limitations in lightning detection technologies, it remains a challenge to understand the intercloud charge structure and lightning initiation of the thunderstorms over the main body of the Plateau region. By utilizing very high frequency (VHF) broadband interferometer lightning mapping technique, weather radar, and radio sounding, a thunderstorm process that produced two rare "bold- from-the-blue" flashes was observed in the Lhasa area located in the central Plateau. The mechanism of the "bold-from-the- blue" flashes was revealed through accurate mapping of the discharge processes in high spatial and temporal resolution, and the corresponding charge structure characteristics inside the thunderstorm were also retrieved. At the initial stage of the thunderstorm, it exhibited a negative dipole charge structure with an upper negative and bottom positive pattern, which is completely different from the evolution of charge structure in the thunderstorms over prominently lower altitude regions. When the thunderstorm developed into its mature stage, it exhibited a tripolar charge structure stacked with positive, negative, and positive charge regions from the top to bottom of the thunderstorm. These regions corresponded to environmental temperature zones below -30 degrees C, from -30 degrees C to -15 degrees C, and above -10 degrees C, respectively. The "bold-from-the- blue" flashes were associated with the upper dipole. The discharge originally initiated between the central negative and the upper positive charge region, with the positive leader developing downward to the lower negative charge region and the negative leader upward to the upper positive charge region. When the upward negative leader reached the upper positive charge region, it propagated horizontally and got out from the body of the small storm cell. The discharge ultimately became the "bold-from-the-blue" discharge process, spreading away from the cloud body into the clear sky area and striking the ground. The grounding points of the two "bold-from-the-blue" flashes were 3.6 and 3.8 km from the precipitation edge of the storm, respectively. The horizontal scale of the thunderstorm cell was relatively small with positive charge regions in both the upper and lower parts of the cloud. The unbalanced upper dipole in the smaller storm body, where the upper positive charge region was weaker than the lower negative charge region, was the main reason for triggering the "bolt-from-the-blue" flashes. This study not only sheds light on the mechanism of the rare "bold-from-the- blue" discharge process, but also provides direct observational evidence on the diversity of intercloud charge structure and lightning activity characteristics inside the thunderstorm over high-altitude regions.