LEO satellite networks are emerging as a global-scale connectivity infrastructure for regions beyond the reach of terrestrial networks. Among them, satellite IoT targets low-power, low-cost IoT applications; however, our real-world measurements reveal that today's commercial satellite IoT still faces substantial challenges in supporting large-volume data transfer for real-world IoT applications. Our results show that a highly-compressed image of only tens of kilobytes typically takes 6–10 hours, extremely exceeding the application time requirements. We find that the bottleneck lies in the direct-to-satellite upload stage, where usable contacts are scarce and underutilized. Moreover, simply adding more nodes does not provide proportional gains, as beacon-triggered upload opportunities remain isolated and exhibit weak correlation. Based on this observation, we propose Co-DtS, a multi-interface upload system that promotes observed beacons into cross-interface coordination signals. Trace-driven evaluation with commercial devices shows that Co-DtS reduces image completion time from 7.62 hours to 0.9 hours.

Low Earth Orbit (LEO) satellites have emerged as a space-based infrastructure to offer networking services anywhere on Earth. Satellite IoTs enable novel Direct-to-Satellite (DtS) connectivity, allowing IoT devices in remote areas to connect to the Internet via LEO satellites using existing terrestrial technologies like LoRa. This paper presents the first-of-its-kind measurement study on satellite IoTs, investigating the practical characteristics of DtS communications and their suitability for IoT applications. We deployed 27 low-cost ground stations across eight locations worldwide to passively measure the network availability of multiple constellations. Our findings reveal a significant gap between the effective durations of DtS connectivity and their theoretical durations, leading to intermittent connections for satellite IoTs. Additionally, we examine the performance of the Tianqi constellation in supporting real-world IoT traffic (agriculture application). We observed longer delays and higher power consumption in satellite IoTs compared to terrestrial IoTs. Our study identifies the bottlenecks and sheds light on potential optimizations for satellite IoTs.

Almost all existing relevant literatures are focused on the multi-inverter system that only contains one type of inverter. Till now, the interactions in multi-inverter system consisting of polytype inverters have been not investigated systematically. To fill this gap, the paper is aimed at the stability study of the generic system containing multiple types of inverters. The mathematic model of interactions between different types of inverters as well as between the inverter and the power grid are divided into the admittance network and the excitation source. Based on the division stabilities of those interactions are investigated by root locus and a commonly used stability criterion is proposed for the multi-inverter system. To guarantee the system stable, the following two conditions should be satisfied: (a) the admittance network is stable; (b) any two inverters don't have the same unstable poles. The stability of the interaction between the inverter and the power grid is only depended on the criterion (a), whereas the stability of the interaction between different inverters is determined by both conditions. The theoretical analysis is verified by experimental results.

In recent years, with the rapid development of renewable energy, power energy storage has become a bottom neck of its development, and superconducting magnetic energy storage (SMES) seems to be a viable solution. A topology based on common DC voltage bus is proposed for high power voltage source converter (VSC)-SMES. The mathematical model of SMES is constructed and the detailed control strategy is derived. According to the characteristics of SMES, dual mode switching control strategy is adopted. Simulations under different conditions are carried out with PSIM simulation tool. The fast response of SMES and effectiveness of dual-mode switch control are verified by simulation waveforms and the active and reactive power can be controlled independently.