The study of ecological security patterns (ESPs) is of great significance for improving the value of ecosystem services and promoting both ecological protection and high-quality socio-economic development. As an important part of the “Loss Plateau-Sichuan-Yunnan Ecological Barrier” and “Northern Sand Control Belt” in the national security strategic pattern, there is an urgent need to study the ESPs on the Loess Plateau. Based on a remote sensing dataset, this study identified the ESPs at different spatial scales, and analyzed the similarities and differences of ecological sources, corridors, and key strategic points, so as to better inform the development and implantation of macro and micro ecological protection strategies. When taken as a whole unit, we identified 58 ecological sources (areas with higher levels of ecosystem services) on the Loess Plateau (total area of 57,948.48 km2), along with 134 corridors (total length of 14,094.32 km), 1325 pinch points (total area of 315.01 km2), and 2406 barrier points (total area of 382.50 km2). When splits into ecoregions, we identified 108 sources (total area of 67,892.51 km2), 226 corridors (total length of 13,403.49 km), 2801 pinch points (total area of 851.07 km2, and 3657 barrier points (total area of 800.70 km2). Human activities and land use types are the main factors influencing the number and spatial distribution of corridors, ecological pinch points, and barrier points. ESPs constructed at different spatial scales are broadly similar, but significant differences among details were identified. As such, when formulating ecological protection and restoration strategies, the spatial scale should be considered. Moreover, specific programs should be determined based on ESP characteristics to maximize the protection of biodiversity and ecosystem integrity from multiple perspectives and directions.

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In the medium-voltage AC/DC distribution networks with distributed renewable sources on islands, a multi-port receiver is the key factor for hybrid power conversion. However, the most used modular multilevel converter (MMC)-based multi-port converters (MCs) face the coordination and complexity challenges due to their double-stage control system and voltage-balancing control of capacitors. In particular, the control system is more unstable and complicated when the control of circulating currents is considered. In this paper, an isolated modular multilevel converter (I-MMC) is used as a receiver, and a unified coordinated control scheme based on the multiple modulation freedoms is proposed. Due to the voltage clamping of high-frequency transformers, there is no concern of the capacitors' voltage-balancing control. Based on the proposed single-stage control system, the unified coordinated control scheme solves the coordination problem of the MMC-based MCs. The multiple modulation freedoms corresponding to an AC port, two DC ports, and three-phase circulating currents can independently control respective targets. The control structure is simplified, while the control freedoms are ensured. Experimental results confirming the performance of the designed control system is shown. INDEX TERMS Circulating currents control, isolated modular multilevel converter, medium AC/DC distribution networks, multiple modulation freedoms, single-stage control system, unified coordinated control scheme.

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