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The development of science and technology has brought explosive growth of data volume, which provides great convenience for the operation of enterprises. With the advent of the era of big data, enterprises are more vulnerable to the risk of data privacy leakage when they are transmitting cross-border trade. In this paper, this phenomenon is investigated. Affected by the epidemic situation, we conducted in depth communication with nine different types of enterprises by means of cloud interview. After classifying them, about 30% of enterprises in each category are selected for empirical research through questionaires survey. The results show that the nine enterprises have a weak understanding of the existing laws on data privacy protection at home and abroad. Based on this, after the simulation experiment, this paper puts forward corresponding suggestions for enterprises and government departments, which has certain reference value for related enterprises to formulate privacy policies and strategies in China.

The DC transformer (DCT) based on half-bridge topology is studied in this paper, analyzes the circuit principle of work, on the basis of this, the characteristics of DCT are studied, zero voltage switching (ZVS) is deducted, and the characteristic of the output voltage and power transmission of DCT are given, as well as the design method and optimization design. Finally, ZVS half-bridge DC transformer with 120W prototype is developed, the converter has been verified by simulation and experiment.

Modular Multilevel Converter (MMC) based on full-bridge sub-modules(FB-MMC), which has advantages of outputting negative level, improving the utilization rate of DC voltage and having the capability of fast recovering DC short-circuit faults, can be applied to high voltage and large capacity MMC-HVDC system based on overhead lines. Based on the operation mechanism of FB-MMC, the charging characteristics of two kinds of charging modes including active charging and passive charging, are deeply analyzed , and corresponding soft-start strategies to be selected are given. Through theoretical and simulation comparison and analysis of performances of different soft-start strategies used in each kind of charging mode, the optimized soft-start strategies are proposed, which provide a theoretical basis for engineering design and application of high voltage and large capacity MMC-HVDC with overhead lines.