Papers by Keyword: DC Voltage

Abstract: This paper discusses the establishing method of DC voltage of modular multilevel converter (MMC). Firstly the structure of MMC and the charging principle of sub-modules (SMs) are introduced in order to control the DC voltage of MMC and reduce the switching loss. It is pointed out that the DC voltage control in MMC includes two parts, the DC voltage establishment of system and the voltages control of SMs. For the DC voltage control in system, the control theory is analyzed, and the corresponding control strategy is proposed. Meanwhile an improved voltage balance control strategy for SM is proposed by the improvements of the traditional voltage sorting method to reduce the high switching frequency caused by the blind action of switching devices in the SM control. Finally, the simulation results based on PSCAD/EMTDC show that DC voltage in MMC can run in the rated value steadily, and the switching frequency is reduced significantly.

Abstract: In the present study, dc high voltage was applied to produce droplets with controlled diameter in wide range. The dc voltage was ranged from 0 to several kV. Water glass was atomized in alcohol solution into diameters of several ten μm, depending on dc voltage applied between nozzle and ground electrode. The atomized water glass droplets were solidified by removing water molecules from the water glass. When the dc voltage was raised, nozzle diameter and electrode distance were decreased, the diameter of silica particles was decreased.

Abstract: Some flashover incidents of high-voltage transmission lines are reported to be induced by fire. Though the mechanism of fire induced flashover is not well understood, it is deemed that fire could reduce the insulation strength of air. This paper has compared the breakdown characteristics of gaps in normal air conditions and those in fire. The results show that the breakdown voltage or electric field strength of gaps in fire decreases greatly. The value of breakdown electric field strength in alcohol flame is about 1.454 KV/cm, which is only about 28.8% of that in air. The value of breakdown electric field strength in wood crib fire is about 0.300KV/cm, corresponding to 19.9% of that in air. This study demonstrates that flame and soot particle of fire are responsible for fire induce flashover of high-voltage transmission lines.

Abstract: Differing with the traditional way to perform electroporation (EP) by using the DC electrical pulse, this paper proposes a new EP system by applying continuous DC voltages to generate proper EP electric field strengths utilizing the shape change of the channel. The fabrication of chip and set-up of system are clearly described and simulations also carried out utilizing CFD-ACE to study the electric field strength distribution and the time span when fluid passes through different electric field strengths. The fabrication of the proposed EP system is quite simple and low-cost.