The capacitance of submarine cables with the same length and the same voltage level is more than 20 times that of overhead lines, which makes the reactive power for AC transmission system of offshore wind power greatly increase and the power flow is complicated, and it is easier to produce a series of problems such as reactive power return, low power factor, increased network loss, and terminal voltage rise, which puts forward higher requirements for reactive power compensation configuration scheme. Combined with practical engineering cases, this paper introduces the reactive power and voltage characteristics of the sea breeze system, as well as the problems and shortcomings of conventional reactive power compensation schemes. Finally, the reactive power allocation optimization scheme based on the new magnetically controlled controllable reactor MCR is proposed, which has the technical and economic advantages of low running loss, saving investment and land occupation, etc. It can be used as a beneficial supplement to the reactive power allocation scheme for the transmission system of offshore wind power with AC cable and has the value of engineering popularization.

Concerning the incorrect operation of line protection in modular multi-level converterbased multi-terminal DC system, a pilot protection method based on voltage matching factor is proposed. First, the dynamic switching process of flexible DC converter submodule is analyzed, and the expression of DC voltage of converter station considering the influence of alternating current (AC) system is derived. On this basis, the model of DC line voltage considering the influence of AC injection current is built, and the equivalent DC line voltage is calculated according to the voltage model. Then, by constructing the distortion factor which reflects the difference between the equivalent DC line voltage and actual DC line voltage, the protection criterion for the identification of internal and external faults is established. Finally, simulation tests on real time laboratory (RT-LAB) platform verify that the proposed scheme can correctly distinguish between internal and external faults in different fault cases, with fast operation speed and strong immunity to the fault resistance.

No abstract

No abstract

No abstract