Research On Key Technologies Of Power Capacitor Applied To Flexible DC Transmission Control

The VSC-HVDC technology is a new transmission technology based on voltage source converters,self-shutdown devices and pulse width modulation(PWM)technology.It can adjust the active and reactive power of system independently and quickly,and improve the stability of the system.The DC capacitor in the rectifier and inverter system is an indispensable part of the voltage source converter(VSC).It provides energy buffer for the DC system of the converter system,reduces voltage harmonics on the DC side,and stabilizes the DC voltage of DC transmission system.This article is a key technical analysis of the capacitor in the voltage source converter system.Metallized film capacitors are used in most converter systems today,new materials and new processes are gradually replacing the traditional metallized films,safety film technology has been widely used.The so-called safety film is a regular safety film pattern separated from the insulating material by vapor deposition,but the patterns themselves do not cross each other,but they are connected to each other through fine fuses.When the metal film is locally weak and forms a discharge channel,energy rapidly flows in from all directions,the weak spots around the small module vaporize and quickly self-heal without affecting the normal operation of the entire metal film.In order to further improve the performance of metallized film capacitors,operate at higher field strengths,reduce the loss of fuses and ensure more reliable and safe operation,this article presents a new type of automatic series-parallel high square resistance metallization safety film.According to its progressive energy analysis calculation and the self-healing principle of the safety film,the size of the metallized film under different working requirements and the number of the upper and lower board series and parallel connections are determined,the rated voltage is 2800 V,the rated capacity is 8000?F,the insulation thickness is 7?m,the number of geometrical microelements in series is 2,the number n of parallel-connected modules in the overall length direction is 19608;Analyze the capacity change of capacitance under different fault conditions,and the degree of change in the overall capacitance and the partial pressure of each part;the equivalent series resistance(ESR)of the automatic series-parallel high-barrier metallization safety film was calculated;analysis of its advantages and disadvantages combined with high resistance film;using COMSOL Multiphysics simulation software to calculate the electric field and its distribution of key parts of the common safety membrane and the designed automatic series-parallel high-segment resistance safety membrane.The performance of the safety membrane designed in this paper is better than that of the ordinary safety membrane,and is further optimized through simulation calculation.The new metallized safety film designed in this paper can work under higher field strength,and there is no loss of the fuse part of the traditional safety film.