Research On Several Issues In The DC Side Harmonic Calculation

With the fast development of the high voltage direct current programs in China,the corresponding tasks on design are becoming heavier,and the corresponding demands on all different kinds of details are becoming stricter.As an important procedure during the design of direct current side filters,calculation of harmonics is playing an essential role during the direct current design program.This thesis makes researches on the detailed implementation process and the improvement scheme of some existing methods,the main contents are organized as follow:(1)The detailed implementation process of three-pulse formula algorithm is analyzed.Using the boundary condition of reactance dx,commutation angle ??direct voltage Ud and direct current Id,the proper combination of these variables can be found.Then the specific calculation method of three pulse harmonic voltages is elaborated.(2)The improvement direction for the piecewise algorithm is given.The drawback of the previous piecewise algorithm is talked about,focusing on lack of consideration on the negative sequence voltage during the calculation of commutation angle.A new circuit model is then raised in order to improve the formula of commutation angle.And then the calculation method of harmonics using these commutation angels is put forward.(3)The statistical methods for the improved piecewise algorithm are put forward based on the introduction of random parameters.Two ways of statistics are mentioned:the biggest incompatible combination method and the expected distribution method.Their statistical results are compared to the matured engineering program and their accuracy is discussed.(4)The calculation results of three pulse formula algorithm and the improved piecewise algorithm are compared.Based on the same set of parameters,the harmonic results of three pulse algorithm and the improved piecewise algorithm are compared and their pros and cons are discussed.Then the method of how to combine the two results is put forward,in order to make the most accurate estimation of harmonics.