Research On DC-side Harmonic Suppression Method For HVDC Transmission System

The energy resource and load is extremely uneven geographical distribution in our country,the demand for long-distance and high-capacity transmission is more urgent.High voltage direct current（HVDC）transmission system has large transmission capacity,fast response,and do not need to consider the stability of synchronous operation,etc.,it is widely used in our country.HVDC transmission project needs AC/DC conversion according to converter station.The converter station is composed of the power electronic devices,which can produce a large scale of harmonics in the system.For the HVDC system,when the system side has three-phase unbalance,the unbalanced voltage will produce a large number of non-characteristic harmonics including 2^nd harmonic on the DC side of the system through rectifier station,the 2^nd harmonic will be through the inverter station and generate more non-characteristic harmonics,seriously affecting the power quality.The HVDC transmission project of DC filtering system is mainly aiming at each characteristic harmonic,not for the 2^nd harmonic.And due to the unbalanced load,power system always exist three-phase asymmetry phenomenon.In this paper,using Matlab/Simulink simulation software,a HVDC system was built.Simulation tests the suppression effect of practical engineering of DC filter system for the 2ⁿdd harmonic.Simulation results show that the traditional filtering system can suppress the characteristic harmonics,but the suppression effect of the 2^nd non-characteristic harmonics is poor.Aiming at the HVDC DC-side harmonic problems when the system is unbalanced,LC filters can be designed to inhibit the 2^nd harmonic.Based on different schemes for the filter design,compares their performance.Through the analysis of the transfer function of the new filtering system and the frequency response of the filter,the rationality and the stability of the designed filter are proved theoretically.Finally,through establishing the Matlab/Simulink simulation platform of HVDC system,verify the filtering system,which is designed to suppress the 2^nd harmonic in this paper.Results show that the designed filter in this paper has a wide range of output,the demand of DC inductance also can be reduced,and the efficiency of power transmission can be improved,verify the correctness and feasibility of the design method of the filter.