Research On Hybrid Filtering Technology Of Locomotive Mixed Running Lines

In the new era,with the continuous development of China’s economy,the demand for rail transportation is increasing,and a large number of electric locomotives are required as a carrier for transportation.However,at present,some of China’s traction networks are in a state of mixed running of AC and DC locomotives,and will be in this state for some time in the future.This mode of operation makes the harmonic content in the traction network drastically increase,and the harmonic spectrum distribution is very extensive.This undoubtedly exacerbates the deterioration of the power quality of the traction and three-phase systems.It is necessary to study a filtering technique that is suitable for the locomotive mix running circuit.For this reason,this article will carry out the research work of the hybrid filter,which is an effective way to improve the power quality of locomotive mixed run lines.The main work is as follows:(1)Aiming at the problems of high voltage levels,wide distribution of harmonic spectrum,and resonance problems in locomotives,a hybrid filtering scheme is proposed in this paper.This scheme effectively combines the advantages of passive filters and active filters.It uses 3 and 5 tuning branches to filter out the main low-order harmonics and has the function of reactive power compensation.The high-pass filter removes higher harmonics having a frequency of 1550Hz-2100 Hz.The active filter filters out the remaining harmonics while suppressing the system resonance.For the problem of unstable voltage on the DC side of the active filter,the voltage stability is maintained by controlling the energy excretion.Focus on the design of high-pass filters,output filters and injection branches and other parameters.(2)In the harmonic detection of the key technology of active filter,the positive sequence fundamental wave extractor algorithm(single-phase system)has certain advantages.However,when there are a large number of low-order harmonics in the system,the detection algorithm cannot simultaneously take into account the faster responsespeed and higher detection accuracy.Therefore,aiming at this defect,this paper proposes an improved algorithm based on the original detection algorithm.By adopting the strategy of extracting low-order harmonics step by step and eliminating them,the contradiction between the fast response speed and the high detection accuracy of the original detection algorithm is effectively solved,and the steady-state error is greatly reduced.Through a lot of simulation analysis,the effectiveness and feasibility of the improved algorithm are verified.(3)In the aspect of active filter control strategy,this paper briefly describes the performance of PI-based controller and sliding-mode controller,and analyzes the advantages and disadvantages of hysteresis control in detail.Aiming at the problems of unstable frequency,high loss and noise in traditional hysteresis control switching,an adaptive constant-frequency hysteresis current tracking control strategy is used in this paper.The active filter can be effectively controlled by changing the fixed frequency of the ring width.Build an overall simulation model in Matlab/Simulink.Through detailed simulation analysis,the results show that the scheme adopted in this paper can effectively solve the problem of power quality caused by harmonics in locomotive mixed running lines.The effect of governance achieved the desired goal.