Study On Hybrid Wideband-harmonics Filter For Electrified Railway

In recent years,the number of high-speed EMUs and AC-DC-AC locomotives put into operation in China has increased significantly.Compared with the traditional AC-DC locomotive,the low-frequency harmonics caused by the AC-DC-AC locomotive are reduced,but the main harmonic spectrum of the output becomes wider and the high-frequency harmonic content increases.The cross-straight locomotive represented by the Shaoshan series is still widely used in China’s electrified railways.The characteristic harmonics of this series of locomotive are mainly concentrated in the low frequency band.At present,AC-DC and AC-DC-AC locomotives are running on the same line.Therefore,low-frequency and high-frequency coexisting wideband harmonics are injected into the traction network,which may easily cause harmonic resonance accidents.Harmonic resonance accidents will affect the safety of electrified railway transportation.This paper is devoted to researching a hybrid wideband-harmonics filter for managing wideband harmonics,which has certain guiding significance for the safe operation of electrified railways.This paper compares and analyzes the commonly used filter schemes,and proposes a new type of hybrid wideband-harmonics filter,which consists of a passive part and an active part.The passive part and the active part are used to compensate the high-frequency harmonics and low-frequency harmonics,respectively.By adding a fundamental resonance circuit at the front end of the active part to prevent the fundamental current from passing through,thereby reducing the fundamental voltage of the active part.Meanwhile,the 3rd and5 th harmonic resonance circuits are set to prevent the compensation currents from the active part from being shunted,and to ensure the compensation efficiency of the active part.The filtering principle of the hybrid wideband-harmonics filter was analyzed,and it is pointed out that the active part of the hybrid wideband-harmonics filter is equivalent to a harmonic impedance connected in series with the system side to improve the filtering performance of the passive part.In addition,the characteristics of the hybrid wideband-harmonics filter were also analyzed.Then the parameter optimization and control strategy of the hybrid wideband-harmonics filter in the traction power supply system are studied.Taking the total harmonic distortion rate of the traction power supply system as the optimization target,the parameters of the hybrid wideband-harmonics filter installed on the ground traction substation are optimized.Meanwhile,the single-phase arbitrary-order harmonic current detection algorithm and triangular carrier current control used in this paper were introduced.Finally,a simulation model of the traction power supply system and the hybrid wideband-harmonics filter was built in Matlab/Simulink,and the blocking function of the hybrid wideband-harmonics filter to the fundamental,3rd,and 5th harmonic currents was verified through simulation,which also verified its resistance to low-order harmonics.Low-frequency and high-frequency coexisting wideband harmonics can be effectively compensated,and the resonance of the traction network can be suppressed.And verify that the active part does not bear the fundamental voltage and mainly withstand the low-harmonic voltage.A low-power experimental platform based on FPGA is built,and the feasibility and effectiveness of the hybrid wideband-harmonics filter are further verified through experiments.