Research On High Frequency Harmonic Suppression Of Traction System Based On Magnetic Integrated LCL Filter

The high frequency harmonics of the traction network are mainly generated by the frequent switching of the converter drive converter switch.This harmonic is also the main excitation source for the harmonic resonance of the traction network.To reduce the occurrence of harmonic resonance,it is necessary to suppress or eliminate the highorder harmonic current injected into the traction network.China high-speed railway traction drive system generally uses the traction transformer leakage inductance as the input filter of the grid-side converter,so that the high-order harmonic content of the grid side current is higher.Due to the restrictions on the installation space and weight of the high-speed railway body,if the traction transformer leakage inductance value is increased to reduce the high-order harmonic content of the grid side current,the volume and weight of the transformer will increase.Therefore,from the research of a highorder harmonic suppression scheme suitable for limited installation space,this paper proposes a scheme to configure a magnetic integrated LCL filter on the front end of the rid-side converter.Firstly,the topology of the magnetic integrated LCL filter at the front end of the grid-side converter is introduced.The magnetic integrated LCL filter consists of three parts,one inductor uses the traction transformer leakage inductance,and the other inductor is integrated into the traction transformer through magnetic integration technology,and then connect a capacitor in parallel.And the transfer function and filtering characteristics of the rectifier main circuit based on LCL filter and large filter are analyzed and compared.Then according to the design principle of LCL filter parameters and the influence of each parameter on the filtering effect,the values of each parameter of the LCL filter are designed.Secondly,for the problem that an inductor is integrated into the traction transformer,the decoupling principle of the transformer winding and other integrated filter windings is analyzed,and the calculation formula of the inductance value and the coupling degree of the transformer winding is derived.For the problem that the leakage inductance of traction transformer is used for the other inductor,the calculation method of the traction transformer leakage inductance value is given.System simulation model established based on the MAXWELL/Ansoft and MATLAB/Simulink,and the two inductance values and coupling degree are calculated to verify the correctness of the proposed decoupling scheme and calculation method.Then,the basic passive damping and active damping control schemes are analyzed for the inherent resonance peak problem of LCL filter.For the shortcomings of the basic damping schemes,a control strategy for estimating the capacitive current feedback is proposed in the original transient direct current control.Based on the magnetic field circuit coupling simulation method,the effectiveness of the proposed control strategy and high frequency harmonic suppression is verified.Finally,the integrated filter winding inductance value,leakage inductance value and winding coupling degree of 10 kVA integrated filter winding single-phase transformer prototype are tested to verify the correctness of the proposed decoupling scheme and inductance values calculation methods.Comparing the area and volume of the integrated filter inductor transformer with the traditional transformer configuration of the discrete inductors,it is verified that the magnetic integrated LCL filter can reduce the size and space of the device.The system experimental platform was built to verify the high-order harmonic suppression effect of the magnetic integrated LCL filter in the traction system.