Research On Control Strategy Of Auxiliary Four Quadrant Converter For Electric Locomotive With Active Filtering Function

With the advantages of strong transport capacity,being environmental-friendly,safety and reliability,electrified railway plays an important role in the national economic and social development of our country.With the large number of electric locomotives put into operation,the locomotive will inject harmonic currents of specific frequencies into the traction network during operation.When these harmonic currents have the same frequency as the characteristic frequencies of the traction network,the vehicle-network coupling resonance will occur.If the resonance voltage is too high,it will cause resonance accidents such as locomotive tripping protection and equipment burning along the line.In recent years,there have been many vehicle-network coupling resonance accidents in China.Therefore,it is very important to effectively suppress vehicle-network coupling resonance for the safe and stable operation of electrified railway.In order to suppress the vehicle-network coupling resonance,an active filter control method based on SiC for locomotive auxiliary four-quadrant converter(4QC)is proposed in this paper.In this scheme,no additional power electronic devices are needed.At the same time,SiC devices are applied to on-board auxiliary converters,which is beneficial to the lightweight of Locomotives.Firstly,generation mechanism of electric locomotive harmonics and the vehicle-network coupling resonance mechanism are analyzed.In order to realize the rectification function of unit power factor and active filter control of auxiliary four-quadrant converter,the influence of inductance and switching frequency on harmonic current compensation effect of network side is analyzed,and the selection method of inductance parameter threshold is proposed.Secondly,an active filter resonance suppression method for auxiliary four-quadrant converter is proposed.In view of the complex background harmonics and large fluctuations of electrified railway,the accuracy and real-time performance of the adaptive detection method and sliding window discrete Fourier analysis method are compared and analyzed,and the latter method is proposed to extract harmonic instructions.Aiming at the broad frequency bandwidth characteristic of harmonic current instruction,a parallel multiple proportional resonance(M-PR)controller is adopted to track the harmonic current without error,so as to restrain the harmonic current injected into the traction network.The validity of the proposed active filter method to suppress harmonic current and harmonic voltage is verified by simulation with MATLAB/simulink.Thirdly,the stability of active filter control is analyzed.The proposed control strategy is discretized by using pre-distortion bilinear transformation method.The stability of the system in high frequency compensation and the influence of parameters and number of parallel resonant controllers on the stability are analyzed in the discrete domain.The validity of the simulation and hardware-in-the-loop experiment is validated by using MATLAB/simulink simulation and RT-LAB hardware-in-the-loop platform.Finally,a 15 kW vehicle-network coupled resonance experimental prototype is built to simulate the coupled resonance system of electric locomotive and traction network.The topology and parameter design of the experimental prototype are analyzed in detail.The IGBT device is used in the traction four-quadrant converter and the SiC device with 10 kHz switching frequency is used in the auxiliary four-quadrant converter.The experiments of harmonic detection,harmonic suppression,resonance suppression and stability analysis are completed by using the experimental prototype,and the effectiveness of the proposed active filter resonance suppression method is verified.