Harmonic Characteristics and Negative Sequence Analysis of Regenerative Braking for High-speed Railway

Background: The traction power supply system (TPSS) of railway mainly focuses on power quality analysis. In the study of harmonic and negative order currents, about 80% of the literature analysis are not specific enough there is a lack of completeness in the simulation system. Objective: Analyze the influence of harmonic and negative current sequences of TPSS on the system circuit, and realize intelligent recognition for different working conditions. Methods: The converter is designed based on the transient direct current control technology and the harmonic model of grid-side regenerative braking is established. According to the parameters of CRH2 (CRH380AL) locomotive, the EMU model is built and run in the TPSS for joint simulation. The availability of the model is verified by combining the harmonic content and voltage level. Then, the distribution of negative sequence current under the no-load, traction and regenerative braking conditions of the system is analyzed in detail, and the negative sequence characteristic waveform under various conditions is obtained, so as to obtain the variation law of negative sequence current under different conditions. Results: Under the regenerative braking condition, the current harmonic distortion is much higher than that under the traction condition. From the analysis of voltage and current phase, the power factor of regenerative braking is also small. In the negative sequence analysis, the tip negative sequence current impact phenomenon occurs mostly during the traction operation of the train, while the current impact effect is weakened during regenerative braking, but the amplitude of the negative sequence fluctuation shows an increasing trend. Conclusion: The energy generated by regenerative braking will be utilized by the locomotive under traction, and these bad electric energy forms will have extremely adverse effects on the process of high-speed train receiving and changing current. These negative sequence analysis results can be used to identify and classify different working conditions and divide and conquer energy compensation actions to achieve energy saving and consumption reduction.