Simulation Study On High-Order Harmonic Resonance In Traction Power Supply System Of High-Speed Railway

With the wide application of AC-DC-AC multiple units in electric railway, harmonic characteristic in the traction power supply system has been changed. Not only the low-order harmonics, for example, third-order, fifth-order and seventh-order harmonic were included in this system, but also a lot of high-order harmonic were contained. Although the content rate of these high-order harmonics is very low, the possibility of harmonic resonance in the system will greatly increase. When harmonic resonance occurred in the system, overvoltage and overcurrent will produce, which can endanger equipment insulation of traction substation and train and influence the system safety operation. Severe amplification of harmonic current in traction substation and section post that caused by system resonance has lead to the bus voltage rising. The similar case had happened in some local engineers.Traction network means a single-phase power transmission line with multi-conductor. Its impedance-frequency characteristic can be ignored in the condition of power frequency. When there are high-order harmonics in the system, this characteristic must be considered. The impedance-frequency characteristic, amplification of harmonic current of the traction network and suppression method of harmonic current amplification have not been fully researched. In the aspect of simulation study on the traction power supply system, the existing simulation model has been improved. To solve this problem, some researches have been done in the following parts in the paper.In order to illustrate the impedance-frequency characteristic of power transmission line, the state variables method is applied in the impedance-frequency characteristic analysis based on the reasonable equivalent circuit of power transmission line. This characteristic indicated that the possibility of harmonic resonance occurrence will greatly increase when the system has lots of harmonic components, so the impedance-frequency characteristic of power transmission line must be considered in this case.The unit length impedance and admittance of the traction network are obtained by the equivalent reduction method of power transmission line with multi-conductor. Based on the travelling wave theory of transmission line, the distributed parameter model of the traction network is built and the factors those influence amplification of harmonic current in traction network are discussed in detail. The harmonic orders those may cause harmonic current amplify and their corresponding magnification are obtained. In order to show the influence of harmonic current amplification in the practical system, this paper analyzes the influence degree of the feeder current in traction substation based on the harmonic current characteristic in the traction network side of the CRH2 multiple units when it run under the traction condition. Finally, the suppression methods of harmonic current amplification are analyzed and compared, the suppressive effect and the rationality of second-order damped and series tuning filtering device are discussed respectively.In order to provide a simulation and verification platform, this paper built the simulation model of the traction power supply system by PSCAD/EMTDC. The electrical characteristic and catenary voltage level of the traction network are studied based on this simulation model. Finally the phenomenon of harmonic current amplification and its suppressive effect are simulated and analyzed, and the result of simulation validates the rationality of suppression method.