| Along with the development of the electrified China railway,it has become a trend to construct the hub traction substation(HTS)that powers many electrified railways of different levels simultaneously.Compared to conventional traction substations,the HTS faces more severe harmonic issues.It mainly manifested in the following three aspects.1)Primarily,there are more electric locomotives,which have different traction drive system and conditions,operating in the HTS.It enriched the harmonic spectrums.2)The quantity of the electric locomotives that simultaneously run in the power supply section of the HTS is more,which would cause more complex harmonics interaction in the HTS.3)The length of power supply lines connected to the same bus in the HTS has dramatically increased.It causes a larger distributed capacitance and inductance.Consequently,the frequency impedance characteristic becomes more complex,and it may cause more severe resonance overvoltage in the HTS.Therefore,this paper analyzed the harmonic characteristics of electrical locomotive with different traction drive systems and the harmonic modeling method.Then,it studied the harmonic modeling of the HTS and the harmonic power flow calculation.Ultimately,it discussed the influence of different factors on the system harmonics and studied related harmonic filtering schemes.The specific research contents are as follows:(1)It analyzed the harmonic characteristics of the electrical locomotives with different traction drive systems,and it established the related harmonic model.Primarily,it analyzed the harmonic output mechanism of AC-DC and AC-DC-AC electric locomotives.Then,it analyzed the typical harmonic characteristics of the CRH2 A EMU with the filed measured harmonic voltage and harmonic current at the pantograph.The characteristics mainly include the amplitude-frequency characteristics,phase-frequency characteristics,and interactive characteristics under different operation conditions.Then,it established the harmonic model of the EMU with decoupled harmonic Norton equivalent modeling method.Moreover,it solved the parameters with a robust complex linear regression method.Case studies verified the accuracy of the proposed method.(2)It studied the harmonic modeling method and power flow calculation method of the HTS.Firstly,it established the harmonic model of the primary electrical cells in the HTS according to their operating mechanism.The electrical cells contain the utility power system,the traction transformers,the feeder cables,and the overhead catenary system with multiple feeders.In which,the background harmonics were considered to model the utility power system.Moreover,it established the harmonic model of the HTS with the topology of the HST.On this basis,it studied the harmonic power flows with the harmonic model of the traction load.Finally,it conducted some case studies,and the results verified the effectiveness of the studied modeling method and the harmonic power flow calculation method.(3)It studied the influence of essential factors,including the operating conditions,locomotive types,and background harmonics in the utility system,on the harmonic of the HST.Moreover,it summarized the harmonic characteristics of the HST.The simulation results show that the harmonic issues of the HTS are mainly the harmonic amplification problem caused by the complicated structure of the power supply lines and the characteristic harmonic superposition and attenuation problems of different types of electric locomotives.(4)It designed a harmonic suppression scheme with the passive filters to solve the harmonic issues in the HTS.Moreover,it estimated the effection of the proposed scheme with filter efficiency.The research results indicate that the designed the harmonic suppression scheme based on the combination of C-type filter,and single-tuned filter can effectively suppress the harmonic issues of the hub traction substation.Finally,the paper summarized the research contents and prospected of the following research plan. |
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