Dynamic Modeling And Analysis Of Power Quality Of High Speed Railway Traction Power Supply System

The traction loads of high speed railway (HSR) have characteristics such as large traction power, high density traffic, nonlinear, stochastic and so on, which cause serious power quality (PQ) problems such as negative sequence unbalance, harmonics, voltage fluctuations and others to the traction power supply system (TPSS) and the power system. With the development of economy in China, HSRs are in huge demand. In order to meet the demands, China Railway Company adjusts the train timetable in July and December of each year, considering the newly-built railways that put into operation continuously, which increases the traffic density and is bound to inference the PQ of TPSS in some extent. It deserves further study.Firstly, this paper studies the dynamic model method of TPSS traction loads. The force conditions and motion equations of the EMU traction operation are analyzed. The constant speed traction control stratagem is illustrated. According to the conversion relationship among the given EMU traction operating conditions, the flow chart of traction calculation process of EMU is presented. Combined with the demand or feed equations of the EMU networking side and the traction calculation results, the dynamic fundamental model of the EMU is established. And then based on the analysis of the characteristics of the output harmonic current and voltage in different conditions, the dynamic harmonic model of the EMU is established. The simulation results show that the traction calculation algorithm and EMU dynamic load modeling method is feasible and correctness. The flow chart of 24 hours dynamic traction load modeling method of the TPSS is illustrated and each step is described, combined with the train timetable.And then the dynamic mathematical model of the TPSS modeling method is studied. The static mathematical model of the utility system and the traction substation is established respectively. And combined with the dynamic characteristics of the traction loads, the dynamic chain net model of the traction network in any time interval is established. Alternatively, on the basis of the topological structure of TPSS, the dynamic mathematic model of the whole system is established in any time interval.According to the study above, the dynamic power flow calculation method of TPSS is studied, which contains the fundamental and harmonic power flow in any time interval. The flow chart is showed and the detail procedure is set forth. One case of one CRH2A EMU running in the TPSS is simulated. The fundamental current of the EMU and the harmonic currents inject into the three-phase utility system are calculated and compared with the field measurement. The results show that the dynamic modeling and the power flow method is feasible and correct, which can analog the dynamic changes of the electrical accurately during the train operation process.Finally, according to one HSR and its all day train timetable, the 24 hours dynamic changes of some power quality indexes that the TPSS concerns are analyzed, such as negative sequence unbalance, voltage fluctuation, power loss and harmonic distortion. Alternatively, their statistical indexes are assessed, such as 95% probability, maximum, etc. And the simulation results of negative sequence unbalance fits well with the field test data, which verify the algorithm and model once again. The harmonic simulation results show that the background harmonic of the utility system is the main harmonic source of low order, and the EMUs is the main harmonic source of high order. Based on the simulation results, the harmonic resonance of TPSS is further discussed and some relevant advises are put forward to improve the harmonic PQ.