Harmonic Effect Of High-speed Railway Traction Power Supply System On Utility Grid

The rapid development of high-speed railway greatly meets the needs of production and livelihood, which also accords with the practical requirements of the energy reduction and environment protection policy in our country. Due to the traction trains containing a large number of nonlinear elements and obtaining power as a single phase load from the grid, the harmonic and unbalance generated will cause adverse effects on the safe and stable operation of traction power supply system and power grid. Therefore, it is of important significance to carry out research for the traction power supply system and its impact on power quality.Based on the structure and working principle of high-speed railway traction power supply system, this paper mainly analyzes the fundamental and harmonic power flow algorithm, as well as the characteristics of harmonic sources considering curve additional resistance. On this basis, a traction supply system with trains and network coupled is built so as to analyze the grid side harmonic voltage and current situation in different operating conditions. Besides,this paper estimates whether low-order harmonics exceed the allowable value for Qixian and Jiexiu east station of Datong-Xi’an High Speed Railway.The advantages and disadvantages are compared between power injectionNR method and current injection NR method since the former is more strict to the initial value. It is clear that the current injection NR has a better convergence characteristics. Then the improved current injection NR algorithm considering vehicle coupled with traction network is proposed, which proved to be feasible through some examples. In terms of harmonic power flow algorithm,optimization of network-locomotive coupling factor on admittance matrix of traction network under single line model is executed. Then a coupling based algorithm is proposed. Harmonic power is superimposed to the fundamental power flow in the iterative process. And this algorithm is proved to be effective.Due to the effect of actual road conditions on EMU in the course of driving,This paper establishes a traction drive system considering curve additional resistance to make the simulation more practical. Drive system torque characteristics are analyzed when the EMU running in single plane curve, three S-shaped curve and curved ramp road. And the characteristics of harmonic source in curve road conditions are studied. It turns out that the electromagnetic and load torque increased and harmonic distortion aggravated in traction condition with the additional resistance of curve included. In regenerative braking conditions, fundamental current of grid connection point decreased and harmonic distortion is more serious than traction conditions.In addition, the influence of harmonic in traction power supply system on power grid is analyzed via MATLAB and RTDS. Based on MATLAB /SIMULINK, the paper builds all parallel AT traction power supply system andanalyzes the harmonic voltage and current characteristics with a single power supply arm. Besides, harmonic information under 63 are extracted and simulated with discreter fourier harmonic analysis module in RTDS/RSCAD.And this paper analyzes the harmonic characteristics of the traction power supply system under B phase grounding fault and CA phase to phase short problems The results show that two types of faults lead to a train load terminal voltage decreases. Severe harmonic distortion will appear in the starting and ending. During the fault period, the overall the harmonic current increased and the even harmonics increase significantly. In both fault types, some harmonics show the opposite changes, that is, the fault harmonic current is less than the state value of the fault. It has a bad influence on the stable operation of traction system. Which provides a theoretical basis for the study of the harmonic characteristics of high speed railway system.Take Qixian East-Jiexiu east traction power supply system of Datong-Xi’an railway example. This paper estimates whether the harmonic index exceed the standard through low-order harmonics data of single train under rated power. It is verified that the method is effective and has practical significance to the actual system operation and maintenance.