Research On Power Quality Detection Method Of Electrified Railway Traction Power Supply System

As an integral part of China's transportation system,railway transportation plays an important role in the daily travel of the public and the economic development of the country.At the same time,in the current environment-friendly society construction advocated by the country,railway transportation also shoulders a very important task.Electrified railways have irreplaceable roles in society,but their loads are nonlinear and fluctuating,which brings about a large number of negative-sequence currents and harmonic currents flowing into the public power system,causing three-phase voltage imbalance and various other power quality problems.These problems have seriously affected the stability and safe operation of the power system and the traction power supply system of electrified railway.Therefore,it is very necessary to obtain more accurate reference commands of negative-sequence current and harmonic current in the railway power supply system,and then to compensate electricity through the active compensation device.In order to solve the above problems,this paper first analyzes the characteristics of negative-sequence current and harmonic current in the traction power supply system of electrified railways,and draws a conclusion that the magnitude of the negative sequence current caused by the traction power supply system of electrified railways is affected not only by the load of the two phases and the phase difference,but also by the type of traction transformer.Secondly,various current detection methods suitable for traction power supply system of electrified railway are analyzed.The current detection methods based on instantaneous reactive power theory and adaptive noise cancellation technology are studied in detail,and a simulation comparison is made.And then a brief introduction to a variety of transient power quality testing methods are provided.Finally,the current detection method based on FBD theory is analyzed.On this basis,a fundamental positive sequence and negative sequence currents detection method based on FBD without PLL is proposed.Only with simple multiplication,it can obtain the fundamental voltage,and thus generate fundamental positive sequence and negative sequence reference voltages.With the reference voltages and currents,the equivalent conductance can be acquired,and then the conductance and reference voltage are used to calculate the fundamental positive sequence and negative sequence currents.The simulation analysis of the proposed current detection method through Simulink shows that the method has simple algorithm and is more real-time and dynamic.Moreover,it can simultaneously detect positive sequence and negative sequence currents in the two-phase currents,which are not affected by grid distortion.This method provides a more accurate current reference command for the dynamic comprehensive compensation of power quality in electrified railway.