Key Technologies Of Reflux Safety In DC Traction Power Systems

DC traction power system is usually used in urban rail transit lines to provide power for the train.Abnormal rise of the reflux parameters including rail potential and stray current exists in dynamic operation of the system,which will cause serious damage to the safety operation of the system and the underground pipelines.Currently,rapid development of urban rail transit lines has achieved in China,and there is an important significance to ensure the operation safety of DC traction power systems.In this paper,research of reflux safety in DC traction power systems have been carried out,including the simulation methods of reflux safety parameters,mechanism of abnormal rise of the reflux safety parameters and control methods in the optimal operation of the system.The characteristics of DC traction power systems and the reflux safety parameters are studied in this paper.The steady-state characteristic of rectifier units is analyzed,and the output characteristic curve with multiple polylines is obtained.The characteristic of hybrid parameters in the reflux system including distributed parameters and lumped parameters is elaborated,and the operation characteristics of the control equipment for reflux safety parameters are analyzed.The models of train movement calculation and regenerative braking energy absorption device are established,and the load variation and output characteristics are studied.The distribution model of reflux safety parameters with single power supply section is established,and the distribution of reflux safety parameters is analyzed theoretically.Combining with the abnormal rise of reflux safety parameters in practical operation,the issue is clarified that existing models and theories cannot effectively simulate and control the reflux safety parameters.A simulation method of reflux safety parameters with complex operation of the system is proposed in this paper.Fast and accurate simulations of reflux safety parameters are realized.The method for the equivalence and parameter modification of reflux system with hybrid parameters is presented,which will ensure the exact equivalence of the reflux system.A unified chain model of DC traction power supply system is established and the power flow calculation with complex operation of the system is studied.The calculation model of reflux safety parameters is proposed to realize the calculation of reflux safety parameters.Based on the alternating iteration method,the AC/DC power flow calculation method is studied.Results of the simulations and example verification show that the simulation methods can realize the fast calculation of the reflux safety parameters in complex operation of the system.At the same time,power distribution over sections widely exists when multiple trains run in multiple sections.Studies are carried out on the mechanism of abnormal reflux safety parameters in this paper.Association model of the reflux safety parameters and over sections feeding is established in this paper to analyze the effects of over sections feeding on reflux safety parameters.Power flow tracing method in DC traction power systems is proposed,and the power distribution when multiple trains run in multiple sections can be realized.A decomposition method of the reflux safety parameters is presented to evaluate the impact of current distribution component on the reflux safety parameters.Based on the parameters of actual line,effect of power distribution on the abnormal rise of the reflux safety parameters is simulated and analyzed,the mechanism of abnormal reflux safety parameters is expounded.Simulations on the effects of train coincidence and trigger voltage of regenerative energy absorbing device on reflux safety parameters are carried out.Field tests results show that the power distribution over sections can lead to abnormal rise of the reflux safety parameters.Researches on the control methods of reflux safety parameters with regenerative energy management are carried out in this paper.Relationship between the energy saving operation process and reflux safety parameters are expounded.Different calculation methods of regenerative braking energy distribution are analyzed.The optimized objective and model of regenerative energy management are proposed to realize the optimization of the reflux safety and energy saving.An improved chaotic particle swarm optimization algorithm for regenerative energy management optimization is proposed.Idea of chaos algorithm and dynamic inertia weight is incorporated into the particle swarm optimization algorithm to avoid premature convergence and improve the convergence speed.Simulation results show that the regenerative energy management can realize the reflux safety and reduce the power loss.Studies on the reflux safety parameters and energy saving operation in energy-fed traction power system are carried out in this paper.Model of the bidirectional converter for power flow calculation is established.In this paper,a control scheme of reflux safety and energy saving operation is proposed based on bidirectional converter.Simulation results show that DC traction power systems with bidirectional converter can realize the automatic division of power supply.In this way,the reflux safety parameters and the power loss of the system can be reduced.Finally,a three level bidirectional converter of 2MW in DC traction power systems is designed,and the characteristics of bidirectional converter are tested.