Research On Dc Bus Voltage Resonance Mechanism And Incoming Line Protection Optimization For Metro Substation

Urban subway transportation is an excellent solution to alleviate urban traffic pressure,construct new development patterns,and promote green travel.It is also the best business card to enhance the city’s brand image and demonstrate comprehensive strength.The subway adopts electric traction,and its safe operation depends on the stability and reliability of the power supply system.With the increase of traffic density and the increase of new energy grid connection rate,the electrical characteristics of the subway power supply system have undergone significant changes.Not only do special loads such as line faults often occur on the traction side,but also the DC bus voltage begins to exhibit significant resonance phenomenon.Therefore,it is necessary to start with the construction of subway power supply system circuits,explore the mechanism of DC bus voltage resonance,and then develop a new type of incoming line protection method that can efficiently avoid short-term reverse current.Firstly,the simulation verifies the cause of DC bus voltage resonance.On the basis of briefly explaining the topology structure,main wiring scheme,and operation status of the subway power supply system,the paper analyzes the configuration and working principle of DC bus and incoming line protection,and builds a semi physical simulation model of the subway power supply system based on the RT-plus intelligent digital simulation platform by calculating and configuring simulation parameters;By adjusting the configuration parameters of the simulation model,it was verified that the external cause of DC bus voltage resonance is the oscillation of the urban power grid,while the internal cause is the unstable conditions of the subway power supply system.Secondly,construct a nonlinear dynamic circuit model and identify the structural factors of DC bus oscillation.From the perspective of nonlinear dynamics,an in-depth exploration was conducted on the causes of resonance in the system.Therefore,a mathematical model of the third-order nonlinear non-autonomous state equation of the AC side rectifier transformer circuit was established.By adding a time dimension,the third-order non-autonomous system was transformed into a fourth-order autonomous system.Numerical analysis was used to obtain the rich dynamic behavior of the system under different excitations,and the three-dimensional phase diagram,phase plane diagram A more in-depth analysis was conducted on the Poincar é mapping and bifurcation diagrams;Compare the chaotic waveform obtained from simulation with the on-site measured oscillation voltage after 24 pulse rectification,and verify that its waveform characteristics are basically consistent.Finally,a DC bus incoming short circuit identification algorithm based on the combination of variational modal decomposition,sample entropy,and TOPSIS is proposed.A subway incoming current fault diagnosis algorithm based on variational mode decomposition,sample entropy,and TOPSIS algorithm has been constructed;Using VMD to decompose the original current and determining the optimal number of modal components through the Cal evaluation index;By using the sample entropy kurtosis correlation coefficient fault diagnosis model,the weight analysis is performed on the optimal modal components obtained,and then the TOPSIS method is used to evaluate the relative fitting progress of the VMD feature modal components,completing the identification of the current state.The experimental results show that the protection algorithm based on variational mode decomposition,sample entropy,and TOPSIS algorithm has strong recognition ability and high sensitivity,and can reliably identify atypical currents in subway DC incoming lines,providing backup protection for subway DC incoming lines.