Research On Regenerative Braking Energy Storage Strategy Of Electrified Railway Based On Hybrid Energy Storage

With the continuous progress of power electronic technology and control technology,the electrified railway represented by high-speed and heavy load train has been developed rapidly,and the running speed and departure density of trains have also been improved significantly.In the process of braking,the regenerative braking is used by the train preferentially,which will generate a large amount of regenerative braking energy.Since this part of the energy contains a lot of harmonics and negative sequence components,the electric sector take the punitive charges for this part of energy,which increases the operation cost of the railway sector.Therefore,an electrified railway regenerative braking energy storage scheme that combines Railway Power Conditioner(RPC)and hybrid energy storage devices is proposed in this thesis,and the control strategy of the scheme and the capacity allocation problem of hybrid energy storage devices is mainly researched on.It is of great significance to improve the utilization rate of electrified railway regenerative braking energy and reduce the operation cost of the railway sector.Firstly,the regenerative braking technology of electric locomotive is studied,and the source of regenerative braking energy is analyzed.Aiming at three kinds of regenerative braking energy recovery and utilization technologies of energy consumption type,energy feedback type and energy storage type,the advantages and disadvantages of the working principle,technical feasibility and energy utilization rate are compared and analyzed respectively.According to the comparative analysis results,the energy storage scheme is selected and the topological structure of regenerative braking energy storage system of electrified railway is put forward.The system is mainly composed of traction power supply system,RPC and hybrid energy storage device.This thesis focuses on the analysis of the working principle of RPC.On the basis of building RPC equivalent mathematical model,the compensation principle of RPC for negative sequence current is studied.Then the topology of several bidirectional DC-DC converters is analyzed,and the working principle of the bidirectional DC-DC converter of Buck / boost circuit is studied in detail.Secondly,the energy transmission characteristics of the traction substation both sides are analyzed according to the energy flow situation of the feeder section.For the proposed energy storage RPC,the compensation principle of negative sequence and harmonic current is analyzed,and the control strategy is further studied based on the compensation principle.For the hybrid energy storage device,the low-pass filtering method is used to divide the reference power to be stored into high and low frequency to be distributed to the super capacitor and the battery respectively,so as to obtain the stored reference current,which is used as the signal to generate PWM wave to control the bidirectional DC-DC converter.The simulation model is built in Simulink to verify the control strategy.It is found that the proposed control strategy not only can store the regenerative braking energy effectively,but also can significantly improve the power quality problems caused by negative sequence and harmonic current.Finally,in the aspect of hybrid energy storage devices capacity optimization allocation,in order to achieve the unity of economy and capacity allocation,a capacity optimal allocation model for economic cost evaluation of energy storage device is established.The regenerative braking power that need to be stored is decomposed into a series of modal components from low frequency to high frequency by using the variational mode decomposition algorithm.The reasonable frequency dividing point is selected by calculating the mutual information entropy between the modal components,and the power is reconstructed into low frequency and high frequency as the storage power of the battery and super capacitor respectively,so as to obtain the economic cost of the capacity allocation model.The simulation results show that the proposed capacity allocation scheme is more economical than other capacity allocation schemes.