Development Of Supercapacitor Energy Storage Converter For Regeneration Energy Of Subway

Because the distance between the subway stations is relatively close,the train starts and stops frequently.When the train stops,it can transform the kinetic energy of the train into electric energy through regenerative braking.If the regeneration energy can not be absorbed by other vehicles on the line,it will raise the voltage of the traction network,and threat the train operation safety.In the early stage,regenerative braking energy was converted into heat energy to consume through on-board braking resistors or ground braking resistors.How to make full use of regenerative braking energy has become a research hotspot in recent years.Compare with currently used subway regenerative energy feed device,the regenerative braking energy can also be stored by the supercapacitor,and returned to the traction network when the train is started.This method can not only make full use of the regenerative energy,but also compensate the voltage landing of the traction network and reduce the peak power of the medium voltage AC network.With the increase of the energy density of the supercapacitor and the decrease of the price,the strategy of using supercapacitor to solve the problem of regenerative energy has been paid more and more attention.In this paper,a bidirectional DC/DC converter for Metro supercapacitor energy storage device is developed based on the entrusted project of a company.The main work of this paper is as follows:Firstly,for the needs of subway regenerative braking applications,the half-bridge,multi-phase interleaved half-bridges,the input side cascading multi-phase interleaved half-bridge,the three-level with the input and output sharing the ground and the three-level with the input and output without sharing the ground bidirectional DC/DC topology are analyzed.It is concluded that the three-level with the input and output without sharing the ground bidirectional DC/DC topology can not only improve the equivalent switching frequency,reduce the inductance and noise,but also have the characteristics of convenient charging,which is more suitable for practical use.Then the working principle of the topology is analyzed.Secondly,According to the selected topology,the reason of the unbalanced voltage in the high voltage side is analyzed.The complementary modulation method is selected and the voltage balance control strategy based on the voltage difference control is proposed.The current controller structure based on the voltage feedforward is designed,analysis shows that the voltage feedforward can improve the dynamic response speed of the converter.A three stage charging strategy based on dynamic threshold is designed after analyzing the energy characteristics of the Metro regenerative braking.All the above control methods are verified by simulation.Thirdly,according to the technical requirements,the parameters calculation and selection of the power devices,inductors and partial voltage capacitors in the main circuit are completed,and the supercapacitor group is also designed.The dual core control board of ARM+FPGA and signal conditioning baseboard are designed for the demand of the subway,and the communication function of ARM and PSCADA,ARM and touch screen,and the function of remote firmware update(including ARM program and FPGA program)based on Ethernet are implemented.The HDL Coder toolbox in MATLAB is used to generate the Verilog code corresponding to all the core algorithms in FPGA,which improves the development efficiency and the reliability of the code.Finally,a simulation platform including main circuit,control circuit,supercapacitor and debug computer is built in the laboratory.The experimental results show that the ARM+FPGA control board can control the converter work steadily and reliably,and realize the remote Ethernet communication function.The current control algorithm can realize the constant current charge,discharge,and stop charging?discharging at the maximum voltage and the lowest voltage when the voltage reaches the overcapacity;the energy management strategy can control the charging and discharging current of the converter according to different bus voltages.In this paper,the hardware and software parts of the energy storage device are designed based on the project of the regenerated energy supercapacitor power storage converter entrusted by the enterprise.The core algorithm of bidirectional current control and voltage sharing control is preliminarily verified in the laboratory,it also verifies the Ethernet based remote monitoring and firmware update function.The system plan and control algorithm still need further verification on the engineering prototype.