Research On High-power Super-capacitor Pre-storage Power Station And Its Key Technologies

Improvement and popularization of green public transport technology is one of the main directions of urban ecological environment governance,which has attracted widespread attention in academic circles.Among many types of green public transport,super-capacitor electric vehicles have the characteristics of low environmental pollution,high efficiency and long life,which will become the main types of urban traffic vehicles in the future.In order to improve the competitiveness of super-capacitor electric vehicles and overcome the obstacles caus ed by the low energy density of super-capacitor,it is necessary to establish ground pre-storage power stations along the way.This thesis mainly focuses on the related technical issues of the super-capacitor power pre-storage charging station,aiming at reducing the power impact on the distribution network,optimizing the high-power charging strategy of electric vehicles under specific time windows and improving the level of energy management and safety control of the high-power super-capacitor energy storage system,so as to provide technical reference for the popularize of the super-capacitor vehicles.Firstly,the overall structure and mathematical model of super-capacitor pre-storage power station are studied.The structure of the pre-storage charging station is designed based on the parameter configuration of the super-capacitor tramcar.In order to deeply study the performance of pre-storage power station and realize the simulation and control of the charging station,the mathematical model of pre-storage power station is established.The mathematical model of pre-storage power station includes the model of high frequency PWM rectifier with controllable power factor,the model of isolated three-level DC/DC converter with soft switching technology,the model of interleaved buck/boost converter and high power super-capacitor group model.Among these models,we focus on the high-power super-capacitor group model which includes the voltage balancing system and then simplify the model.An on-line parameter identification method for super-capacitor group based on RLS and RELS double least squares method is proposed to solve the coupling problem between equivalent series internal resistance and the differ ential capacitance of super-capacitor group.Secondly,modular fast voltage balancing system is studied to ensure the safety of super-capacitor energy storage system and extend the service life of super-capacitor group.By reducing the PWM frequency,the balancing current of the multi-winding transformer balancing topology is increased,so that the voltage balancing speed can be improved.In order to apply the multi-winding transformer balancing topology to large-scale energy storage system,a modular multi-winding transformer balancing topology is proposed.The multi-winding transformer balancing topology can not control the voltage of super-capacitor in a differentiated way,then the modular discharge type voltage balancing topology is proposed to realize the voltage differentiated control of the super-capacitors.In order to prolong the service life of super-capacitor group,the voltage balancing strategy based on SOH is studied.In order to reduce the cost of super-capacitor SOH estimation and improve the economy of SOH-based balancing strategy,a method of super-capacitor SOH estimation method which is based on voltage variation is proposed.Then,the high-quality charging technology of the super-capacitor group in the pre-storage power station is studied.The unit power factor rectification with unbalanced power grid is realized by the PWM rectifier.In order to reduce the volume of magnetic devices,charging current ripple and EMI electromagnetic radiation,a soft-switching topology based on active commutation auxiliary circuit is proposed to realize the full load range ZVS soft-switching of the isolated three-level DC/DC converter.In order to ensure the stability of the cascade charging system composed of AC/DC and isolated DC/DC converter,the stability analysis method of the charging equipment was studied.In order to optimize the charging current of super-capacitor group in the energy storage station,a charging strategy based on SOC is proposed,and a SOC estimation method of super-capacitor group based on sliding mode observer is proposed.Finally,the high-power discharge technology of super-capacitor group in the pre-storage power station is studied.The high power discharge topology is composed of interleaved buck/boost converters.The independent control strateg ies with buck mode and boost mode are studied and the switching strategy between the two modes is proposed.In order to solve the stability problem of the converter in buck mode,the damping circuit of the pre-LC filter is designed.In order to solve the problem of current balancing of the input and output current,a democratic hysteresis current balancing method which combines democratic current bal ancing and hysteresis current control is proposed.In order to realize ZVS soft-switching of the buck/boost converter under continuous current,the active clamped ZVS soft-switching technology is studied.An improved active clamped soft-switching topology with the current transfer circuit is proposed which will reduce the current stress of the freewheeling diode,the voltage stress of the main switches and improve the efficiency and reliability of the converter.The key technologies of super-capacitor pre-storage power station are studied comprehensively in this thesis.The research results have theoretical and engineering significance which will provide strong technical support for the rapid development of green public transport.