Research On Power Quality And Braking Energy Recovery Control System Of Electrified Railway

On account of the unique power supply structure of traction power supply system(TPSS)and the nonlinear and fluctuating characteristics of locomotive load,the TPSS has many problems,such as low power factor,negative sequence and high harmonic content,which seriously affect the safe and reliable operation of locomotives and the utility grid.For these problems,the railway power conditioner(RPC)is undoubtedly the ideal solution.However,due to the need to use two single-phase multi-winding coupling step-down transformers,there are high loss,large covers space.In addition,the compensation capacity of RPC is too large,resulting in the overall cost of the device is too high,which lim its its large-scale engineering promotion and application.Therefore,it is particularly urgent and necessary to study the power quality compensation system with cost advantage,high reliability and high performance.Additionally,railways are big consumer of electricity,it has plenty of room to improve power use efficiency,reduce the electricity cost,etc.Therefore,to carry out the research work of regenerative braking energy recovery on the sustainable development of electrified railway has the very profound significance.Aiming at the problems of power quality management and regenerative braking energy recovery,this paper proposed corresponding solutions,and makes in-depth research and analysis on the circuit topology structure,compensation principle,controller design,model simulation,hardware experiment and engineering application.The research content of this paper is mainly reflected in the following aspects:(1)Based on a large number of field measured waveforms and data from three typical traction substations,and combined with method of mathematical statistics,the basic characteristics and distributio n rules of negative sequence current/voltage,power factor,feeder voltage fluctuation,and regenerative braking energy feedback of the TPSS are analyzed in detail.These contents provide important research materials and reference basis for the research of power quality control and regenerative braking energy recovery.(2)A high power hybrid electrified railway compensation system based on YNVD connected balance transformer is proposed.The compensation device is composed of passive power filter and active compensation device.The former is used to filter out the main harmonic current and compensate the reactive power according to the load,while the latter is used to suppress the negative sequence and compensate the remaining small amount of reactive power and harmonics.By combining the advantages of passive compensation and active compensation,the system greatly reduces the total cost of the whole set of devices under the premise of obtaining the same power quality control effect.By directly integrating the active compensation device into the tap of the secondary side winding of the main transformer,the system integration is improved.The capacity configuration and reactive power distribution method of passive devices are given,and the principle of negative sequence,reactive power and harmonic compensation and current detection algorithm of active compensation are analyzed in detail.On the basis of constructing the discrete mathematical model of the system,this paper applies the deadbeat repeat control algorithm to the current loop control of the converter,and gives the detailed design process of the control parameters.Finally,simulation and experiment al results verify the feasibility of the proposed topology and deadbeat repeat control strategy.(3)A cophase power supply system for electrified railway is studied,which is composed of a YNVD connected balanced transformer and an integrated power flow controller(IPFC).The system can save a single phase step-down transformer by taking full advantage of the secondary side triangular winding of YNVD connected balance transformer with flexible and adjustable tap.Therefore,the cost and cover space of the device can be reduced.The whole structure of the cophase power supply system is introduced.On the basis of establishing the equivalent circuit model of the system,the compensation principle of the cophase power supply system is analyzed in detail.In order to reduce the design difficulty of the controller and the computational burden of the control a lgorithm,a current controller based on a generalized integral iterative control algorithm is proposed in this paper to realize the no-error adjustment of the IPFC.Finally,the correctness of the proposed topology and control strategy is verified by establishing software simulation model and scale-down experimental prototype.(4)A supercapacitor based energy storage system integrated railway power conditioner(SCESS-RPC)is proposed in this paper.The system has the dual functions of power quality control and regenerative braking energy recovery.In order to realize the coordinated control among the converters,a hierarchical control strategy composed of an energy management layer and a converter control layer is proposed.The converter control layer is em bedded in the energy management layer.In the energy management level,a state machine was introduced to switch the four operating modes of SCESS-RPC.In the converter control layer,Euler-Lagrange mathematical model of RPC was derived based on the study o f energy dissipation characteristics of RPC,and a nonlinear controller based on passi vity-based control(PBC)was designed.Based on the switching model of dc-dc converter,a linear quadratic regulator with integral action(LQRI)is studied.Finally,the complete implementation process of the hierarchical control strategy of SCESS-RPC(including the flow chart of the control algorithm,the reference power and the control block diagram of each controller)is given,and correctness of the proposed topology and hierarchical control strategy are verified by simulation and experiment.(5)Combined with the actual situation of a V /v traction substation,a unified power quality control system(UPQMS)engineering prototype composed of quadruple structured RPC and 3rd and 5th passive power filters was developed.The compensation scheme combining active device and passive device is adopted in this system,which has high cost-efficiency.Firstly,the basic structure and main transformer parameters of traction substati on are briefly introduced.Then,the topological structure,functional characteristics and parameter confi guration of UPQMS are described.The compensation principle and control strategy of UPQMS are analyzed in detail.Finally,combined with the field mea sured waveform and data,the power quality of traction substation before and after UPQMS compensation was quantitatively evaluated.The field operation results show that UPQMS can significantly improve the power quality of traction substation,so that its power quality assessment indicators can meet the national standard requirements.In addition,UPQMS can also effectively enhance the power supply voltage level of traction network,and improve the railway transport capacity and opera ting efficiency,which has excellent engineering promotion value.