Research On The Technology Of Negative Sequence Compensation And Utilization Of Regenerative Braking Energy For High-Speed Railway

As the main artery of the national economy,electrified railway,especially high-speed electrified railway has an important role in the national economic and social development.Although the power electronics technology promotes the rapid development of high-speed rail technology,the non-linearity of power electronic equipment and the power supply mode of electric locomotive have caused more and more serious problems in power grid and traction power supply system such as negative sequence and regenerative braking energy impact,which has been paid more and more attention by academia and industry.Railway Power Conditioner(RPC)can achieve system balanced and restrain impact by dynamically adjusting active and reactive power,which is a revolutionary advancement in the field of power quality management of traction power supply system.However,the traditional RPC technology is not mature to solve these problems.In this paper,the mechanism of high speed railway negative sequence compensation and regenerative braking energy feedback are studied in detail.The main contents are as follows:(1)Firstly,the power quality control technology and its application in traction power supply system are discussed.Then,the power quality characteristics of traction power supply system are analyzed and compared in detail,and the status of RPC technology is summarized and its development trend is pointed out.Finally,this paper expounds the significance of the subject.(2)A DC voltage compound control strategy is proposed to solve the problems of low response speed and large overshoot of the DC side voltage of RPC.The PI parameters are dynamically adjusted by establishing the relationship between the DC voltage error and the PI parameter.The response speed of the system is improved and the overshoot is reduced.The accuracy of the method is verified by experiments.Considering the effect of the voltage distortion of the power supply arm on the compensation current of RPC,an AC current compound control strategy is proposed.The dynamic performance of the system can be effectively improved by adding the feed-forward link on the basis of QPR control.Compared with QPR control strategy,the compound control strategy reduces the effect of the voltage distortion of the power supply arm while ensuring a good negative sequence control effect.(3)Considering the capacity design problem of HPQCS,the HPQCS asymmetric compensation principle is discussed by analyzing the topological structure of HPQCS,and the HPQCS asymmetric compensation capacity calculation formula is deduced,and the symmetrical compensation capacity and non-Symmetrical compensation capacity were compared and analyzed.In order to reduce the running current and loss of the system and improve the long-term running ability of HPQCS,the principle of negative sequence optimization compensation is studied,and the difference between full compensation and negative sequence optimization compensation is analyzed.In order to calculate the compensation current in real time under different load conditions,the relationship between the voltage imbalance and the compensation current is studied.The method of calculating the optimization compensation of the negative sequence is deduced,and the calculation method of an on-line real-time compensation current for different load conditions is proposed.The effectiveness and feasibility of HPQCS negative sequence optimization compensation are verified by numerical examples and simulation experiments(4)Considering the problem that regenerative braking energy utilization of electric locomotives is very low and the difference between the peak power and the valley power of traction transformers is very large,a novel SC-PQCS,which is composed of RPC and super capacitor(SC)energy storage devices,is proposed in this paper.The SC-PQCS topologies and bi-directional DC-DC converters are analyzed,and the main parameters of the system are designed.The slow charging-up power setting value and peak power setting value are added,three new working modes are analyzed and the equivalent circuits of SC-PQCS and RPC are constructed.The regenerative braking energy utilization rate of two compensation systems are compared and analyzed.The simulation results show that the system can not only solve the negative sequence problem of high-speed rail power supply system,but also can greatly enhance the regenerative braking energy utilization rate of electric locomotives.The system utilizes the valley electric energy to cut off the peak electric energy,which improves the utilization rate of the transformer effectively,the proposed system has good theoretical research value and engineering application prospect.In this paper,lOkVA experimental prototype is developed.The main circuit diagram,main controller,driving circuit,connection reactance and DC capacitance of the prototype are designed,and the parameter calculation method is given.The experimental results show that the main performance of the experimental prototype has achieved the expected design goal.The proposed mechanism of negative sequence compensation of high speed rail and the regenerative braking energy enrich and improve the high-speed rail power quality management theory and technology system,which provide reference value for other similar systems.