| The rapid development of electrified railway in our country brings many power quality problems such as harmonic,reactive power and negative order current to the railway traction power supply system.They not only affect the stable operation of the railway system,but also bring a huge negative impact to the upstream public power grid.In order to better control the power quality problems in the traction power supply system mentioned above,experts and scholars use modular multilevel converters in traditional railway power regulators(RPCs).MMC)technology constitutes a new type of railway power regulator(MMC-RPC),Due to its high pressure resistance,large compensation capacity,good dynamic and static performance,and the advantages of being directly connected to the traction network without the need for Buck Transformers,it stands out in many electric power compensation devices.In this paper,the following work and research are done for the traction power supply system connected with MMC-RPC using V/v Transformer:In this paper,the power quality problems in traction power supply system are analyzed in detail,and the negative order,harmonic and reactive power problems in traction power supply system are analyzed.A brief introduction of various management schemes used by many scholars in the past has been made,and it has been found that none of them can effectively control the power quality problems in the traction network.Through the study,it was found that the use of modular multilevel converters(MMC)in the traction network of the Railway Power Regulator(RPC)can effectively solve the power quality problem in the traction power supply system during steady state.However,the operating conditions of electric locomotives are generally more complex,and the system is often in an unstable state where the load and system frequency fluctuate.Under such complex conditions,the governance effect of MMC-RPC will be affected.In order to improve the ability of MMC-RPC to adapt to various working conditions and its governance effect,this paper uses MMC-RPC modeling to understand the MMC-RPC working principle.This paper analyzes the transformation of mathematical models in the normal time domain ? ?? coordinates ? dq rotation coordinates,and constructs the orthogonal virtual component ? axis of the output signal by means of second-order generalized integrals to complete the conversion process.Secondly,through the extraction and analysis of the current and power compensation instructions in the traction power supply system,it is found that MMC-RPC can not only effectively control the power quality problem in the traction power supply system on the basis of the traditional second-order generalized integrator combined with the locking frequency ring.It also improves the adaptability of MMC-RPC to frequency changes in traction power supply systems and enhances the reliability and feasibility of MMC-RPC in traction power supply systems.Finally,SOGI-FLL is used in double closed-loop control and proportional integral resonance controller.Through Matlab / Sumilink simulation,it is verified that SOGI-FLL is used to replace the second-order generalized integrator and phase lock ring in MMC-RPC.When the operating conditions of the system change,it has a good ability to adapt to the frequency and has a good effect on the power quality of the traction power supply system. |
PDF Full Text Request