| With the continuous development of China’s railway industry,traditional diesel locomotives have been gradually eliminated,and electric locomotives with the characteristics of energy saving,environmental protection and high efficiency occupy a dominant position in China’s railway transportation.Because there are many nonlinear components in the converter circuit in the locomotive,and there are various complex working conditions in the operation of the electric locomotive,which will cause more harmonics in the operation of the locomotive,endanger the power system and produce unnecessary losses,so we must pay special attention to harmonic control.In order to establish the mathematical model of the main circuit of the locomotive,this paper first needs to study the main circuit of the locomotive,but because the electric locomotive has complex working conditions in the running process,it is necessary to consider the running status of the locomotive under actual conditions.To solve the current taken by locomotive,the iterative method can be used to calculate it first,and then the mathematical expression can be finally solved by FFT,and the magnitude of harmonic current in the main circuit of locomotive under different working conditions and the influence of harmonic current on power factor can be analyzed.Then,the control characteristics of SS4 electric locomotive are introduced in detail,and its main components are described.The simulation model is built by MATLAB/Simulink,and the changes of current and voltage waveforms and harmonic content are analyzed from the simulation results when the locomotive runs under traction conditions.Secondly,the function of four-quadrant rectifier in traction drive system of HXD3 electric locomotive is analyzed,and the rectifier circuit of the original SS4 electric locomotive is optimized and designed by using its characteristics.The working principle of fourquadrant rectifier is expounded in detail,and its harmonics are analyzed This paper introduces the application of unipolar and bipolar PWM modulation methods in singlephase voltage source four-quadrant rectifier.The control strategy of four-quadrant rectifier is analyzed.Aiming at the problems of traditional SS4 electric locomotive in operation,a new main circuit is designed by using four quadrant rectifier,and the working principle of the circuit under different working conditions is analyzed.This paper introduces IGBT in detail,including its structure and working principle,and verifies the correctness of the model by selecting the appropriate type of IGBT and its drive and modeling its simulation.Based on the transient direct current control strategy,the simulation model of single-phase four-quadrant rectifier is established by MATLAB/Simulink using the IGBT and its driving model Finally,the Boost boost circuit is designed and the corresponding simulation model is established.Finally,the hardware and software of the system are designed,the required STM32 chip model is determined,and the peripheral circuits such as voltage detection circuit and IGBT buffer circuit are designed.The duty ratio of PWM wave is controlled by STM32 timer,and the output PWM waveform is used to realize the rectification and inversion process.Establish corresponding system experiments to verify the correctness of the design.With the IGBT model,drive model and Boost circuit model established in chapter 4,the optimized simulation model of SS4 electric locomotive main circuit is established through MATLAB/Simulink simulation platform.The voltage,current waveform,harmonic spectrum and power factor curve of transformer secondary side are analyzed according to different operating conditions of the locomotive.The correctness and feasibility of the main circuit design are verified by observing the simulation results. |
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