| China has developed a series of electric locomotives with independent intellectual property rights since 1956.The efficiency of railway transportation in China has been greatly improved.However,with the progress of science and technology,the traditional phase-controlled rectifier and two-level PWM rectifier can not meet the needs of some high-voltage and high-power electric locomotives.Three-level PWM rectifier has been gradually applied to some high-voltage and high-power converter systems of electric locomotives due to its high voltage withstanding capacity and good harmonic characteristics.In this paper,the diode-clamped single-phase three-level PWM rectifier used in the CRH2 EMU is taken as the research object,and the research on the SVPWM modulation technology of the rectifier is carried out based on the transient current control strategy by referring to the research of domestic and foreign experts and scholars on three-level PWM rectifier.In order to inherit the advantages of SVPWM modulation,such as high voltage utilization,low harmonic content,easy neutral-point voltage balance and convenient digital control,the SVPWM modulation technology commonly used in three-phase system is used instead of SPWM modulation technology in single-phase three-level PWM rectifier.Firstly,this paper studies the four-quadrant working principle of PWM rectifier,analyzes the nine switching states and corresponding switching functions of single-phase three-level PWM rectifier in detail,and establishes a unified mathematical model.Several control strategies of rectifier,SPWM and SVPWM modulation technology are deeply analyzed.This paper analyzes the causes of neutral-point voltage offset in rectifier from two perspectives of equivalent circuit model and mathematical model,and puts forward specific solutions combining with SVPWM modulation technology,and deduces specific modulation sequence.Then the simulation model of rectifier is built based on MATLAB/Simulink.The performance of SPWM modulation technology and SVPWM modulation technology in different working conditions is analyzed by this model.The feasibility of the neutral-point voltage balance control strategy based on SVPWM modulation technology is verified by this model.Finally,a low-power experimental platform is built based on TMS320F28335.The hardware circuit composition,device selection and DSP program design of the experimental platform are introduced in detail.The feasibility and practicability of the proposed SVPWM modulation strategy based on transient current control are verified by the experimental platform. |
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