Optimal Control Of Single-phase Three-level Rectifier In Traction Locomotive

In order to meet the needs of economic development in the new era of our country,the electrified railway business has developed rapidly.At present,the traction drive system of electric locomotives has been upgraded from DC drive to AC drive.As an important part of the AC drive system,the grid-side pulse rectifier is responsible for grid-side power factor correction,reducing pollution to the grid and stabilizing the intermediate DC voltage,etc.It is an important task,and it is of great practical significance to carry out in-depth research on it.This paper takes the single-phase pulse rectifier with NPC three-level structure as the research object,analyzes its topological structure and working principle,and establishes the mathematical model of the rectifier in the conventional coordinate system,which provides a theoretical basis for the design of the control algorithm.According to the mathematical model,a double closed-loop control system is built,and the parameter models of the inner and outer loop controllers are deduced.Considering that the pulse rectifier undertakes the task of reducing harmonic pollution,the causes of low and high harmonics in the grid-side current are deeply analyzed,and the direction for the design of the control algorithm is set.Aiming at the harmonic pollution of grid-side current,two conventional control strategies are studied: current decoupling control based on dq coordinate system and transient current control.Based on transient current control,a cascaded QPR controller is designed.This method can realize non-steady-state error control of AC quantity,and can effectively suppress loworder harmonics in grid-side current.Also based on transient current control,a repetitive controller with a special structure is designed.This method enables the system to track the periodic given signal without static error,and realizes the effective suppression of low and high harmonics by amplifying the repetitive components in the error signal.The control algorithm is simulated based on MATLAB/Simulink simulation platform,and the results show that both control algorithms have good harmonic suppression ability.Two modulation algorithms of single-phase three-level NPC PWM rectifier are studied:CBPWM and SVPWM.The working principle of the SVPWM algorithm is analyzed emphatically,the influence of various vectors on the midpoint potential is discussed,the synthesis method of the vector and the calculation method of the vector action time are studied.According to the different vector action sequences,SVPWM is divided into Five-part and Three-part.The reasons for the offset of the midpoint potential on the DC side are discussed,and two midpoint potential control algorithms are studied for the Five-part and Three-part,respectively.In order to reduce the average switching frequency and the switching loss of the rectifier,a compound modulation algorithm with hysteresis is proposed.Based on the MATLAB/Simulink simulation platform,the simulation experiment of the mid-point potential control algorithm is carried out.The results show that the three algorithms can effectively control the mid-point potential,and the compound modulation algorithm with hysteresis can effectively reduce the average switching frequency of the rectifier.The hardware experimental platform of single-phase three-level NPC PWM rectifier is built,and the control algorithm and modulation algorithm are experimentally verified based on d SPACE.The experimental results prove the correctness and feasibility of the algorithm.