The Research On Suppressing Influences Of Rippled DC Voltage In Traction Converter

In electric traction drive system,there is ripple voltage on DC side,due to single-phase power supply on grid side and topology of single-phase PWM rectifier.In order to reduce the weight of high-speed EMUs,the LC resonant filter in the traction converter is removed,resulting in that the ripple voltage could not be effectively absorbed,which will affect the stable operation of the traction converter.So this thesis focuses on the strategy of suppression ripple voltage’s effect in traction converters without LC resonant filter.Firstly,the cause of ripple voltage is studied.The effect of ripple voltage on grid current and traction motor is analyzed quantitatively.Secondly,in order to suppress low harmonic current on grid-side,The voltage dynamic compensation and the post-positional digital filter are proposed in the external voltage loop adopts,and studies the parameter and discrete method of the low-pass filter,trap and filter combination,then ripple component in the given current is filtered.In the current inner loop,the odd-harmonic repetitive controller is redesigned,and the parameters are optimized.meanwhile,the method of designing quasi-proportional resonant controller with phase compensation and its parameter design are discussed.The odd-harmonic repetitive controller and the proportional resonance controller based on internal model principle have improved the ability of the single-phase PWM rectifier to track the AC signal.Then,in multi-mode PWM strategy,the SHEPWM was used online fitting instead of off-line optimization.Based on the principle of volt-second balance,beat-less control ctrategy in the full-speed range of motor is studied.When the carrier ratio is big,the traction inverter adopts feedforward compensation to correct the trigger pulse width in real time.At low carrier ratios,the traction inverter uses frequency compensation to dynamically modify the frequency of output voltage.To better suppress the beat of motor,periodic prediction is used to compensate for the delay error caused by the PWM update.Segmented use of the two compensation algorithms suppresses beat current and torque ripple.Finally,simulation model of traction converter is builted in Matlab/Simulink.The algorithm for suppressing the low-harmonics gird current and different beat-less control algorithms are simulated Through the study the data of simulation,the correctness and effectiveness of the proposed method are verified.