Research On Control Strategys Of A High Power IGCT-based Three-level PWM Rectifer

This paper focused its researches on high power IGCT-based three-level PWM rectifiers. Theory analysis, software simulation, prototype experimentation and other methods were made to investigate the problems of the three-level IGCT PWM rectifiers including its mathematical model, control strategy and modulation. Harmonic analysis of the rectifiers was made in this paper. Solutions to the problems of the high power IGCT PWM rectifiers in engineering application were also discussed.The mathematical model of PWM rectifier was derived in this paper. The VOC control method was designed with foundation of its mathematical model. The AC-side dq frame model of a PWM rectifier was derived along with its instantaneous power balance model. The double closed-loop VOC control system with load feed forward was built according to the below models.The space vector modulation technique of the three-level PWM rectifier was introduced. The simplified algorithms of the three-level space vector modulation were derived. The advantages of the PWM rectifiers using space vector modulation were discussed. The harmonic analysis of the AC-side output phase-voltage of the three-level PWM rectifier with IGCTs was made later. The foundation of harmonic analysis of the AC-side output current was laid.The relationship between the short-circuit impedance in AC-side transformer and PWM rectifier was discussed in this paper. The modulation indexes of PWM rectifier working in different conditions with different short-circuit impedance in AC-side transformer were computed. The harmonic of AC-side output voltage can be computed with the different modulation indexes of the rectifier working in different conditions. And the harmonic of AC-side output current can be computed by the harmonic of the output voltage and the short-circuit impedance in the incoming line transformer. Then the design of the incoming line voltage with optimal harmonic was given.Research was made to solve the problems of the IGCT three-level PWM rectifier in engineering application, including the compensation of the space vector modulation in PWM rectifier and the starting strategy of the rectifier. The dynamic compensation strategy was give by analysis the cause of it in the practical discrete control system. And the dynamic compensation strategy was proved by PSIM simulation and prototype experiment.