| Three-phase PWM rectifier has been widely used because of it's strong controllability,great sinusoidal performance,high power factor and high power utilization.To focus on the problems of stability and safety of three-phase PWM rectifier reliable operation.The thesis has done the related research to improve adaptability against grid voltage fluctuation and capability of outputting higher power safely.Firstly,three-phase rectifier's control effect is dependent on some factors include the quality of grid-voltage.The operation effect of PWM rectifier is affected by grid voltage,DC link voltage would increase even out of control as high positive fluctuation occurred.In this thesis,the DC link voltage control characteristics was analyzed in detail.Based on a method to control rectifier's power factor through injection reactive power,three types of grid-voltage adaptive control strategies were designed by injecting reactive current.One of the easily realized method was choosen by analysis and simulation,controller paraments tuning method was designed also.Simulation and experiment results verify the proposed control strategy valid and can be applied to practice.Secondly,in order to adapt higher power output level applications,rectifier parallel structure was widely consided to use.Parallel three-phase PWM rectifiers system would produce circulating current and affect the reliable operation.In this paper,the principle and categories of circulating current were analyzed in detail.The control strategy of circulating current rejection was designed which adjusted the allocation of zero vectors' duty ratio in SVPWM based on PI controller.The useful effect to circulating current rejection of this method was verified by simulation. |
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