Research On Control Of PWM Rectifier Under Non-ideal Grid

As an essential power electronic converter,PWM(Pulse Width Modulation,PWM)rectifier has some considerable merit which includes energy bidirectional flow,unity power factor,slighter fluctuation of DC-bus voltage and so on.This paper researched on the different control strategy of PWM rectifier for different application scenarios under non-ideal grid.Firstly,the three-phase PWM rectifier is the first research object in this paper.In the application of wind power generation,the grid cannot be guaranteed to work ideally all the time.It provides higher control requirements for three-phase PWM rectifier as the wind power grid side converter.This paper briefly reviews generation principle and influence factors of the current harmonics.In order to realize the goal of grid-side current harmonic reduction,this paper studied the traditional control strategy,resonance control strategy and repetitive control strategy respectively under unbalanced grid voltage.In the end,the above results are verified by MATLAB simulations and experiments.Secondly,for high power rectifiers,due to the limit restriction of the switching loss,operating at low switching frequency is indispensable,which brings about a heavy cross-coupling between the current components.In this paper,an effective approach is proposed to realize decoupling.A complex vector current regulator at low switching frequency are employed in this approach which is based on discrete-time domain to achieve dynamic property and the stable state performance.In addition,the parameter design method of LCL filter is introduced.And this paper also researches the dynamic process at the voltage drop time.Besides,railway traction single-phase PWM rectifier is the other research object in this paper.The control characteristic of single-phase PWM rectifier is studied,under the non-ideal grid.First,this paper analyzes the reason why the current harmonics generated.In order to realize the goal of grid-side current harmonic reduction,this paper applied the resonance control strategy combined with trap filter to achieve grid-side current harmonic reduction.In the end,the above results are verified by MATLAB simulations and experiments under distorted grid.