Dead Time Harmonic Suppression Strategy Of Single Phase Grid Connected Converter

In today’s society,electric energy is the most important energy,all kinds of production and life are inseparable from it.However,due to the existence of some factors in the actual power system,they will introduce all kinds of harmonics after they are connected to the power grid,which will reduce the quality of the power grid current.Therefore,it is necessary to analyze the mechanism of these harmonics and find suitable methods to suppress them.In this thesis,the harmonic suppression strategy of single-phase grid connected converter is studied.In this thesis,firstly,the mathematical model of the single-phase grid-connected converter in the continuous domain and the discrete domain is established.Then,the mathematical expression of the output voltage of the converter is derived,and the generation mechanism of the output voltage harmonics is analyzed,and it is concluded that the harmonics introduced by the dead-time effect are the main reason.Next,two controllerbased harmonic suppression methods are studied: the harmonic compensation method based on resonance control and the harmonic compensation method based on repetitive control.In terms of resonance control,for the traditional resonance controller,the optimization method of phase compensation for the resonance controller is studied,and a method is proposed to maximize the distance from the Nyquist curve to the critical point(-1,j0).The parameter design method of the phase compensation angle and the design method of the resonant controller parameters are determined by the root locus method.In terms of repetitive control,by studying the system structure and performance,a new repetitive controller parameter design method is proposed.Compared with the traditional parameter design method,this method has higher system stability margin and faster error convergence.and the steady-state error is close to zero.Finally,it is verified by MATLAB simulation experiment and hardware-in-the-loop system.The experimental results show that the traditional resonant controller can only suppress the 7th harmonic at most,while the improved resonant controller can effectively suppress the 9th or more harmonics.And through experiments,it can be seen that,compared with the traditional repetitive controller,the improved repetitive controller can not only ensure the stability of the system,but also make the steady-state error close to zero,and the control speed is faster.