Nonlinear Behavior And Control Of Single-Phase Photovoltaic Grid-Connected Inverter

Power electronic system is composed of many switching devices.During operation,there will be nonlinear phenomena such as oscillation,bifurcation and chaos,which will threaten the stability of the system,make the system performance fail to achieve the expected effect,and in serious cases,it will lead to system collapse.As a typical power electronic system,grid connected inverter is widely used in photovoltaic power generation system,which has rich nonlinear dynamic behavior.Based on the bifurcation and chaos theory,this paper studies the nonlinear behavior and control of single-phase photovoltaic grid-connected inverter.The main research contents of this paper are divided into the following aspects:(1)Taking the single-phase photovoltaic grid-connected inverter under proportional control and proportional integral control as the research object,the discrete iterative model of the system is established based on the stroboscopic mapping theory;The evolution process of the system from bifurcation to stability in time domain is described by the Fourier diagram and the numerical analysis of the bifurcation parameters in time domain;The stability of the system is analyzed theoretically according to the eigenvalues of Jacobian matrix,and the stable working region of the system under multi bifurcation parameters is obtained.(2)Quasi proportional resonance regulator can make up for the defects of traditional control strategy and reduce the interference of grid side voltage to photovoltaic grid-connected power generation system.This paper studies the nonlinear characteristics of single-phase photovoltaic grid-connected inverter under quasi PR regulation.Firstly,the discrete iterative model of the first-order single-phase photovoltaic grid-connected inverter with quasi proportional resonance regulation is established.The evolution process of the system from stability to period doubling bifurcation and gradually entering chaos with the change of parameters K_P and L are described by numerical simulation method;The stability of the system is analyzed by Jacobian matrix method,and the stability region of the system under K_P-L double bifurcation parameters is obtained.Then,the discrete iterative model of the third-order single-phase photovoltaic grid-connected inverter under quasi PR regulation is established,and the stable working range of the main circuit parameters and control coefficients of the system is determined through the bifurcation diagram;According to the characteristic value of Jacobian matrix,the stable working region of the system under double bifurcation parameters and three bifurcation parameters is obtained,and the calculation method of determining the oscillation frequency when the system oscillates is given;Finally,the correctness of the theoretical analysis is verified by physical experiments.It is found that the essence of low-frequency oscillation after system instability is Hopf bifurcation;Compared with the first-order single-phase photovoltaic grid-connected inverter under quasi PR regulation,the total harmonic distortion of the grid connected current of the third-order single-phase photovoltaic grid-connected inverter under quasi PR regulation is smaller,and the stable working range of the control coefficient K_p is larger.(3)The time-delay feedback method,extended time-delay feedback method and second-order band stop filter method are applied to the chaos control of the first-order single-phase photovoltaic grid-connected inverter under quasi PR regulation,the corresponding discrete iterative model is established,and the bifurcation diagrams of the system under different control parameters are obtained;The effectiveness of the three chaos control methods is verified by Matlab/Simulink simulation.The results show that the three chaos control methods can effectively control the nonlinear phenomenon of the system,and can expand the stable working range of the proportional coefficient K_p of the quasi PR controller.When the second-order band stop filter is used to control the nonlinear behavior,the stable working range of the control parameters is much larger than that of the delay feedback method and the extended delay feedback method.From the perspective of nonlinear dynamics,this paper deeply studies the nonlinear behavior of single-phase photovoltaic grid-connected inverter with different control strategies,which can provide theoretical guidance for practical engineering design and parameter debugging.The chaos control method can well suppress the nonlinear phenomenon of single-phase grid-connected inverter,so as to expand the stable working range of the system,which has certain engineering significance.