Stability Analysis Of Pv Grid-Connected Inverter Under Digital Control

In recent years,with the depletion of fossil energy resources and the proposal of the global energy Internet,the new energy represented by PV is attracting more and more attention from the human society.As an important interface to connect the new PV energy and the power grid,the grid-connected inverter is the most important part of the PV power station.And digital controller?DSP?has been widely used in engineering practice because of its powerful operation ability and anti-interference ability.Nevertheless,the zero-order-holder link and delay link are inherent in the digital control system,which makes PV grid-connected inverter easily being unstable.Based on this,the paper makes some research work on the stability analysis of PV grid-connected under digital control,and puts forward the stability criteria and related optimization design and compensation method of PV grid-connected inverter under digital control,which has some theoretical value and engineering significance.Aiming at sloving the problem of modeling of PV grid-connected inverter under digital control,the paper points out that the starred laplace transform has the same time-frequency characteristics with z transform.Based on this,the z domain model of the PV grid-connected inverter under digital control is derived without using the traditional transfer function approximation method.Aiming at sloving the problem of the stability analysis and parameters optimization design of PV grid-connected inverter under digital control,the mapping relation from s plane to z plane and the corresponding mapping formula are introduced.And take?/(3T_sa)as the boundary,the number of cross in-?-line is determined in different resonant angular frequency range baesd on the z-domain model.Then The number of open-loop unstable poles of the system is obtained by bilinear transformation.Combined with the Nyquist stability criterion under the view of Bode diagram,the stability criterion of PV inverter under digital control is obtained.And take critical resonant angular frequency?/(3T_sa)as the boundary,at the same time,combined with the increase or decrease of trigonometric function,the optimal design idea of PV grid-connected inverter is discussed in different resonant angular frequency range under the consideration of the changing of the grid impedance.Then through simulation and experiment,the correctness of the modeling of PV grid-connected inverter and the optimization design of related parameters under digital control is verified.Aiming at solving the problem of the unstable points,the idea of lagging compensation is put forward.And the typical lag link and notch filter lag link are analyzed,which leads to the conclusion that notch compensation has advantage in digital control.Meanwhile,the digital discretization method of notch filter is also studied.Then considering the change of the grid impedance,a specific design idea and step for lag compensation based on notch filter under digital control is put forward.The correctness of the design idea is verified by simulation and experiment.