Research On The Harmonic Stability Of Photovoltaic Grid-connected Inverter System

Twice times industrial revolution progress was associated with the energy consumption exponentially increasing, lack of fossil energy such that more and more people pay attention to new energy technology. With the scale of PV power generation expanding, photovoltaic power generation requirements have become more and more demanding. In the case of weak grid, grid impedance has been impact on the PV grid system, which can lead to a serious deterioration in the overall system. In this paper, we take the photovoltaic grid inverters as the target,and analyze the harmonic stability of PV grid system.Firstly, this paper derive PV grid-connected inverter output impedance model under the ideal inverter, and then analyze the impact of some nonlinear factors in non-ideal inverters. It provides theoretical support for subsequent analysis. Secondly, this paper study the mechanism of the system harmonic resonance problems. For the system instability problems caused by grid impedance overload, we can take Nyquist stability criterion method to determine the stability of system. Modal analysis method can be used for further analysis of PV grid system harmonic resonance problems, and according to its sensitivity theory, this paper can determine which grid element has a greater impact on harmonic resonance. Thirdly, phase-locked loop based on double second order generalized integrator (DSOGI-PLL) under harmonic is vulnerable to dc-component, so this paper gives an improved method of dc-component elimination on DSOGI-PLL. Finally, we build the simulation model by the matlab/simulink. The simulation results show the effectiveness and feasibility of above theory and experiment proves the feasibility of analysis for the system instability.