Numerical modeling and research on nonlinear dynamic behaviors of two-stage photovoltaic grid-connected inverter

In this paper, the piecewise smooth state equation of a two-stage photovoltaic grid-connected (TPG) inverter is established and studied; based on the solution to the piecewise smooth state equation of the TPG inverter, effects of the photovoltaic array voltage on nonlinear dynamical behaviors of the TPG inverter are analyzed by using bifurcation diagram, folded diagram, 3D phase diagram, and Poincaré section. Then the nonlinear dynamical behaviors of TPG inverter are compared with the conventional one. And a strategy of expanding the input voltage range for the TPG inverter is explored. Finally, the nonlinear dynamical behaviors in it caused by the variation of main circuit parameters: such as the output inductance and capacitance of the front-stage, as well as those of the second-stage, are discussed through slow-scale bifurcation diagrams. Studies have found that it is effective to expand the input voltage range of the TPG inverter by segment control of the photovoltaic array voltage, and the chaotic phenomena in the TPG inverter can be avoided by increasing the parameter values of inertial devices such as output inductance and capacitance in the front-stage appropriately, but the values of output inductance and capacitance in the second-stage should be away from the multiple noncontiguous region, since it can cause chaotic behavior. The above work may have important guiding significance and application for improving the stability and efficiency of two-stage photovoltaic grid-connected inverter based photovoltaic power generation system.