Modeling, analysis, and implementation of a photovoltaic grid-tie inverter system

Modeling of a complete photovoltaic (PV) inverter system poses a significant challenge because it involves different time-scaled dynamics including filter elements, fast current loop, voltage loop, maximum power point tracking (MPPT) loop, and response of the energy source. This paper intends to utilize the state-space modeling approach for stability analysis for a grid-tie PV inverter system by eigenvalue evaluation with different irradiation levels, PV output voltages, voltage-loop gains and current-loop gains. The stability analysis can not only show more insight of the two-loop interaction with current-loop gain variation, but also show the stability trend due to the change of both the source voltage and the source impedance with the input PV voltage change, which are quite difficult to detect with conventional single-variable transfer function analysis. The controller based on state-space modeling and analysis has been designed and implemented. Experimental results are used to verify the stability trend predicted in the model.