Simple VSI-based single-phase inverter: Dynamical effect of photovoltaic generator and multiplier-based grid synchronization

Photovoltaic generator is internally a current source with nonlinear characteristics resembling both current and voltage source depending on the operating point in respect to the maximum power point. In order to transfer maximum power, input voltage of the inverter has to be controlled in addition to grid current control, resulting in cascaded input-output-control scheme. For proper modelling, the input-source characteristics and the input voltage control cannot be omitted. It is observed that the cascaded-control scheme produces negative-resistor-like behaviour at the inverter output, which is amplified by the multiplier-based grid synchronization. The negative impedance makes the inverter prone to instability and the utility grid for harmonic resonances.