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A common practice in the analysis of voltage source inverters is the assumption of a voltage-type input source even in the case of renewable energy sources (RES). When a converter is supplied by an RES, such as a photovoltaic (PV) generator, the dc-link voltage is usually controlled by the inverter to extract maximum power from the source. This study presents an improved dynamic model of grid-connected three-phase renewable-energy-related inverter. For the proposed model to correspond to reality, the true nature of the input source has to be taken into account: an input-voltage-controlled converter has to be analysed so that it is supplied by a current source. Since all real sources are non-ideal, an explicit method to include the source effect on the inverter dynamics is presented, which has not been previously published in the literature. This study shows that the dynamics of the converter change completely when the operating point of a PV generator shifts from the constant current to the constant voltage region. This study shows also that assuming a voltage-type input source for a PV inverter leads to a model that cannot predict the existence of higher-order dynamics and a right-half plane zero in the control-to-output transfer function.
Date of Publication: November 2012