Design and control of a grid-tied three-phase three-level diode clamped single-stage photovoltaic converter

This paper introduces a single-stage grid-connected photovoltaic power conversion system based on a three-phase three-level Neutral Point Clamped (NPC) converter. The main benefits of the proposed structure are the elimination of the intermediate DC/DC power conversion stage that is usually used to boost the dc-voltage and ensure MPPT operation. Therefore, two control schemes based on a current controller and an MPPT algorithm are handled in only one processing stage. The MPPT algorithm computes in real-time the dc voltage that should be applied across the PV generator so as to extract the maximum power. The output of the MPPT algorithm is thereafter considered as a reference of a current controller that should perform a perfect tracking of the dc-voltage reference and also near unity input power factor operation. The proposed photovoltaic power conversion topology and control method are tested by numerical simulations. The obtained results demonstrate that the designed PV conversion system provides effective response in steady state, fast and perfect tracking of the maximum power point, and robust in case of a partial shading.