Multilevel Inverter (MLI)-Based Stand-Alone Photovoltaic System: Modeling, Analysis, and Control

In this paper, a vector control scheme for a multilevel inverter (MLI)-based single-stage, three-phase, photovoltaic (PV) stand-alone system is analyzed. The power circuit employs a PV module-driven MLI, connected to the load/grid through a three-phase transformer having open winding on the MLI side. The control scheme is developed to supply real power even with the variable load and solar irradiance levels. The proposed control can ensure real power stable across the dc-link capacitors of the inverters, as well as satisfy the transient performance indexes of the PV stand-alone system. The dc-link voltage level of the MLI is well maintained throughout the operation to achieve desired power for delivery point by the designed scheme. The control scheme performance is established to be adequate in the simulation environment under different operating conditions. The robust stability, sensitivity, and good disturbance rejection analysis are conducted in this topology, and to evaluate the robustness of the controllers. Real-time results have been validated on a laboratory MLI PV-stand-alone system. Furthermore, the proposed topology results in high efficiency compared to the typical control schemes with the current total harmonic distortion within the limits. The theoretical claims are established with the real-time results successfully.