Modeling and performance analysis of multilevel inverter for single-phase grid connected photovoltaic modules

Power electronic converters always have been circuits of difficult modeling because differential equations that describe them have discontinuities. Although this situation has been improved since the appearance of the bond graph approach, able to jointly describe both continuous and discrete behaviors exhibited by some physical systems, nowadays it is possible to obtain very precise models which help us in the study and design of such circuits. This work gives an overview on single-phase grid converter based on seven level diode clamped multilevel inverter for photovoltaic system with maximum power tracking. In the first part, we develop a bond graph model of the inverter. A bond graph MPPT strategy is developed, the performance of the algorithm is studied. Then, we present the bond graph model of solar cell. Thus, we study a cascade constituted by tow photovoltaic cell panels - five-level NPC VSI - permanent magnet synchronous machine (PMSM) fed by photovoltaic PV energy systems at different illuminations. At the full solar intensity, the maximum power point of current/voltage I/V characteristic of the PV modules is designed to be at the rated conditions of the machines. The steady-state output characteristics, the torque-speed characteristics, of the three DC motors with the two inputs are presented and compared.