Seven-level grid-connected packed U-cells inverter using photovoltaic generators system

In this article, one of the most recent multilevel converter topologies named packed U-cells is developed for three-phase grid-connected inverter mode using photovoltaic input voltage sources. This topology makes a very important research subject in what concerns the adaptation of multilevel inverters with photovoltaic systems. According to the literature, it is well applicable with the string type and suitable for high-voltage applications because the number of switches is less than conventional topology and maximum blocking voltage is U-dc and 2U(dc); however, it is not applicable for multistring type and unsuitable for the central type because it is based on isolated DC source. The packed U-cells topology is highly optimized from the point of view of the number of passive and active components. The output voltages of our converter are composed by seven levels obtained by the auxiliary buses voltages regulation. In order to obtain the DC input voltages of 120 V for the inverter, photovoltaic generators are connected to a boost converters. The maximum power point tracking method based on the Perturb and Observe was used to improve and optimize the performance of the photovoltaic system control in the simulation part. The grid-connected PUC7 inverter operates with a unit power factor and injects active power into the grid. The control is configured to make the current waveform in phase with the AC voltage waveform. Reference angle variations have been made to operate with different power factors to test the performance of the applied control and the influence of these variations on the auxiliary buses voltages regulation. The simulations were done under Matlab/Simulink platform and have been experimentally verified using dSpace 1104 controller board and three-phase packed U-cells inverter composed by nine half-bridge insulated-gate bipolar transistor modules.