Controlling a Grid-Connected T-type Three Level Inverter System Using a Sliding Mode Approach

In this work a multilevel inverter based grid connected photovoltaic system is presented. It is used a T-type multilevel inverter. This inverter is based on a classic three-phase voltage source inverter. However, in order to increase the number of voltage levels, three extra bi-directional switches are used. These switches are connected between the three-phase terminals of the inverter and a common point of the two DC-capacitors. The inverter is connected to the photovoltaic panel through a DC/DC converter and to a three-phase transformer. The DC/DC converter and the multilevel inverter are controlled using a sliding mode controller. At the output of the controller associated to the multilevel inverter is used a vectorial modulator. This modulator will also be used to ensure the DC voltage balancing of the capacitors connected to the inverter. A maximum power point tracking algorithm associated to the photovoltaic generator is also presented. Several results are presented in order to confirm the characteristics of the proposed system.