Abstract
For sustainable development, promotion of installing renewable energy systems has become one of the most popular issues recently. For handling larger power, a three-phase inverter is chosen for connecting to a medium/high voltage grid system. However, due to the limited voltage rating of power devices, a multilevel converter is usually adopted. Moreover, to increase the efficiency, a single-stage converter configuration is preferred than a two-stage converter. Therefore, the objective of this thesis is mainly focused on developing a novel single-stage single-phase multilevel inverter for renewable energy systems. Naturally, a three-phase system can be synthesized easily with three single-phase modules.Basically, the contributions of this thesis can be summarized as follows. First, a novel single-phase single-stage five-level inverter topology with electrical isolation is proposed. Based on the generalized zero vector (GZV), it is seen that the conventional two-stage inverter can be integrated into a single-stage one to simplify the configuration and enhance the efficiency. Compared with the conventional inverter, only six active switches instead of eight switches are required. The proposed inverter can still keep the advantages of a conventional multilevel inverter. In addition, among them, two active switches are operated under very low switching frequency. Next, the corresponding mathematical model of the proposed converter is derived for convenient controller design of the converter. Finally, a 200W, 20V DC input and 110Vrms AC output prototype is constructed for verifying the effectiveness of the proposed five-level inverter. The maximum efficiency can be maintained to about 90.9% approximately with a rather flat profile form full load up to 20W.