부산대학교 도서관

In this article, a multilevel single-phase converter is proposed and investigated. Its structure is based on cascaded-transformer systems, which are very interesting in applications in which a single dc source is available. The features of well-known multilevel cascaded H-bridge and transformer-based solutions are integrated into the proposed converter. As a result, the number of synthesized voltage levels can be optimized without excessively increasing the number of transformers. The basic configuration has six two-level insulated-gate bipolar transistor legs, two injection transformers, and two dc links (the lowest voltage dc link may be a floating capacitor or be connected to a small dc power source). The configuration is generalized and the calculation of the transformer's turns ratios as well as the dc-link voltages to maximize the number of voltage levels is provided. The proposed configuration is compared with cascaded H-bridge and a single-phase shared leg converter, which are also cascaded by means of transformers. Compared with the conventional converters, the proposed one has lower switching losses and higher conduction losses. Thus, the proposed configuration is more interesting in terms of semiconductor losses for high-voltage and low-current applications. Experimental and simulation results are shown to demonstrate the feasibility of the system.