Research On Zeta Mode Multi-level AC/AC Direct Converter

Nowadays, it is rare in the world that the application of multi-level technique in ac/ac direct converter fields, so it is still in the period of science front researching. In this dissertation, Zeta mode multi-level ac/ac direct converter is investigated. Zeta mode three-level ac/ac direct converter is deeply investigated from aspects of topology, operation principle, control strategy, main steady operation characteristics, spectrum of voltage, stimulation verifier and optimization, prototype development and it's experiments. And a prototype of 500VA of Zeta mode three-level ac/ac direct converter is developed.Firstly, this dissertation presents technique of ac/ac converter, technique of multi-level and its application in the fields of ac/ac converter. Secondly, basing on the principle of three-level switch cell and the purpose of multi-level, two topologies of Zeta mode multi-level ac/ac direct converter are proposed, which are Zeta mode four-level and Zeta mode three-level. Compared with non-isolation and low or middle frequency isolation AC-DC-AC converter, it is single stage. And compared with Buck non-isolation AC/AC converter, it can realize buck and boost output voltage.In the main body of this dissertation, Zeta mode three-level ac/ac direct converter is deeply investigated. The non-complementary control strategy is proposed to it. Compared with complementary control strategy, it makes the converter more reliable. It can protect the converter from operating in the state of that no operation modes works at the switching time of operation modes. It also makes sure that more operation modes can't work at the same time. The dissertation also presents the main steady characteristics, the ripple of current through inductor and voltage across capacitor. Comparison of the voltage spectrums between Zeta mode three-level, Buck and Cuk two-level ac/ac direct converter verifies that three-level can get a better spectrum, so it can reduce the bulk of the filter and improve the quality of output voltage. The stimulation verifies the theory analysis and optimizes the parameters of the prototype. The experiment results of the prototype are given in cases of three kinds of loads.Finally, a conclusion of the dissertation is made, and further research to the application of multi-level in the fields of ac/ac direct converter is prospected.