Development of energy efficient photovoltaic microinverter

Edvardas Bielskis

Doctoral dissertation

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The aim of the performed research is to improve the efficiency of the photovoltaic grid tied microinverter and reduce the nonlinear distortions of the microinverter current supplied to the electricity network. An energy-efficient single-stage photovoltaic microinverter has been developed and investigated. The control algorithm and the controller has been developed for the tracking of sinus shape of the microinverter output current. The investigation was performed using simulation and experimentally.

The dissertation consists of an introduction, three chapters, general conclusions, references and the list of author's publications on the topic of the dissertation.

 The research problem, the relevance of the work, the object of research are presented in the introductory chapter. The aim and objectives of the work, the research methodology, scientific novelty of the work, the practical significance of the work results, defended statements are presented as well. At the end of the introduction, the author's publications and conference papers on the topic of the dissertation and the structure of the dissertation are given.

In the first chapter, the research analysis of the properties of photovoltaic inverters is performed. The principles of operation of photovoltaic microinverters are analyzed, their advantages and disadvantages are discussed, microinverter output current control systems are analyzed. DC-DC (DC – direct current) voltage converters used in microinverters are reviewed. The tasks of the dissertation are formulated.

The experimental investigation results of efficiency of a developed DC-DC voltage flyback converter with an alternative active surge suppression circuit and a two-switch DC-DC flyback converter are presented in the second chapter. A new single stage grid tied photovoltaic microinverter based on couple of two-switch DC-DC flyback converters has been proposed. The investigation of proposed microinverter efficiency was performed.

In the third chapter a new PI controller with a time-varying proportional constant is proposed and a microinverter output current sinus shape tracking system with a developed controller was investigated. The nonlinear distortions of the current were evaluated. The influence of parameters of the microinverter elements on the microinverter efficiency was investigated. The flyback transformer used in the microinverter has been upgraded.

The main results of the dissertation have been published in 7 scientific publications 5 of them have been published in peer-reviewed scientific journals, 2 in conference proceedings. The results were presented at 10 scientific conferences.

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138 p.
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