Single-phase single-stage grid-connected converters using high frequency virtually grounded technique

Abstract

In the modern power grid, renewable energy has become one kind of major energy resources in the world as it is environmentally friendly and sustainable. To effectively convert the power between the ac grid and different energy sources, power electronic converters are required. They act as an interface to establish a connection between the renewable energy source and the utility grid or microgrid network. Meanwhile, the power converters are also the power interface between different electronic appliances and the ac grid. This thesis aims to research on high frequency virtually grounded technique and to develop a new set of converter topology that is with high efficiency and low leakage current performance. Different kinds of common-mode migration technique are studied in terms of system performance. By using the theory of high frequency virtually grounded technique as a foundation, the new series of converter topology family is established. According to the needs in different applications, several types of converters have been developed which is high efficiency and low leakage current. In the new converter family, a bridgeless power factor correction rectifier is studied for the general boost-type power factor correction circuit. For applications with reactive power demand, a bidirectional voltage source converter is introduced. In addition, a buck-boost-type bridgeless power factor corrector is proposed for those wide output voltage range grid-connected converter applications. Lastly, a buck-boost-type inverter is discussed in this thesis for those high efficiency wide input voltage range inverter systems. An in-depth study on the grid-connected converter topologies is provided which includes the detailed operation principles and the corresponding system stability analysis. All of the described topologies are experimentally verified which shows good agreement with the theoretical knowledge. Moreover, the performance of those converters is measured based on industrial requirements in terms of efficiency, total harmonic distortion, power factor and leakage current.