Research On Modeling And Control Of Switched-Inductor Quasi-Z-Source Grid-Connected System

With the gradual depletion of traditional fossil energy sources and the gradual lowering prices of new energy sources, new energy sources would probably replace the traditional sources of energy. The Photovoltaic power generation is least affected by regions and is convenient to use, so that it has received more and more attention. This paper proposes the sL-qZSI topologies, gives the dynamic model of the topologies and designs the control principle. In the end, this paper detailiy designes the experimental device of the sL-qZSI grid-connected topology.Chapter 1 introduces the backgrounds and practical significance of this study, and provides key technologies of photovoltaic grid-connected system which include MPPT technology, grid-connecting technology and anti-islangding technology et,al. After that, this chapter gives four topologies of grid-connected photovoltaic system and verifies the developing history of sL-qZSI. In the end, a general description of this article is gived.Chapter 2 gives a detailed analysis of three topologies of sL-qZSI in order to get the method of analyzing and choosing topologies. Firstly,it gives the boost factor G of the three topologies under the same shoot-through duty ratio and verifies the conclusion through the simulation. Secondly,this chapter compares the current stress and the voltage stress of the capacitors and the inductors in this inverter. In the end the conclusions are verified by the simulation.Chapter 3 deduces a small signal model of the sL-qZSI system. Firstly, the signal flow graph is derived by the state space averaging method so that we can get the small signal transfer function GVd(s) and Gvi(s). Secondly, these transfer functions are detailly analyzed by pole-zero plots, sinulations and experiments. The results are that only Gvd(s) has a right half plane zero-point and that system’s dynamic performance is affected largely by the capacitors and inductors. Finally, we choose components and design the control scheme by these conclusions.Chapter 4 then introduces the overall control scheme of the system. Firstly the photovoltaic cells is modeled. After that, various MPPT algorithms are introduced and then the specific scheme of realizing MPPT is gived. Furthermore, the control method that can make system connected to the grid and anti islanding effect is proposed. In the end, we study a brand new control scheme that can be applied to a flat system.Chapter 5 proposes the whole process of building the experimental device. The overall technical program is gived firstly. And then the parameters of the power devices is deduced according to the technical requirements. In order to show the complete process of making the experimental device, this chapter gives the measurement and control circuits besides the software program. Finally it describes the experimental schemes and results from the initial stage to the final one.Chapter 6 makes a summary and outlook; it provides an overview of the achievements of this project and the research content pending further study.