Research Of The Isolated Bi-directional Cuk Converter In PV Power System

With the rapid development of the human society, the traditional energy consuming and the resulting environmental pollution problems are becoming more and more serious. In order to cope with the global energy and environmental crisis, photovoltaic power generation and other new energy industries have obtained the considerable development in recent decades. Solar energy has the advantages of pollution-free, widely distributed and rich reserves. It is an ideal substitute of traditional energy. In the photovoltaic power generation system, the bi-directional DC/DC converter is used between the DC bus and battery or other energy storage devices as the bridge of bi-directional energy transfer to manage the system energy by the way of charging and discharging. So, it is an very important part of the photovoltaic power generation system.In this paper, the application of the isolated bi-directional Cuk converter in photovoltaic power generation system is studied thoroughly. Firstly, this paper gives a brief introduction of the basic structure and characteristics of photovoltaic power generation system and emphatically analyzes its energy management and scheduling strategy. And then the bi-directional DC/DC converter and its specific application in photovoltaic power generation system are comprehensively introduced. Secondly, a detailed analysis of the topological structure and working principle of isolated bi-directional Cuk converter is given, and according to the characteristics in different operation modes of the converter, different closed-loop control strategies are chosen. When the converter operates in buck mode with the relatively small duty ratio, the traditional PI control strategy is used. But when the converter operates in boost mode with the relatively big duty ratio, the system will be in a strong nonlinear state that the traditional PI control strategy is not suitable for its closed-loop control. So, through the comparison and analysis among the fuzzy control and other existing control strategies, an improved PI control strategy which is simple and reliable is designed and used for the closed-loop control in the boost mode. And the system simulation model is built based on the simulation software MATLAB. By the simulation results, the correctness of the system design scheme is verified. Finally, the detailed procedure of the hardware design and the software design are given, and the experimental platform is built based on the hardware and software.On the above basis, a series of debugging and experiment works are carried out. The experimental data and waveforms verify the feasibility and correctness of the system scheme again.