Research On Stability Optimization Of Stand-alone Photovoltaic System Based On Hybrid Energy Storage

Solar energy is of the advantages of pollution-free and rich reserves, and it is an ideal renewable energy. Photovoltaic power has gradually become the typical representative of renewable energy in the solution of increasingly serious energy and environment problems. However, the photovoltaic generation system can be affected easily by external factors and has the defect of intermittency, randomness and fluctuation. Due to these, the photovoltaic generation system should be combined with an energy storage system for ensuring power stability in it. The hybrid energy storage system is consisted of battery and super-capacitor, and thus it can take the advantage of the high energy density of battery and that of the high power density of super-capacitor. This allows it to be suitable for the stand-alone photovoltaic system with the requirement for stability.In the stand-alone photovoltaic system combined with the hybrid energy storage, the connections between the DC bus and PV as well as between the DC bus and the hybrid energy storage system are performed via DC/DC converters, which play an important role in energy management, stability and disturbance rejection of the stand-alone photovoltaic system.In this dissertation, the effect of Cuk converter on the optimization for the power stability in the stand-alone photovoltaic system including the hybrid energy storage has been studied.Firstly, an introduction is presented for the appearance and development of the photovoltaic power system with the hybrid energy storage, including the element model and topology structure of this system. In addition, the topology structure and the principle of Cuk converter are described in detail, and the four kinds of running mode of the system and the control strategy of the corresponding DC/DC converters are analyzed.On the basis of the above, two kinds of simulation models of the system are structured by means of the simulation software MATLAB and using the Simulink. The two modes use Buck/Boost converter and Cuk converter, respectively. Following these, the comparison between the performance indexes for the system using Buck/Boost converter and for that using Cuk converter when both the environment factors vary and the switch of the load occurs has been done. The performance indexes include stability of the system bus, running status of converter and power fluctuation of the load. The comparison shows the excellence of Cuk converter for the optimization of the power stability.Finally, for suppressing the electromagnetic interference due to the operation of Cuk converter, the RCD buffer circuit is selected in this study based on the analysis on the high-frequency characteristics of Cuk converter and the coupling route of the conducted interference. This use of the RCD buffer circuit contributes to further optimization of the power stability.