Research On Hybrid Energy Storage Technology In PV Micro-grid

With economic development, global energy crisis continue to simmer, the development of new energy as an alternative energy has become essential, Solar energy as the most widespread, the cheapest, the most clean energy, more and more countries around the world pay more and more attentions to it. In recent years, the development of photovoltaic industry is very fast, However, PV power output is large impacted by the environment, As more and more photovoltaic cells connected to the grid, When the dramatic changes in light intensity, the PV output power grid fluctuations will cause great impact, Therefore, this paper expanded research on power fluctuations around weaken photovoltaic systems, based on solar photovoltaic hybrid energy storage system, base on PV model and MPPT control method, add battery and super capacitor to system, so a Micro-grid with storage is composed. In this paper, a hybrid energy storage system is designed, this study focus on hybrid energy storage control method, designed a control method which combined fuzzy PI and control frequency, achieve the goal to suppress the fluctuation on PV systems.The object of this paper is PV system with storage, the structure is DC bus structure, the purpose of this paper is to suppress the fluctuations in power output of PV and maintain the voltage of DC bus. According to the characteristics of PV, create a model of the PV, and use this model to test the P-V Feature and Ⅰ-Ⅴ Feature. Then, Studied the three most commonly used method of MPPT control, this paper use Admittance incremental method to realize MPPT, by modulating the duty of switch in Boost circuit to achieve MPPT control. Then research the topology,mathematical models and control methods of battery and super capacitor hybrid energy storage systems, And analysis the capacity of battery and super capacitor.This paper focus on the control strategy of battery and super capacitor hybrid energy storage, According to the battery capacity is large but slow response speed and super capacitor capacity is small but fast response, Design of frequency control strategy, Using a low pass filter to the power fluctuation is divided into two parts:high frequency and low frequency, the low frequency part is absorbed by the battery, the high frequency part is absorbed by super capacitor storage, thus optimizing the charge discharge curves of battery, improve the life of battery. In order to improve the battery curve, this paper designed a variable cutoff frequency low pass filter, the battery and super capacitor can share a certain percentage of current, and the adaptive fuzzy PI control was added, so that, System can adjust its PI parameters automatically. The charge and discharge curves of battery can be more perfect, restrain the power fluctuation will more obvious.This paper establish a PV system with hybrid energy storage, variable illumination experiment and variable load experiment has been done. The results were well verified that the control strategy can well restrain power fluctuation, Finally, analyzed the power balance when PV system was connected to the AC micro-grid by grid connected inverter.