A Study On The Energy Control Strategy Of Photovoltaic System With Battery Energy Storage

With the rapid development of the photovoltaic(PV) industry in recent years, the present PV generation system becomes a mature and well applied technique, it develops towards to a grid-connected derection instead of stand-alone PV system. But the output power of PV system is vulnerable to the impact of changes in the external environment and exists many uncertainties. As a flexible and stable energy generation system, the PV based on the battery energy storage system(PV-BESS) will be the new hot spots of research and application of the PV industry.This paper presents research on the possibility of employing a battery energy storage method in PV grid-connected power generation system to enhance the performance of its power quality and stability. Based on the survey and analysis of the current research work, this paper did the main research on the problems of PV-BESS development and the energy manage control, aiming at the realization of the practical PV-BESS that can control the generation and manage the whole systems. A mathematic model of battery energy storage system based on equivalent circuit and a photovoltaic based global dynamic mathematical model for PV-BESS grid-connected system are built, and corresponding conrtol strategy is developed to control the output power. Based on these models, a simulation platform of PV-BESS is developed by using Simulink of the Matlab to analyse the power quality and stability.Based on the theoretical analysis, the thesis gave a detailed introduction on the hardware and the software design which take the TMS320F2818as the control core. The architecture and implement of the PV-BESS is presented in this thesis, it proposed a flexible modular structure which composed of PV generation control system, battery energy storage system and system monitor system. Based on the modules design, an energy control system is developed to solve the compatibilities among the modules and software modules are developed on DSP which can perform some functions that hardware can do. This design has properties of reliability and flexibility. And then, an efficient MPPT method for PV-BESS is presented, using the variable step perturbation observation algorithm based on the duty cycle of Boost converter. This control strategy meets system requirements and requires a few numbers of arithmetic operations. In the end, A charge and discharge control strategy for storage battery are suggested, and corresponding protection functions are provided to ensure the performance and the operational life of the batteries and the stability of the whole system.Both the experimental results and the simulation results show that it is flexible and can be well output the power schedulablity and stability.