| With the rapid development of the global economy, demand for energy increases dramatically and leads to the gradual exhaust of the traditional fossil energy. Renewable energy as an alternative to fossil fuels has attached more and more attention. Distributed generation is an important form of the utilization of renewable energy, which has the intermittent and random feature for power output, so large-scale grid-connected is bound to have an impact and influence on the security and stability of the grid. The micro-grid develops on the basis of distributed generation, and it not only can accept a large number of renewable energy to alleviate the energy shortage and environmental crisis, but also can help improve power supply reliability and increase the capacity of the power supply system. To meet the need of large-scale distributed generation access to micro-grid, the study of how to control the energy storage device, distributed power and converter with the changes of the loaded power and network can we make sure that the micro-grid could meet the requirements of power quality under different operating modes is particularly important. This paper focus on research and design of photovoltaic and battery energy storage hybrid micro-grid (PV-BESS), and the details are as follows:(1) A feasible method of modeling the photovoltaic cells suitable for engineering simulation application is presented. In this paper, we choose the perturbation and observation as the MPPT control algorithm to calculate the circuit parameters. The model of photovoltaic power system is built in Matlab/Simulink. The simulation is performed under different temperature and light intensity, and simulation result shows that the simulation model and control algorithm can reflect accurately the changes of environment temperature and light intensity.(2) This paper introduces the principle and advantage of lithium iron phosphate battery for energy storage and establishes an equivalent circuit mode, then the quantitative calculation on battery capacity is carried out. The working principle of Buck/Boost bidirectional converter is analyzed and derive small-signal mathematical model is designed. Voltage of the outer ring current inner bicyclic control method was based on the small signal transfer function. Building a simulation model of the battery energy storage system in Matlab/Simulink, simulation result demonstrates that the control strategy is effective.(3) Micro-grid operation mode and control strategy are analyzed, and the two control strategies of local level and system level are reported in detail. On that basis, the coordinated control strategy which is applied to the PV-BESS hybrid micro-grid is proposed. The model of a PV-BESS hybrid micro-grid is built in Matlab/Simulink. The simulation results of different cases in grid-connected mode, islanded mode and mode change are analyzed. The result shows that, the ability of the wonderful dynamic response of the PV-BESS system will be observed, when the external conditions, load power and the network structure changes. Meaning that it can meet the requirements of the micro-grid power quality. The result also verities the validity of coordinated control strategy which is applied to the PV-BESS hybrid micro-grid, and provides a theoretical basis for the experiment.(4) Experimental platform of a PV-BESS hybrid micro-grid based on dSPACE1006system is built. The build of hardware circuit and the selection of device are completed. The controlling part of dSPACE1006system including the signal acquisition and processing circuit, main controller, software protection, Control Desk and PWM signal generator are designed. The experiments in different cases of grid-connected mode and islanded mode are carried out in a low-pressure environment. Experiment results show that the main circuit designed and its control strategy of the system can maintain stable operation in grid-connected mode and islanded mode. |
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