| Though traditional photovoltaic power generation system has been widely concerned for its unique advantages,it has such disadvantages as fluctuation of power generation which caused by instability of illumination.In order to solve those problems to benefit to all human beings,the DC microgrid with energy storage equipments has been widely concerned and studied.In this thesis,with the purpose of smoothing and compensating the output power of PV power generation,improving its working efficiency,achieving the peak shaving and valley filling for power generation and consumption,the PV-Battery DC-microgrid system,which the accumulator is applied as energy storing equipment,is studied.This thesis has been studied from the following aspects:Firstly,the concept,formation and working mode of MG is introduced.Then the basic model is established,and the power flowing of MG is analyzed under grid-connected and off-grid modes.Secondly,the principle and control strategy of PV power generation in MG is researched.On the basis of the principle of photovoltaic power generation,the mathematic model and equivalent circuit of it is established,and the MPPT control strategy is studied.Then,the two-phase two-port bi-directional DC/DC converter is applied to achieve the charge and discharge control on battery.Based on its small signal model,the control strategy of converter is studied.Thirdly,according to the modeling and control strategy research of single-phase PWM full bridge converter,the different working states that include rectifier and inverter are studied.Besides,a soft PLL algorithm,which based on discrete Fourier transform,is designed to solve the problem of multiple zero crossing points in grid voltage which caused by harmonics.Lastly,the simulation model of MG is established in MATLAB/Simulink to verify the correctness of theory.Then the hardware experiment platform of MG system is builded,and the software program is designed.The feasibility of above research is verified by the experiment results. |
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