Research On Operation Control Strategy Of Island DC Micro-grid Based On Accurate Feedback Linearization Sliding Mode

With the progress and development of human society,the demand for energy has been also increasing.The accelerated consumption of traditional energy has brought about unavoidable environmental problems.Under the dual pressures of energy and the environment,renewable distributed energy source has received a lot of attention.If the distributed generation is connected to the grid without control,it will pose a great potential threat to the stable operation of the grid,so Micro-grid comes into existence as the situation requires.Micro-grid can be divided into three types: AC,DC,AC-DC hybrid.At present,the Micro-grid mainly exists in the form of AC,but with the popularization of DC loads and the development of DC distributed generation,DC Micro-grid has a promising future.In view of this situation,based on the control of distributed generation and energy storage unit,the operation control strategy of DC Micro-grid island is studied in this paper.First of all,the basic structure of DC Micro-grid is introduced in this paper.The photovoltaic cell is selected to represent for the distributed generation,and the lead-acid battery is used as energy storage unit.Based on the analysis of the mathematical model of photovoltaic cell,a practical engineering model is built,and the operation characteristics of photovoltaic cell are studied by simulation.Then,on the basis of the engineering model of photovoltaic cell,the maximum power point tracking(MPPT)is implemented with the improved conductance increment method.The simulation results show that the algorithm is effective and rapid when the light intensity and temperature are changed.Furthermore the general model and the third-order dynamic model of the battery are introduced,and the two working modes of the Buck-Boost bidirectional converter between the battery and the DC bus are analyzed in detail.Secondly,for the constant voltage control mode of photovoltaic cell,a sliding mode controller is designed on accurate feedback linearization.Simulation results show that the sliding mode controller designed has better robustness and rapidness than the PI controller when the external parameters are changed.The charge and discharge model of the battery is built on the basis of the lead-acid battery model in Matlab/simulink.Buck-Boost converter operates in the complementary conduction mode.A controller is designed using the backstep sliding mode method based on the accurate feedback linearization.The superiority of the controller compared with the PI controller is verified by simulation,which is more stable and fast during charging and discharging control.Finally,an island DC Micro-grid system is built.Based on the power balance equation,the operation mode of the island DC Micro-grid is divided into three major modes: normaloperation,photovoltaic constant voltage,and load shedding.The sliding mode controller is used instead of the PI controller.In different operation modes,the controller runs the corresponding working mode.The correctness of the proposed operation strategy is verified by simulation in the Matlab/simulink.The operation strategy combined with the improved sliding mode controller can make the system run steadily.The system can switch between different modes smoothly and quickly,the goal of stabilizing the DC bus voltage is achieved.