| In recent years,with the increasing depletion of energy and the increasingly serious circulation pollution problem caused by the use of non renewable fossil energy,the development and utilization of renewable distributed energy has attracted more and more attention.In order to avoid the fluctuations caused by environmental factors when the distributed renewable energy is merged into the DC microgrid,the energy storage system plays an important buffer role in the DC microgrid,and is widely seen as an effective solution to the problem of renewable energy power fluctuations.Among them,the battery energy storage system is the most economical energy storage method for distributed generation system and microgrid energy storage,which can achieve large capacity at low cost.The work is as follows.First of all,the development status of existing energy storage,the technology is introduced in detail,The bidirectional DC-DC converter is introduced and classified.After introducing the basic knowledge structure of DC micro grid,the physical mechanism of circulating current problem between parallel converters in its energy storage system is described.Then the state space average method and small signal method are used for modeling and analyze the bidirectional Boost step-down converter.It lays the foundation for double closed loop design PI controller.Secondly,the traditional droop control is introduced to summarize the basic principle of droop control,and the problems of poor circulating current suppression effect and bus voltage drop existing in the traditional droop control parallel bidirectional converter are also proposed.Aiming at the main problems left by the traditional droop control on the control of bidirectional Boost buck converter,a comprehensively improved droop control circulating current suppression strategy is proposed,The superiority and stability of the improved control strategy are verified by simulation.Then,because bi-directional boost buck converter has typical nonlinear characteristics,sliding mode control theory is introduced to analyze it.Mathematical analysis verifies the internal dynamic stability of bi-directional converter under nonlinear current control.Aiming at the problems of chattering and loop instability suppression in traditional sliding mode control,a sliding mode control strategy based on nonlinear disturbance observer is proposed to estimate and timely compensate the disturbance,When the system load suddenly changes,it can also maintain a good ability to restrain the circulating current under the condition of inconsistent line impedance.Finally,the relevant models are built in MATLAB/Simulink platform,and the simulation comparison verifies the advantages and disadvantages of the proposed strategy and the traditional strategy. |
