Research On Voltage Hierarchical Control Method Of Photovoltaic Storage DC Microgrid

The stability of the common DC bus is an important index to evaluate the stability of the optical storage system.The coordinated control of each network device is an important way to maintain the voltage stability of the bus.However,this control is challenged by the intermittenity,randomness and nonlinearity of the distributed power supply.Therefore,this paper takes a typical optical storage DC microgrid containing photovoltaic,energy storage,grid-connected interface circuit and constant power load as the research object.Based on the analysis of the system impedance model,a distributed mode switching method is studied to stabilize the DC bus voltage.Firstly,the equivalent impedance model of the system is established,and the mechanism of the influence of constant power load on the system stability is studied.Then the influence characteristics of controller parameters and hardware parameters on the equivalent impedance of each device in the system are analyzed by the impedance stability criterion.Secondly,based on the characteristics of each device in the microgrid,the voltage hierarchical control strategy is used to divide the working interval of each network device,and the corresponding working mode of each device in different sections is set to realize the coordinated and stable operation of the distributed control of the microgrid system.The problem of frequent switching of working mode caused by the change of the working interval of the device caused by the voltage fluctuation of the DC bus is analyzed.In addition,the traditional methods of working mode switching are analyzed,and the existing problems of applying low-pass filtering method,hysteresis comparison method and Kalman filtering method in DC bus voltage control are summarized,especially the problem that the designed filter is difficult to take into account both dynamic and static indicators.Therefore,an active weighted aggregation filtering method is proposed.By dynamically adjusting the weight coefficient,the method dynamically balances the effect of large time scale filtering.and small time scale filter,and gives consideration to the frequent switching of operating modes of distributed devices caused by condition misjudgment under boundary conditions.All the experimental conditions of hardware and software used in the networking converter are set up,including the photovoltaic maximum power tracker,the energy storage DC-DC converter and the grid-connected interface circuit,and the networking experiment is carried out.The optimization method is applied to the controller of each network device,and the correctness and effectiveness of the voltage stratification control strategy and the active weighted aggregation filtering method are verified by simulation and experiment under different working conditions and load changes.