Study Of DC Micro-grid Bus Voltage Stability Under Perturbation Of Constant Power Load

With the depletion of fossil fuels and the growing problem of environmental pollution,people urgently need new energy sources as alternative energy sources or supplementary energy sources.Distributed generation represented by wind power generation and solar power generation has been applied on a large scale due to its clean and renewable advantages.Therefore,the new energy grid-connected form is also slowly transitioning from a centralized grid to a distributed grid.However,due to the intermittent,volatile,and uncontrollable characteristics of these grid-connected methods,modern new energy sources are increasingly connected to the grid through the form of micro-grids.The initial phase of grid-connected micro-grids for distributed generation is mainly based on AC micro-grids.With the increase of DC equipment at the source and load side,DC micro-grids are getting more and more attention.Compared to AC micro-grids,DC micro-grids have the advantages of simpler control,higher power quality,lower system losses,and the ability to be used in more applications,enabling the full benefit of micro-grids.At present,the research of DC micro-grid mainly focuses on five aspects:topology structure,optimization planning,operation control,protection technology and communication system.With the increasing proportion of constant power loads in DC micro-grids,their influence on bus voltage stability is also increasing.The voltage of the DC micro-grid is the only standard to measure the stability of the system.Therefore,this paper mainly studies the influence of the constant power load on the bus voltage stability.This paper first analyzes the characteristics of constant power load,and then analyzes the phenomenon and mechanism of system instability caused by constant power load.Finally,the typical topology of DC micro-grid is selected,and large signal modeling is performed by means of state averaging method,and in Matlab/Simulink Build a DC micro-grid model in a simulation environment.This paper presents a composite controller applied to the source DC/DC converter.The composite controller is designed based on a nonlinear disturbance observer and recursive backstepping algorithm.The design flow of the composite controller is to first transform the system dynamic equation into Brunovsky's standard form through differential isomorphism coordinate transformation;then use a nonlinear disturbance observer to estimate the load power variation in the fast dynamic response,and improve it as feed-forward compensation.The accuracy of the output voltage regulation;the final use of recursive backstepping algorithm,in line with the stability criteria to ensure the stability of large signals,the design of the nonlinear controller.For the composite controller proposed in this paper,a reasonable controller parameter is designed by simulating the four controller parameters.Aiming at the compound controller under this parameter,the simulation study was conducted under three increasingly harsh conditions:resistive load and constant power load,purely constant power load disturbance,and large changes in DC bus reference voltage.The simulation results show that under the three conditions,the composite controller has a faster response speed,and can meet the large signal stability of the system under large disturbances.By investigating the power limit of the system under different disturbance amplitudes,the simulation results show that the composite controller has a larger stability domain and better stability.Compared with the traditional dual PI loop controller under the above three conditions,the simulation results verify that the composite controller has better voltage stability than the traditional dual PI loop controller at the same response speed.The superiority of this compound controller.