Research On Cooperative Control And Load Distribution Of Distributed Units In DC Microgrid

In view of the global energy shortage and climate pollution,the vigorous development of renewable energy has become an effective way that people have found.As a new power system that can flexibly consume renewable energy and realize the integration of supply and storage,microgrid has been extensively developed in recent years,and as a powerful supply for smart grids,it may continue to be paid more attention in the future.DC microgrid has become popular in the research of microgrid because of there is no reactive power balance and harmonic pollution.At the same time,DC microgrid can fully realize the efficient use of wind energy,solar energy and other renewable energy,and can directly accept energy storage,DC equipment such as electric vehicles.Many scholars at home and abroad are interested in DC microgrid.This paper conducts related researches on the cooperative control and load distribution of distributed units in DC microgrid.The main contents include:1.Based on the analysis and summary of the research carried out by domestic and foreign scholars in the field of microgrid,the RTDS experimental platform is used to complete the model building of the DC microgrid,including the modeling of photovoltaic systems and battery cells.According to the principle of photovoltaic power generation,the output characteristics of the photovoltaic array are analyzed,and the charging and discharging characteristics and control of the battery are introduced.2.For the independent operation of DC microgrid,due to the objective existence of line impedance,traditional droop control cannot realize the accurate load power distribution of distributed generations(DGs).In order to improve the efficiency of DGs,an improved droop control strategy that takes into account the line impedance is proposed.The stable operation of the system is realized by designing a power distribution controller and a stable operation controller.3.With the increasing complexity of the DC microgrid network structure,the existence of mismatched local loads may also affect the load distribution accuracy of the system.Therefore,a hierarchical coordinated control strategy for DC microgrid based on adaptive compensation is proposed.Sample-and-hold is introduced in both the load distribution stage and the voltage control stage to adaptively adjust the droop curve to eliminate the influence of mismatched line impedance and local load.At the same time,based on the idea of optimizing the pinning control,the compensation coefficient is introduced,and the bus voltage can be restored to the ideal level only by using the local local electrical information.4.The peak shaving and valley filling of the island DC microgrid system may require energy storage system.The distributed energy storage units(DESUs)use its own charging and discharging to balance the power supply and demand within the microgrid.However,the actual system may include the problem of mismatched parameters between line impedance and local load,which can directly affect the state of charge and load distribution of the DESU.In order to avoid excessive charging/discharging of some energy storage units,this paper proposes an optimized state-of-charge balance control strategy considering mismatched parameters.For the energy storage system,a self-adjusting virtual impedance on the basis of the traditional virtual impedance is introduced,the problem of mismatched parameters is overcomed,and the So C balance and accurate load distribution of DESUs is realized.Finally,the source-load-storage coordination and stability of the DC microgrid system is ensured.