Coordinated Control And Energy Management Of Flexible Interconnection System For AC-DC Multi-distribution Feeder

In recent years,in the face of energy shortage,environmental pollution and rapid economic development.A large number of renewable distributed power sources and energy storage equipment are connected to the grid,and the users have increasingly demanding power supply reliability and power quality.DC grids have attracted more and more attention due to their significant advantages in distributed energy access,increased transmission capacity,improved power reliability and power quality.In order to adapt to the current situation where the AC distribution network is the main distribution system and the DC distribution network is gradually developing,building an interconnected network of the power system that is suitable for the current stage is an important step to realize the Internet of Energy.Aiming at the key problems existing in the power grid at this stage,around the goals of adapting to multi-grid interconnection,improving power supply reliability,and energy management,build an flexible interconnection system of AC-DC multi-distribution system which includes multiple AC-DC grids,distributed power sources,energy storage,and flexible loads.Research on coordinated control and energy management for this system includes coordinated control methods based on DC bus voltage and improved coordinated control methods in terms of coordinated control,as well as day-ahead and intra-day optimization in energy management.The main research work of this thesis is summarized as follows:Based on the characteristics and key issues of the power grid at this stage,and aiming at multi-network interconnection,reliable power supply,and energy management,the flexible interconnection system of AC-DC multi-distribution feeders is constructed,including its functional architecture and system architecture.At the same time,the system topology and the topology of each component were analyzed,explained,and designed,which laid the theoretical foundation and technical framework for the subsequent research and construction of AC / DC multi-distribution feeder flexible interconnection system.In addition,around the reliability and economic requirements of AC / DC multi-distribution feeder flexible interconnection system,combined with the advantages of multi-agent control autonomy and communicability,this thesis proposes a multi-agent hierarchical control based on multiple time scales.System control is divided into three levels with different time scales and different control objectives to achieve system energy management and coordinated control.Aiming at achieving the energy management of the AC-DC multi-distribution feeder flexible interconnection system system,and considering the error of light and load prediction,a two-stage energy management strategy is proposed.This strategy divides the DC bus voltage into different sections.In different voltage sections,each power conversion unit has different control strategies.Each power conversion unit can perform modal switching by detecting the local DC voltage signal.Taking a typical AC-DC multi-distribution feeder flexible interconnection system as an example,the proposed coordinated control strategy is simulated.The simulation results show that this strategy can realize the coordinated control of each unit in the AC-DC multi-distribution feeder flexible interconnection system.Secondly,in view of the problems of insufficient droop control performance and DC bus voltage deviation in the above control methods,an adaptive droop control based on the residual power margin and a secondary adjustment for compensating the DC bus voltage offset are proposed.The simulation analysis proves that the above strategy has the effect of enhancing system regulation ability and compensating DC bus voltage.Aiming at realizing energy management of AC / DC multi-distribution feeder flexible interconnection system system,and considering the error of light and load prediction,an energy management strategy based on multiple time scales was proposed.By comprehensively considering the electricity price cost of the power grid,the power generation cost of each device,the charge and discharge cycle life of the energy storage system,demand-side management,the system and various power source-related constraints,an energy management model for AC-DC multi-distribution feeder flexible interconnection system was bulid.The model is divided into day-ahead optimization and intra-day optimization.The day-ahead optimization takes the minimum comprehensive cost as the goal,and obtains the reference value of each power source output and the demand-side management solution.The intra-day optimization method inherits the demand-side management solution,with the goal of the lowest comprehensive cost and the smallest deviation from the previous optimization reference value,and output the output value of each power source.The relevant model is established in the Matlab working environment,and the Gurobi solver is used to solve the problem to verify the effectiveness of the energy management model.