Research On Synchronization Stability Optimization And Control Of Heterogeneous Microgrids Based On Complex Network Theory

With the increasing depletion of traditional coal,petroleum,and other fossil fuel resources,the development of microgrids not only promotes the transformation of the traditional energy structure but also plays an important role in the development of smart grids.Different from centralized and large-capacity thermal power plants,the AC microgrid system requires a large-scale installation to ensure effective output power due to its low energy density and small single-unit capacity.Under the islanded islanded mode of large grid separation.However,as the number of distributed power generation units increases,the dynamic characteristics of the entire microgrid system will present a high-order and multidimensional “dimensional disaster” situation.Therefore,the traditional analysis and control methods of single or multiple distributed power generation units are difficult to be extended to the related research of large-scale distributed power generation and based on the three-tier control architecture of the microgrid,the traditional control methods will also No longer applicable.The complex network and multi-agent theory provide favorable analysis tools for solving large-scale power network system modeling and control.Due to the different dynamic models and parameters of different types of units in the microgrid,this article focuses on the heterogeneous AC islanded microgrid system,focusing on the relationship between topology and synchronizability analysis,and the application of distributed cooperative control in microgrid control Research on two aspects.The main research contents include:The topological structure plays a vital role in the overall synchronizability of the islanded microgrid,and there is still a lack of sufficient theoretical research on the impact of changes in the topology on the synchronization of large-scale microgrids.In response to this situation,based on the equilibrium point of the nonlinear system and the Moore-Penrose generalized inverse theory,this paper derives a new simple criterion for the synchronizability of the islanded AC microgrid.And then this paper theoretically analyzes the influence of topology change on synchronization ability.Based on the algebraic graph theory and the linear change theory,the synchronizability performance of islanded AC microgrids under different topological structures is compared and analyzed,and a new topological structure is proposed.The results showed that the synchronization performance of conventional topologies is more restricted in large-scale case,the newly proposed topology can significantly enhance the ability to synchronize the microgrid can be effectively prevented in the respective Braess' s paradox appears in the process of topological transformation.It provides a theoretical basis for the topology design of the microgrid and the judgment method of synchronizability.The economic distribution problem of a microgrid is often realized in its tertiary control layer.Due to the difference in time scale,the hierarchical control often has hysteresis,which leads to reduced economic efficiency.Most of the existing control strategies consider leader nodes or require global information,and most of them do not consider various local constraints in the microgrid,so they cannot reflect the actual operating scenarios.Aiming at the overall economic efficiency of the islanded AC microgrid energy storage unit,this paper proposes a new leaderless distributed cooperative control algorithm based on multi-agent system.This method is completely distributed and can cooperate with the inverter to eliminate the steady-state frequency deviation and achieve the optimal overall system economy.In addition,the control strategy is designed through local constraints on the charge and discharge rate,state of charge,and charge and discharge cycle,so as to make it fit the actual operating scenario.The equilibrium point theory is used to prove the global asymptotic stability condition of the proposed controller.Finally,simulation experiments verify the effectiveness of the scheme in solving the problems of frequency synchronization and economic allocation.When large-scale distributed energy is integrated into the microgrid,the synchronization of the system will become more difficult,and the communication and calculation costs required for the control process will greatly increase.In islanded mode,the time for the frequency to restore to the rated value and the transient peak deviation of the frequency when the microgrid system responds to load changes and other disturbances are of great significance to the safe operation of the system.At present,the secondary control of islanded microgrid usually only pays attention to the steadystate of frequency or voltage.Aiming at the problem of frequency synchronization rate,this paper derives the explicit synchronization rate expression based on the theory of nonlinear system stability and obtains it based on linear programming theory.The optimal conditions for the synchronization rate are shown.On this basis,this paper proposes a distributed cooperative event-triggered control strategy,which can eliminate the steady-state frequency deviation of the microgrid and maximize the synchronization rate.In order to reduce the burden of communication and calculation,this paper also provides an event-triggered mechanism,so that each unit only needs to update its control input based on the discrete information of its single neighbor node,thereby greatly reducing the communication cost.The Lyapunov method is used to prove the stability of the control system under the event-triggered condition,and the lower limit of the event interval is analyzed to avoid the Zeno phenomenon.Finally,simulation experiments verify the effectiveness of the proposed strategy.The energy storage system plays a vital role in the safe and stable operation of the microgrid.The reasonable control of its state of charge and charging and discharging power can extend the service life of the storage battery.In order to accurately,quickly,and robustly control the state of charge and charge and discharge power,most of the existing control strategies use finite time methods.However,the convergence time of the control system is often related to the initial state,which leads to the estimation of the convergence time tends to conservative.In response to this situation,this paper proposes a distributed cooperative improved finite-time control algorithm.The control algorithm can cooperate with the energy storage unit to eliminate the steady-state deviation of the system frequency,and at the same time solve the problem of the state of charge balancing.The Lyapunov method and homogeneous approximation theory are used to prove the stability of the control algorithm,which ensures the accelerated convergence in a stable time that does not depend on the initial conditions.On this basis,an event-triggered communication mechanism that only relies on discrete information and can avoid Zeno behavior is designed,which significantly reduces the communication burden.In addition,by imposing realistic local constraints to implement the control protocol,the service life of the battery is further improved.