| The development of Micro-grid technology led to an increase in the range of distributed energy resources and expansion of network scale,its dynamic behavior was more and more complicated,which increased the difficulty to control the synchronous operation of distributed unit.Frequency synchronization of all the distributed energy resources is an important part of the stability of Micro-grid systems.Only rely on the droop control strategy of Micro-grid system for frequency control is not enough to satisfy the actual demand,which has strict requirements to droop coefficient and is linear-differential control.Therefore,seeking a kind of modeling method which can highlight nonlinear network properties,convenient for describe the relationship between local and global dynamic equilibrium of network,and based on the model,exploring a nonlinear distributed frequency modulation control method has important theoretical significance and application value.This paper describes the relationship between the dynamic behavior of the unit and stable operation of the whole system from a new perspective of complex networks.Based on it,FM control of Micro-grid system is studied.The work tries to establish a model that can characterize the nonlinear network properties of Micro-grid system,design a nonlinear FM control method to improve the ability to frequency regulation and enhance the frequency stability of micro-grid system.Firstly,this paper analyzes the internal relationship between Micro-grid system and Kuramoto model based on the research of the phase coupling oscillator model of the traditional power system.The DER is classified by analyzing the characteristics and manifestations of the DER's inertia in the Micro-grid system,which corresponds to the first-order and second order form of the Kuramoto model.Based on this,the power structure and phase oscillator equations of each DER is studied respectively,and the corresponding Kuramoto model is established,which highlights the dynamic characteristics of each unit oscillator model.Secondly,the types of nodes in the power network are analyzed,and the simplification steps of the Micro-grid network Kron Reduction are established by using the method of graph theory.The Kron simplification process is simulated using the IEEE5 node example.The dynamic characteristics and equivalence of the Micro-grid network model before and after the structural simplification are studied,which provided a solution to determine the effective oscillator number and network node parameters of the Kuramoto model.Finally,the paper researches the relationship between synchronization of network oscillator and frequency synchronization of Micro-grid.The Lyapunov function is constructed by using the energy function of the oscillator.On this basis,using the Lyapunov direct method proposes FM control strategy,which based on the equilibrium point configuration,solved the relationship between traditional frequency droop control must be linear limitation.The paper completed the design of micro frequency control network system.In this article,the parameters characterizing the Micro-grid are simulated based on the comparison between the Kuramoto model and the Micro-grid system model.The results show that the Kuramoto model of the Micro-grid system is established in this paper can correctly describe the actual Micro-grid system.The network structure simplification is simulated by IEEE5 node example.The results show that the network structure is completely equivalent before and after simplification,and the dynamic characteristics of the network are not changed.The proof results of the constructed Lyapunov function demonstrate the rationality of constructing the Lyapunov function with the oscillator energy function.On this basis,the oscillator model and the Micro-grid model are simulated,The simulation results show that the control strategy designed in this paper can respond quickly to frequency disturbance and has better frequency modulation effect. |
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