The Research Of Control Strategy And Frequency Stability On Micro-Grid

With the rapid development of human society and power system,especially the increasing of power load,the disadvantages of the centralized grid are gradually exposed.On the other hand,the social reality of limited fossil energy reserves and environmental pollution has caused people to pay attention to the distributed generation technology.However,distributed generation also has many defects so that it is difficult to play its inherent advantages in solving these problems.Under this background,the concept of Micro-grid came into being.Micro-grid is a single controllable system,consisting on distributed power,power load,energy storage and control module.It can be operated on many modes,but no matter what kind of operation mode,it is necessary to control the system precisely.In addition,due to the Micro-grid own structure,its inertia is small so it is easy to be disturbed,so it is necessary to analyze the stability of the Micro-grid.This paper begins with the research background and significance,illustrating the control method of interface inverter,control strategy and stability analysis etc;then establishes the mathematical model of three-phase inverter in two coordinates,and elaborates eigenvalue analysis method of the small signal stability analysis.Specific work as follows:(1)This paper analyzes the power transmission characteristics of distributed power sources and droop controllers,then designs a voltage and current loop controller which based on its equivalent impedance’s characteristic.The controller can make resistance impedance change to inductance impedance by changing the parameters so that droop control can be used successfully.At the same time the problems of voltage and frequency regulation during isolated operation can be solved,and the switching between isolated and grid connected operation with the controller is not affected by control method.At last,this paper does some simulation in three operation modes and analyzes its results deeply.Simulation results show that the system can realize smooth transition between the various operation modes with this controller.(2)This paper analyzes the system stability in a variety of operating modes and builds the small signal state space model during isolated operation,then gets the characteristic value by solving the state matrix eigenvalues of the mode,afterwards the system frequency stability is judged by using the first method of Lyapunov.Through analyzing the simulation results,we can draw the conclusion that system stability will be affected when certain parameters change in Micro-grid.