Control Of Microgrid System And Parameter Identification Of Load Excitation

With the rapid development of science,technology and industrial technology,the global energy crisis is increasingly serious,the development and utilization of new energy has become an inevitable choice and development trend,micro power grid as an effective supplement to the large power grid and the effective use of distributed energy form,its development will be unstoppable.With the wide application of micro-grid,its related control and system stability and reliability research has been paid attention to.This paper focuses on the two aspects of smooth switching of control mode in grid-connected operation state and parameter identification of micro-grid system in off-grid operation state.The main research contents of this paper are as follows:(1)The research background of micro-grid is introduced,including its generation,characteristics and development;the research status of virtual synchronous generator control and parameter identification is analyzed,and the research focus of this paper is proposed.(2)The conventional control modes of the micro-grid inverter are analyzed: PQ control,V/f control,and droop control.The control mode and implementation of the virtual synchronous generator are mainly discussed.The theoretical analysis of the control characteristics based on VSG,including power frequency adjustment characteristics and stability,and the correctness of the theoretical analysis are verified by simulation,which provides a theoretical basis for the smooth switching of the control mode and the parameter identification of the micro-grid system.(3)In view of the existing literature,there are few studies on the smooth switching of control modes under grid-connected conditions,and a smooth switching method based on VSG and PQ control is proposed,which is applicable to the situation that the control strategy should be changed according to the actual conditions during grid-connection operation.In this paper,by controlling the current inner loop command value and the phase of the modulated wave,the two control modes are smoothly switched,and the effectiveness of the proposed method is verified by simulation and experiment.(4)The micro-grid system was simplified and the equivalent model under off-grid operation was obtained.Aiming at the step disturbance mode of power instruction value and load,an online identification method of piecewise forgetting factor recursive leastsquares is proposed to improve the steady-state performance and dynamic response performance of the identification results,and compared with nonlinear curve fitting least squares offline identification method.Then,the identified parameters are used for secondary adjustment of frequency and voltage to optimize the control of the original VSG,and the set value of power frequency control loop PI regulator is obtained according to the design theory of typical type II system controller.Finally,the effectiveness of the proposed identification method is verified by simulation,and the results of the two disturbance identification are compared.At the same time,the simulation verifies the effectiveness of the secondary adjustment control.