Research On Control Strategy Of Three-phase Inverter For Low Voltage

With the development of distributed power supply,microgrid came into being.As the power electronic interface for distributed power access to microgrid,the control method of the inverter is very important for the stable operation of the microgrid.In this paper,three-phase low-voltage civil microgrid inverter is studied,which is difficult to be used in rural areas without electricity,farms,islands,vacation homes etc,where the grid is difficult to extend.In view of problems of the voltage instability caused by nonlinear load perturbation and filtering parameter perturbation in islanding operation and the voltage buffeting caused by the failure to meet the fastness in connected operation,a control strategy is studiedFirstly,according to the resistive output impedance of the microgrid in low-voltage operation,a new droop control strategy is studied,which is contrary to the traditional droop control.The power flow is analyzed,the delay caused by the filter in the system is considered,and the new droop control algorithm is analyzed by small signal,which indicates that appropriate selection of coefficients n_d and m_d,and a good system performance can be obtained.Secondly,in view of the nonlinear load perturbation and filtering parameter perturbation in islanding operation,an adaptive sliding mode control strategy is studied.The three-order sliding mode surface and adaptive laws for switching gain and filter parameters are designed,and the stability of the system is analyzed.The control system is simulated by MATLAB,the simulation results verified that the adaptive sliding mode control strategy has higher robustness.Thirdly,in view of the requirement of fastness in connected operation,a finite set model predictive current control strategy is studied.According to the relationship between inverter switching state and output voltage synthesis vector,and the current dynamic equation for output current of three-phase grid-connected inverter in the ab coordinate system,the predictive model of discrete state space is obtained.The control system is simulated by MATLAB,the simulation results verified that fast trackability of output current of grid-connected inverter to reference current.Finally,the control strategy of this paper is summarized and the next research work is put forward.