Enhancement of the stability and the transient response of inverter based DG unit in isolated micro-grids

This paper introduces a mathematical model and a voltage/frequency control scheme for inverter interfacing Grid Forming DG (VF) unit. The introduced control scheme utilizes the well understood and optimized dq-frame current control scheme that is used with inverter interfacing Grid Following DG (PQ) units. Minimum modifications are made to the control software to allow grid isolation operation of the DG. The introduced control scheme is characterized by fast disturbance and start up transients rejection, and mitigation of dynamic coupling between control loops and load dynamics. Further control enhancements are introduced by adding frequency regulation loop and dynamic stabilizing network. The whole control scheme is tested using a proposed test system on MATLAB/SIMULINK simulation environment.