This thesis proposes an autonomous control curve change method in smart inverters to improve the stability of the point of common coupling (PCC) voltage. As the interconnection and capacity of distributed energy resources (DER) have been increasing to solve the environmental pollution problems. The fluctuation problems on PCC may occur and the stability of grid-connected systems becomes unstable because of increasing DER. A smart inverter is equipped with grid support functions to improve these problems and controls the active power and reactive power according to the control curve. In this thesis, the smart inverter performs the Volt-VAR function which is a typical grid support function. The smart inverter autonomously changes the control curve to improve the stability of PCC voltage. If the PCC voltage is not suppressed within the stable range, the control curve is autonomously changed with a larger slope. The smart inverter maintains the control curve when the PCC voltage is controlled within the stable range. The effectiveness of the proposed autonomously control curve change method is validated by the simulation and experimental results.
