Adaptive synchronous reference frame virtual impedance controller for accurate power sharing in islanded ac-microgrids: A faster alternative to the conventional droop control

The proportional power sharing has been identified as an important issue to guarantee reliability on the operation of low voltage AC-Microgrids. However, inaccurate reactive power sharing in scenarios with line impedance mismatches, and slow transient response remain important limitations of most of the conventional power sharing controllers. In this context, an improved method for power sharing control based on a synchronous reference frame virtual impedance primary controller and a decentralized adaptive virtual impedance algorithm is proposed. This strategy achieves an accurate active and reactive power sharing performance, in spite of the mismatch of the feeder impedances values, and without an accurate knowledge of the line parameters. Additionally, a faster response in comparison with the conventional droop control approaches are achieved without centralized communication requirements, using distributed communications between neighbor generation units. Conditions of the virtual impedance parameters to guarantee an accurate power sharing performance are presented, a cyber-physical model of the control strategy is developed, and the impacts of constant communication time delays on the power sharing performance are discussed. Numerical electromagnetic-transient simulations are performed to compare the performance of the conventional droop control approach with the proposed strategy, as well as, to evaluate the impact of communication delays.