Droop-Free Distributed Control for AC Microgrids With Precisely Regulated Voltage Variance and Admissible Voltage Profile Guarantees

In this paper, we propose a droop-free distributed cooperative control with precisely regulated voltage variance and admissible voltage profile guarantees for AC microgrids. First a distributed voltage variance observer is proposed and proven to be able to converge to global voltage variance using only local measurements and information from neighboring distributed generators (DGs). A droop-free distributed control with average voltage regulator, voltage variance regulator, and relaxed reactive power regulator is then designed and shown to be able to achieve the regulation of average voltage and voltage variance and relaxed reactive power sharing in steady-state. For relaxed reactive power sharing, one special DG that could be a community-owned or utility-owned DG will not participate in reactive power sharing and this flexibility is utilized to regulate the voltage profile. The small-signal stability of the system with the proposed control is evaluated by measurement-based Prony analysis, which can also guide the control parameter selection. It is also shown that the steady-state solution of the proposed control can be obtained by solving a set of nonlinear equations, which allows more efficient evaluation of the control performance under different operating conditions and various controller settings. To validate the performance of the proposed control, extensive real-time simulation studies are performed in OPAL-RT on a four-DG test microgrid.