On design of power sharing for VSC-based islanded AC microgrids: An adaptive MIMO controller equipped with a predictor

In an AC microgrid, the active/reactive power is usually shared among its distributed generators (DGs) based on the frequency-active power (F-P$F-P$) droop and the voltage-reactive power (V-Q$V-Q$) droop. By increasing the resistant/inductance ratio (R/X$R/X$) of feeder lines; however, adverse effects of interactions between these two control loops are intensified. In this paper, an adaptive multi-input multi-output (MIMO) current control structure is proposed to tackle this problem in AC microgrids with arbitrary numbers of DGs in the primary control level. A deep analysis based on the relative gain array (RGA) matrix and the diagonal dominance concept is provided to systematically design MIMO controllers. The proposed technique is based on the Lyapunov's stability theory, and the asymptotic stability of the whole microgrid is guaranteed. For each DG, the suggested design procedure is started by defining a model reference in which the desired control objectives, including the settling time and the steady-state error, are considered. Then, a feedback-feedforward controller is established where its gains are adaptively tuned by some rules derived from a Lyapunov function. Moreover, a predictor is used to estimate the adverse effects of other DGs which are taken into account as external disturbances during the design process of the adaptive controller. By considering some realistic scenarios through time-domain simulations in MATLAB/SIMULINK, it is shown that the proposed strategy can be successfully used to solve the power sharing problem in AC microgrids. A MIMO model reference adaptive controller is designed for AC microgrids to solve the problem of power sharing among their DGs. Based on the estimation of the interactions among the control loops, their adverse effects are systematically attenuated.image