Distributed Fixed-Time Optimal Active Power Control Of Islanded Microgrids

Microgrid is a small-scale power system comprised of distributed generations,local loads,and energy storage systems,which can operate in either grid-connected mode or islanded mode.Due to the heterogeneity and small-inertia of distributed generator and the polytrope of load,the control and management of microgrid become a challenging problem.The islanded microgrid not only needs to achieve frequency synchronization and voltage stability,but also needs to achieve active and reactive power sharing.Droop control method is widely used to realize decentralized autonomous control of islanded microgrid,but this method leads to the frequency and voltage amplitude deviation and the noneconomic load sharing.In order to achieve the stability and economic operation of microgrid,communication based traditional control strategy uses centralized control structure,which leads to high communication and computing burden,and poor robustness and scalability.To solve aforementioned problems,this thesis presents distributed coordination control schemes based on distributed cooperative control of multi-agent systems,the proposed schemes guarantee that the frequency and voltage amplitude restores to their nominal values,and achieve the economic optimal active power sharing.The main contributions of this thesis are summarized as follows.(1)A distributed fixed-time secondary control scheme is proposed to restore the frequency and voltage to their nominal values.The stability of the proposed scheme is rigorously proved by applying fixed-time Lyapunov theory,the settling time of the proposed scheme exists an upper bound that is independent of the initial conditions,this advantage makes it possible to off-line predesign the settling time according to task requirement.Simulation results verity the effectiveness of the proposed secondary control scheme.(2)A distributed fixed-time economic dispatch algorithm,which maintains supply-demand balance constraint and generation capacity constraints,is proposed based on the equal incremental cost criterion.The fixed-time convergence and optimality for the proposed algorithm is rigorously proved by applying fixed-time Lyapunov stability theory.Simulation results show the effectiveness and superiority of the proposed economic dispatch algorithm.(3)Regarding to the optimal active power control problem,this thesis presents three distributed optimal active power control schemes based on the distributed fixed-time secondary control scheme and the distributed fixed-time economic dispatch algorithm.The first distributed control scheme is based on the incremental cost droop,the second distributed control scheme is based on the hierarchical control,the third distributed control scheme direct optimizes the parameters of the droop controller.Simulation results show the effectiveness of the proposed schemes.