A distributed economic control and transition between economic and non-economic operation in islanded microgrids

In islanded microgrids, traditional droop control tends to make the total operating costs higher as the power is distributed by capacity ratios of distributed energy resources (DERs). According to equal increment rate criteria, to minimize the whole expenses, an interesting marginal costs-based economic droop control is proposed in this paper, and the active power can be distributed by identical marginal costs among DERs under economic droop control. If some DERs have arrived at the maximum or minimum power, consensus-based “virtual” controller is applied to make marginal costs still be the same among the rest of DERs. Moreover, distributed secondary frequency controller (DSFC) is proposed to rapidly restore system frequency to the nominal value. As an ancillary service, the whole design can easily realize the transition between economic and non-economic operation only by altering the type of droop control. The above controllers only need to interact with neighbor DERs by sparse communication network, so that eliminating the necessity of a central controller. An islanded microgrid incorporating renewable generators, storage devices and conventional generators are presented to verify the effectiveness of the above controllers. Simulation results show that the proposed controllers can successfully make islanded microgrids realize economic operation and the above transition.