  In order to address the economical dispatch problem in islanded microgrid,
this letter proposes an optimal criterion and two decentralized
economical-sharing schemes. The criterion is to judge whether global optimal
economical-sharing can be realized via a decentralized manner. On the one hand,
if the system cost functions meet this criterion, the corresponding
decentralized droop method is proposed to achieve the global optimal dispatch.
Otherwise, if the system does not meet this criterion, a modified method to
achieve suboptimal dispatch is presented. The advantages of these methods are
convenient,effective and communication-less.
