  With more and more distributed energy resources (DERs) deployed in Integrated
Energy Systems (IESs), frequency stability challenges the pursuit of
reliability and efficiency. This paper proposes a fully-distributed frequency
control method for load-side DERs, in which the optimality can be guaranteed in
an IES where electricity and heat are coupled. Moreover, the global asymptotic
stability of the closed-loop system is proved and the robustness with respect
to inaccurate coefficients is shown. Case studies demonstrate the effectiveness
of proposed method.
