  Integrated energy systems (IESs), in which various energy flows are
interconnected and coordinated to release potential flexibility for more
efficient and secure operation, have drawn increasing attention in recent
years. In this article, an integrated energy management system (IEMS) that
performs online analysis and optimization on coupling energy flows in an IES is
comprehensively introduced. From the theory perspective, an energy circuit
method (ECM) that models natural gas networks and heating networks in the
frequency domain is discussed. This method extends the electric circuit
modeling of power systems to IESs and enables the IEMS to manage large-scale
IESs. From the implementation perspective, the architecture design and function
development of the IEMS are presented. Tutorial examples with illustrative case
studies are provided to demonstrate its functions of dynamic state estimation,
energy flow analysis, security assessment and control, and optimal energy flow.
From the application perspective, real-world engineering demonstrations that
apply IEMSs in managing building-scale, park-scale, and city-scale IESs are
reported. The economic and environmental benefits obtained in these
demonstration projects indicate that the IEMS has broad application prospects
for a low/zero-carbon future energy system.
