GE DMC490 Software Configuration Manual page 12

DMC490 Microgrid Controller Software Configuration Guide
Figure 7 Droop control operating characteristic
In grid-connected microgrids, the grid compensates for any imbalance between load and generation in the
microgrid, behaving like an isochronous machine for the microgrid. However, for islanded microgrids, there is a
need for an isochronous machine to maintain load-generation balance, and stabilize the frequency around the
nominal value in response to instantaneous load and renewable generation variations above or below the
forecasted values. Such an isochronous machine provides reserve margins in both positive and negative
directions to address the deficit or surplus of power, respectively. These margins are defined as a percent of the
total load in the microgrid.
Isochronous/non-isochronous operation of a generator impacts the behavior of the MGC in the process of
optimally dispatching the generation/storage devices in the microgrid. Thus, generating power of a
dispatchable generator (genset) operating in non-isochronous mode can pick any value between its lower and
upper bounds; however, for an isochronous dispatchable genset, lower and upper bounds of generating power
need to be changed in the optimization problem solved by the MGC so that the reserve margins are respected.
These concepts are demonstrated in Figure 8 and Figure 9, where the highlighted regions specify the intervals
that the generating power (P
dispatchable generating power.
Figure 8 Demonstration of non-isochronous operation of a dispatchable generator
Figure 9 Demonstration of the isochronous operation of a dispatchable generator
A diesel or a CHP unit can usually operate in isochronous mode due to the non-variable nature of their fuel
source, while highly-intermittent renewable power sources such as wind or solar cannot fulfill the requirements
of an isochronous machine. However, the MGC supports the isochronous operation of renewable power
generation units that are relatively less intermittent, such as run-of-the-river hydro units with reservoirs. In
order to support such a feature, a parameter entitled Renewable Capability is defined in the setup program.
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) is allowed to change. PD
D
and PD represent the lower and upper bounds of
min max