Electric Power Generation, Transmission, and Distribution

of the arrow. For instance, the arrow betweenPower FlowandDG Controlindicates thatPower Flowis
used by theDG Controltask. That is,DG Controlcan runPower Flowand obtain power flow results.
Similarly, it can be seen that circuit measurements are made available for use in the load scaling.
All the functions shown in Fig. 24.4 share the same circuit model and circuit data. Exchange of results
among these functions takes place through the common circuit model. The circuit model and data
include the following:

.Topology information of the circuit

.Type, status, rating, configuration, impedance, and=or admittance of the components present in

the circuit

.Location and class of loads connected throughout the circuit

.Historical load measurements

.Load research data for the various classes of loads

Typically, measurements are taken at a very limited number of locations such as at the start of the
circuit and DG sites. Therefore, the main task is to use the circuit model and the available measurements
to estimate the flows in the circuit. That is, the majority of flows are determined by calculations instead
of measurements obtained via data acquisition systems.
The most common scenario concerning control is as follows. Real-time current and voltage meas-
urements taken at the start of the circuit are fed into the circuit model. Real-time kW and kVar
measurements taken at the DGs are also fed into the model.Power Flowthen calculates voltages and
currents throughout the circuit. Since the load data (location, class, historical measurements, and load
research data such as load curves, coincidence, and diversity factors) are already available,Power Flow
usesLoad Scalingfor matching the calculated flows to the measurements.Load Scalingadjusts the circuit
loads until the calculated flows match the measured flows. This is thus an estimation process for
the loads that result in the measured flows.
In case real-time circuit measurements are not available, historical measurements and weather data
are used to estimate loading. From this information, the flows at the start of circuit can be estimated.
Then the estimated flows are used as if they were measurements at the start of the circuit, andLoad
Scalingagain adjusts load sizes so that the estimated and measured flows match.

DG control

Generator constraints

Must-run DG Maximum

DG power

from circuit

kW and kVar

set points for

DGs

Desired DG

from circuit

Load scaling Power flow

Circuit

measurements

Historical

measurements

Weather forecast

FIGURE 24.4 Level-2 DG control functions.