IEEE Power & Energy Magazine - July/August 2021 - 56

1
Voltage Magnitudes
at Head of Feeder
Power Flow-Based
Algorithm
2
Net Demand
of Passive Customers
3
4
Operating Envelopes
for Active Customers
1
2
3
This creates the necessary reference point to perform three-phase power flow analyses of the feeder;
i.e., the head of the LV feeder is the slack bus.
Net active and reactive power demand at the connection point of passive customers. Their behavior will affect
the available LV feeder capacity that can be used by active customers.
This algorithm combines the three-phase power flow analysis of the LV feeder and a heuristic process to determine
the maximum feasible power exports of active customers following a specific objective (e.g., maximizing total exports,
maximizing equal individual exports, and so on).
4
The final output is the operating envelopes for all active customers, i.e., the maximum feasible power exports that
ensure network integrity. These are the limits active customers (or their aggregators) must comply with at
the corresponding time interval.
figure 3. The basic process to calculate operating envelopes for a given time interval.
For instance, the more frequently operating envelopes are
calculated, the more accurate the forecasted values and,
therefore, the more accurate the operating envelopes are
expected to be. On the other hand, more frequent calculation
of operating envelopes will require more frequent collection
of the input data, which may not be feasible (or cost-effective)
for the existing supervisory control and data acquisition
(SCADA) and advanced metering infrastructure of the distribution
companies.
Due to the radial and nonlinear nature of distribution
networks, the exports of an active customer located at the
end of a feeder will typically have a larger impact on voltages
than those closer to the head of the feeder. This means
that, depending on the objectives or principles adopted in the
power flow-based algorithm (e.g., finding the largest power
exports), the operating envelopes can be significantly different
for certain active customers. This affects their potential
Head of
Feeder
ability to participate in markets (and receive revenue), raising
fairness and equity concerns.
There is no generic answer to " what is the best objective
function " as it depends on what matters to the stakeholders.
It is extremely important to understand the implications
of different objective functions on active customers and to
make an informed decision on the choice of function.
figure 4. A simplified one-line diagram of the investigated
LV feeder.
56
ieee power & energy magazine
Unlocking Flexibility
A case study is presented in this section to demonstrate how
operating envelopes can ensure network integrity and unlock
additional flexibility for aggregators. A simplified one-line
diagram of the investigated LV feeder is shown in Figure 4;
it is based on a real feeder in Victoria, Australia. For this
analysis, the head of the feeder is treated as the slack bus with
a voltage of 422 V line to line [or 1.055 per unit (pu)]. This
boost in voltage above the nominal is a common practice in
Australia to accommodate voltage drops during peak demand
periods. In this feeder, there are 24 single-phase residential
customers (colored arrows) connected to the three-phase
backbone (black lines). The phase connections are indicated
using colored strokes (red, green, and blue). All customers are
assumed to already have photovoltaic systems installed; for
simplicity, the same system size (3.5 kW peak) is considered.
This case study will consider the effects on customer voltages
if eight of the 24 customers become active customers
july/august 2021

IEEE Power & Energy Magazine - July/August 2021

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