IEEE Power & Energy Magazine - March/April 2015 - 66

interaction between the PV inverter's control systems implementing the advanced functions and other automatic voltage
regulation equipment on the circuits-specifically, the automatically controlled switched capacitors on the three SCE
study circuits.
Figure 2 shows the results from a PV impact mitigation
analysis that investigated the use of the constant power factor operation PV inverter functionality for three different
constant power factor settings and for three salient operating
points, as described above. The figure shows the expected
voltage change, on a 120-V base, at the point of interconnection, for the sudden loss or return of generation for the
5-MW PV system interconnected with the Porterville, California, study circuit. Operating power factor set points are
shown for unity power factor operation up to -0.95 power
factor (absorbing reactive power). These voltage changes
are related to other voltage variation metrics, including the
voltage change that occurs when a nearby capacitor bank
operates. This capacitor normally operates at least twice per
day, resulting in one "on" and one "off" switching event.
From these model-based results, it is clear that operating
the PV systems at an off-unity power factor greatly reduces
the potential voltage-related impacts at the point of interconnection and on the voltage profile of the circuit in general. In addition, the power factor set point that effectively
reduces the maximum voltage change at the point of interconnection to less than 1 V is not unrealistically high and
is certainly implementable in most existing and any future
interconnected PV systems without requiring costly PV
inverter oversizing to accommodate the additional reactive
power processing.
Similar analysis for the other two SCE study circuits
resulted in similar outcomes. In fact, all three circuits analyzed showed that operating the PV system at a constant
power factor of -0.95 (absorbing reactive power) greatly
reduced the voltage variations and the possibility of increasing the operations of the automatic switched capacitors.

(a)

Quantifying the Impact
of High-Penetration PVs
A critical component of this research project has been the
ability to measure and observe the operation of the three SCE
study circuits. To achieve this, a considerable amount of data
acquisition equipment was installed on the circuits, and a
direct supervisory control and data acquisition (SCADA)
link between SCE and the research team was implemented.
An eDNA DataBridge was used to communicate real-time
SCADA values of voltage, current, and real and reactive
power for both the interconnected circuits' substations and
the interconnected PV systems.
Figure 3 presents the two types of data acquisition equipment that were installed on the SCE study circuits to complement the SCE-provided SCADA link. Figure 3(a) shows
a three-phase version of the distribution monitoring unit
(DMU) developed at the National Renewable Energy Laboratory (NREL) specifically for distribution field measurement studies. The DMU is based on phasor measurement
unit (PMU) standards in terms of the implemented measurement algorithms, output data structure, and time synchronization, but it interfaces to the electric power system on the
secondary side of a distribution transformer. The units used
for this study were capable of interfacing at a service voltage
of 480 V/277 V. These DMUs use a cellular communications
backhaul network, and data are stored in a traditional phasor data concentrator at NREL. The units provide 1-s measurements of the three phase voltages and the distribution
transformers' secondary load currents, as well as traditional
PMU measurements like voltage and current phase angles
referenced to a GPS-disciplined clock.
Figure 3(b) and (c) shows a modified commercial solution
that was used to measure distribution line currents using hotstick installable phase current monitors. GridSense modified
its existing LineTracker 40 product, used for low-speed load
logging and fault and outage detection, into a high-speed line
current logger. Three LineTracker 40 units were used at each

(b)

(c)

figure 3. The two types of data acquisition systems deployed on the study circuits to quantify the impact of highpenetration PV integration: (a) a DMU developed by NREL and (b) and (c) a modified version of a commercial product
(LineTracker LT40) by GridSense using overhead line-attached current sensors and a local data concentrator with cellbased data telemetry.
66

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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2015

IEEE Power & Energy Magazine - March/April 2015 - Cover1
IEEE Power & Energy Magazine - March/April 2015 - Cover2
IEEE Power & Energy Magazine - March/April 2015 - 1
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IEEE Power & Energy Magazine - March/April 2015 - Cover3
IEEE Power & Energy Magazine - March/April 2015 - Cover4
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