IEEE Power & Energy Magazine - March/April 2015 - 55

PV

η (PV, Grid)
η-MPP-Tracking

PV

Loads

Battery

)

rid

IEC 62509

G
ry,
atte

B

η(

η(

PV

s,
L

η (Battery, Loads)
η-Load Adjustment

oa

ds

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η (PVs, Battery)

η (PVs, Battery)

η-MPP-Tracking

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Grid

η (PV, Grid)
DIN EN 50530, IEC 61683
)
rid
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r
9
tte
50
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η(
EC
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DIN
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IEC N 50 oads
616 530, )
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η (Battery, Loads)
IEC 62509

Grid

Loads

η (Battery)
(a)

(b)

figure 6. (a) Different energy conversion paths in PV battery systems require tracking of dynamic, time-dependent system
behavior. (b) Applicable norms for the individual conversion paths serve as guidelines for the new benchmarking concept.

march/april 2015

Reverse Power Flows

Load Flow (MVa)

single-branch feeders longer than 1 km.) Cost-benefit analy- controller designs rather than the nature of the control itself.
ses on these so-called smart grid technologies have identi- Park controllers of utility-sized PV systems are good examples. Unusually long communication dead times within a
fied a significant cost savings potential for DSOs.
Figure 8 shows the outcome of a cost-benefit analysis for park controller in combination with fast-acting PV inverters
two actual LV grids in Germany. In addition to various forms can lead to unstable reactive power outputs that are solely
of local reactive power provision and active power control based on the control system's architecture. This problem may
through state-of-the-art PV inverters, MV/LV OLTCs are seem arbitrary but can become a serious issue when park conalso monetarily benchmarked. The figure depicts the grid trollers from third parties that do not technically match up
reinforcement costs as well as the network and PV feed- with the internal controller settings of the installed inverters
in losses, expressed as NPVs, that arise in when a defined are used. Against this background, it is highly likely that Geramount of PV capacity is hosted and assuming the application man grid codes will need to incorporate new requirements
of the smart grid technologies mentioned above. Comparing specifying the relevant controller settings (permissible dead
this approach with classical grid reinforcement reveals that times, filter time constants, and so on) in the years to come.
Active power curtailment of PV systems is presently just
potential cost savings of more than 50% are associated with
the application of these smart grid technologies. The results allowed to guarantee the power system security. It is not yet
facilitated from the regulatory design to use active power
coincide with the outcomes of other studies in this field.
From a technical perspective,
volt/var control-which in Germany
Measured at 110/20-kV Substation, Courtesy of Bayernwek AG
25
is commonly known as Q(U) or
Q(V) control-through PV invert20
ers and other RES is currently
15
considered controversial by GerWinter Peak Load
man DSOs, inverter manufac10
turers, and research institutions.
5
While some DSOs appreciate the
efficiency of volt/var control (reac0
tive power is provided only if it is
-5
needed for voltage support), others
Sum
mer
worry about potential instabilities
-10
Pea
k Lo
ad
resulting from the voltage depen-15
dency of many autonomously
controlled entities. Although the
-20
stability question has not been
-25
conclusively answered, there are
01/01/2009
01/01/2010
01/01/2011
01/01/2012
01/01/2013
strong indicators that instabilities associated with volt/var con- figure 7. Development of active power flows 2009-2013, measured at a
trol may be caused by inadequate 110-kV/20-kV substation in the Bayernwerk AG service area.
ieee power & energy magazine

55



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
IEEE Power & Energy Magazine - March/April 2015 - 2
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IEEE Power & Energy Magazine - March/April 2015 - Cover3
IEEE Power & Energy Magazine - March/April 2015 - Cover4
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